Nutrient Adequacy Of Exclusive Breastfeeding For The Term Infant ...

NUTRIENT ADEQUACY
OF EXCLUSIVE
BREASTFEEDING
FOR THE TERM INFANT
DURING THE FIRST
SIX MONTHS OF LIFE
DEPARTMENT OF NUTRITION FOR HEALTH AND DEVELOPMENT
DEPARTMENT OF CHILD AND ADOLESCENT HEALTH AND DEVELOPMENT
WORLD HEALTH ORGANIZATION

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NUTRIENT ADEQUACY OF
EXCLUSIVE BREASTFEEDING FOR
THE TERM INFANT DURING THE
FIRST SIX MONTHS OF LIFE
NANCY F. BUTTE, PHD
USDA/ARS Children’s Nutrition Research Center, Department of Pediatrics,
Baylor College of Medicine, Houston, TX, USA
MARDIA G. LOPEZ-ALARCON, MD, PHD
Nutrition Investigation Unit, Pediatric Hospital, CMN, Mexico City, Mexico
CUTBERTO GARZA, MD, PHD
Division of Nutritional Sciences, Cornell University, Ithaca, NY, USA
GENEVA
WORLD HEALTH ORGANIZATION
2002

WHO Library Cataloguing-in-Publication Data
Butte, Nancy F.
Nutrient adequacy of exclusive breastfeeding for the term infant during the first six months of life / Nancy F. Butte, Mardia
G. Lopez-Alarcon, Cutberto Garza.
1.Breastfeeding 2.Milk, Human – chemistry 3.Nutritive value 4.Nutritional requirements 5.Infant I.Lopez-Alarcon,
Mardia G. II.Garza, Cutberto III.Expert Consultation on the Optimal Duration of Exclusive Breastfeeding (2001 : Geneva,
Switzerland) IV.Title.
ISBN 92 4 156211 0
(NLM Classification: WS 125)
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Designed by minimum graphics
Printed in France

R E F E R E N C E S
Contents
Abbreviations & acronyms
v
Foreword
vii
Executive summary
1
1. Conceptual framework
3
1.1 Introduction
3
1.2 Using ad libitum intakes to assess adequate nutrient levels
3
1.3 Factorial approaches
4
1.4 Balance methods
5
1.5 Other issues
6
1.5.1 Morbidity patterns
6
1.5.2 Non-continuous growth
6
1.5.3 Estimating the proportion of a group at risk for specific nutrient deficiencies
6
1.5.4 Summary
7
2. Human-milk intake during exclusive breastfeeding in the first year of life
8
2.1 Human-milk intakes
8
2.2 Nutrient intakes of exclusively breastfed infants
8
2.3 Duration of exclusive breastfeeding
8
2.4 Summary
14
3. Energy and specific nutrients
15
3.1 Energy
15
3.1.1 Energy content of human milk
15
3.1.2 Estimates of energy requirements
15
3.1.3 Summary
15
3.2 Proteins
16
3.2.1 Dietary proteins
16
3.2.2 Protein composition of human milk
16
3.2.3 Total nitrogen content of human milk
17
3.2.4 Approaches used to estimate protein requirements
17
3.2.5 Protein intake and growth
20
3.2.6 Plasma amino acids
21
3.2.7 Immune function
21
3.2.8 Infant behaviour
22
3.2.9 Summary
22
iii

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
3.3 Vitamin A
22
3.3.1 Introduction
22
3.3.2 Vitamin A in human milk
22
3.3.3 Estimates of vitamin A requirements
23
3.3.4 Plasma retinol
23
3.3.5 Functional end-points
24
3.3.6 Summary
26
3.4 Vitamin D
26
3.4.1 Introduction
26
3.4.2 Factors influencing the vitamin D content of human milk
26
3.4.3 Estimates of vitamin D requirements
27
3.4.4 Vitamin D status and rickets
29
3.4.5 Vitamin D and growth in young infants
29
3.4.6 Vitamin D and growth in older infants
30
3.4.7 Summary
30
3.5 Vitamin B6
30
3.5.1 Introduction
30
3.5.2 Vitamin B6 content in human milk
30
3.5.3 Approaches used to estimate vitamin B6 requirements
31
3.5.4 Estimates of requirements
31
3.5.5 Vitamin B6 status of breastfed infants and lactating women
31
3.5.6 Growth of breastfed infants in relation to vitamin B6 status
32
3.5.7 Summary
32
3.6 Calcium
32
3.6.1 Human milk composition
32
3.6.2 Estimates of calcium requirements
32
3.6.3 Summary
33
3.7 Iron
34
3.7.1 Human milk composition
34
3.7.2 Estimates of iron requirements
34
3.7.3 Summary
35
3.8 Zinc
35
3.8.1 Human milk composition
35
3.8.2 Estimates of zinc requirements
35
3.8.3 Summary
37
References
38
iv

R E F E R E N C E S
Abbreviations & acronyms
AI
Adequate intake
BMD
Bone mineral density
BMC
Bone mineral content
CDC
Centers for Disease Control and Prevention (USA)
DPT
Triple vaccine against diphtheria, pertussis and tetanus
DXA
Dual-energy X-ray absorptiometry
EAR
Estimated average requirement
EAST
Erythrocyte aspartate transaminase
EPLP
Erythrocyte pyridoxal phosphate
ESPGAN
European Society of Paediatric Gastroenterology
FAO
Food and Agriculture Organization of the United Nations
IDECG
International Dietary Energy Consultative Group
IU
International units
NCHS
National Center for Health Statistics (USA)
NPN
Non-protein nitrogen
PLP
Pyridoxal phosphate
PMP
Pyridoxamine phosphate
PNP
Pyridoxine phosphate
PTH
Parathyroid hormone
RE
Retinol equivalents
SD
Standard deviation
SDS
Standard deviation score
UNICEF
United Nations Children’s Fund
UNU
United Nations University
WHO
World Health Organization
v

R E F E R E N C E S
Foreword
This review, which was prepared as part of the back-
adequacy is most commonly evaluated in terms of
ground documentation for a WHO expert consultation,1
growth, but other functional outcomes, e.g. immune
evaluates the nutrient adequacy of exclusive breast-
response and neurodevelopment, are also considered to
feeding for term infants during the first 6 months of
the extent that available data permit.
life. Nutrient intakes provided by human milk are
This review is limited to the nutrient needs of infants.
compared with infant nutrient requirements. To avoid
It does not evaluate functional outcomes that depend
circular arguments, biochemical and physiological
on other bioactive factors in human milk, or behaviours
methods, independent of human milk, are used to define
and practices that are inseparable from breastfeeding,
these requirements.
nor does it consider consequences for mothers. In
The review focuses on human-milk nutrients, which
determining the optimal duration of exclusive breast-
may become growth limiting, and on nutrients for which
feeding in specific contexts, it is important that func-
there is a high prevalence of maternal dietary deficiency
tional outcomes, e.g. infant morbidity and mortality,
in some parts of the world; it assesses the adequacy of
also are taken into consideration.
energy, protein, calcium, iron, zinc, and vitamins A,
The authors would like to thank the World Health
B6, and D. This task is confounded by the fact that the
Organization for the opportunity to participate in
physiological needs for vitamins A and D, iron, zinc –
the expert consultation;1 and Nancy Krebs, Kim
and possibly other nutrients – are met by the combined
Michaelson, Sean Lynch, Donald McCormick, Paul
availability of nutrients in human milk and endogenous
Pencharz, Mary Frances Picciano, Ann Prentice, Bonny
nutrient stores.
Specker and Barbara Underwood for reviewing the draft
In evaluating the nutrient adequacy of exclusive breast-
manuscript. They also express special appreciation for
feeding, infant nutrient requirements are assessed in
the financial support provided by the United Nations
terms of relevant functional outcomes. Nutrient
University.
1
Expert consultation on the optimal duration of exclusive
breastfeeding, Geneva, World Health Organization, 28–30 March
2001.
vii

E X E C U T I V E S U M M A R Y
Executive summary
In this review nutrient adequacy of exclusive
The dual dependency on exogenous dietary sources and
breastfeeding is most commonly evaluated in terms of
endogenous stores to meet requirements needs to be
growth. Other functional outcomes, e.g. immune
borne in mind particularly when assessing the adequacy
response and neurodevelopment, are considered when
of iron and zinc in human milk. Human milk, which is a
data are available. The dual dependency on exogenous
poor source of iron and zinc, cannot be altered by
dietary sources and endogenous stores for meeting
maternal supplementation with these two nutrients. It
requirements is also considered in evaluating human
is clear that the estimated iron requirements of infants
milk’s nutrient adequacy. When evaluating the nutrient
cannot be met by human milk alone at any stage of
adequacy of human milk, it is essential to recognize the
infancy. The iron endowment at birth meets the iron
incomplete knowledge of infant nutrient requirements
needs of the breastfed infant in the first half of infancy,
in terms of relevant functional outcomes. Particularly
i.e. 0 to 6 months. If an exogenous source of iron is not
evident is the inadequacy of crucial data for evaluating
provided, exclusively breastfed infants are at risk of
the nutrient adequacy of exclusive breastfeeding for the
becoming iron deficient during the second half of
first 4 to 6 months.
infancy. Net zinc absorption from human milk falls short
of zinc needs, which appear to be subsidized by prenatal
Mean intakes of human milk provide sufficient energy
stores.
and protein to meet mean requirements during the first
6 months of infancy. Since infant growth potential
In the absence of studies specifically designed to evaluate
drives milk production, the distribution of intakes likely
the time at which prenatal stores become depleted,
matches the distribution of energy and protein
circumstantial evidence has to be used. Available
requirements.
evidence suggests that the older the exclusively breastfed
infant the greater the risk of specific nutrient
The adequacy of vitamin A and vitamin B6 in human
deficiencies.
milk is highly dependent upon maternal diet and
nutritional status. In well-nourished populations the
The inability to estimate the proportion of exclusively
amounts of vitamins A and B6 in human milk are
breastfed infants at risk of specific deficiencies is a major
adequate to meet the requirements for infants during
drawback in terms of developing appropriate public
the first 6 months of life. In populations deficient in
health policies. Conventional methodologies require
vitamins A and B6, the amount of these vitamins in
that a nutrient’s average dietary requirement and its
human milk will be sub-optimal and corrective measures
distribution are known along with the mean and
are called for, either through maternal and/or infant
distribution of intakes and endogenous stores.
supplementation, or complementary feeding for infants.
Moreover, exclusive breastfeeding at 6 months is not a
The vitamin D content of human milk is insufficient to
common practice in developed countries, and it is rarer
meet infant requirements. Infants depend on sunlight
still in developing countries. There is a serious lack of
exposure or exogenous intakes of vitamin D; if these
measurement, which impedes evaluation, of the human-
are inadequate, the risk of vitamin D deficiency rises
milk intakes of 6-month-old exclusively breastfed
with age as stores become depleted in the exclusively
infants from developing countries. The marked attrition
breastfed infant.
rates in exclusive breastfeeding through 6 months
postpartum, even among women who are both well
The calcium content of human milk is fairly constant
nourished and highly motivated, is a major gap in our
throughout lactation and is not influenced by maternal
understanding of the biological, cultural and social
diet. Based on the estimated calcium intakes of
determinants of the duration of exclusive breastfeeding.
exclusively breastfed infants and an estimated
A limitation to promoting exclusive breastfeeding for
absorption efficiency of > 70%, human milk meets the
the first 6 months of life is our lack of understanding of
calcium requirements of infants during the first
the reasons for the attrition rates. Improved
6 months of life.
understanding of the biological, socioeconomic and
1

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
cultural factors influencing the timing of supplemen-
for mothers been considered. It is important that
tation of the breastfed infant’s diet is an important part
functional outcomes, e.g. infant morbidity and mortality,
of advocating a globally uniform infant-feeding policy
be taken carefully into account in determining the
that accurately weighs both this policy’s benefits and
optimal duration of exclusive breastfeeding in specific
possible negative outcomes.
environments.
It is important to recognize that this review is limited
This review was prepared parallel to, but separate from,
to the nutrient needs of infants. No attempt has been
a systematic review of the scientific literature on the
made to evaluate functional outcomes that depend on
optimal duration of exclusive breastfeeding.1 These
other bioactive factors in human milk, or behaviours
assessments served as the basis for discussion during an
and practices that are inseparable from breastfeeding.
expert consultation (Geneva, 28–30 March 2001),
Neither have the consequences, positive or negative,
whose report is found elsewhere.2
1
Kramer MS, Kakuma R. The optimal duration of exclusive
breastfeeding: a systematic review. Geneva, World Health
Organization, document WHO/NHD/01.08–WHO/FCH/CAH/
01.23, 2001.
2
The optimal duration of exclusive breastfeeding: report of an expert
consultation. Geneva, World Health Organization, document
WHO/NHD/01.09–WHO/FCH/CAH/01.24, 2001.
2

1 . C O N C E P T U A L F R A M E W O R K
1. Conceptual framework
1.1 Introduction
A and D, and zinc). It is becoming increasingly clear
that this is likely the case for iron, zinc and possibly
Dietary surveys of presumably healthy populations,
calcium. Calcium is included because the physiological
factorial approaches (summing needs imposed by growth
significance of the transient lower bone mineral content
and maintenance requirements), and balance
observed in breastfed infants, compared to their formula-
techniques (measuring “inputs and outputs”) are the
fed counterparts, is not understood. Assessing nutrient
methods used most often to estimate nutrient
needs without acknowledging this dual dependency
requirements. None are particularly satisfactory because
likely leads to faulty conclusions.
they seldom adequately address growing concerns that
nutrient intakes support long-term health and optimal
To make matters yet more complicated, it is clear that
functional capacities rather than just avoid acute
there is a range between clear deficiency and “optimal”
deficiency states. These concerns are most evident when
adequacy within which humans adapt. The closer one
considering the nutrient needs of infants because of the
is to deficiency within that range, the more vulnerable
paucity of data for estimating most nutrient
one is to common stresses (e.g. infections) and the less
requirements and the limited number of functionally
one is able to meet increased physiological demands (e.g.
relevant outcome measures for this age group. As these
growth spurts). Perhaps the best examples of the
limitations apply to nearly all the sections that follow,
conceptual difficulties that arise due to the capacity of
they will not be repeated.
humans to “adapt” to a range of intakes are debates that
swirl around the “small is beautiful” proposition and the
Growth is the most commonly used functional outcome
“adaptation to lower energy intakes” viewpoint. The
measure of nutrient adequacy. This outcome is
former has been discredited fairly conclusively while
particularly useful for screening purposes because the
the latter has been abandoned in recent estimates of
normal progression of growth is dependent on many
energy needs; this is in recognition of the fact that
needs being met and many physiological processes
humans can adapt to a range of energy intakes, but at a
proceeding normally. However, this strength also betrays
cost whenever there are sustained deviations from
this outcome’s principal weakness since abnormal
requirement levels (2, 3). Thus, energy requirements
growth is highly non-specific. The single or multiple
are estimated on the basis of multiples of basal metabolic
etiologies of abnormal growth are usually difficult to
rate to ensure that needs are met for both maintenance
ascertain confidently. This is most apparent in the
and socially acceptable and necessary levels of physical
differential diagnosis of failure to thrive found in most
activity (3).
standard paediatric texts (1). Yet, this outcome is key
to present approaches for interpreting dietary surveys,
calculating factorial estimates and evaluating outcomes
of balance studies. Specific issues, which relate to
1.2 Using ad libitum intakes to assess
dependence on growth for estimating nutrient needs
adequate nutrient levels
by each of the above-listed methods, are considered in
The paucity of available functional measures of optimal
most of the sections that follow.
intakes compared to functional measures of deficiency
Another problem that is almost unique to infancy
leads most investigators interested in assessing infant
(possible exceptions may be found in specific processes
nutrient requirements to base their estimates on data
during pregnancy and lactation) is that the normal
concerning nutrient intakes by presumably healthy,
progression of growth and development during this life
exclusively breastfed infants, i.e. those with no overt
stage likely relies on both exogenous sources and
evidence of deficiency. This exercise generally relies on
endogenous stores of nutrients. For exclusively breastfed
estimates of intake volumes and human milk nutrient
infants, these are met by human milk and endogenous
composition. For some studies, estimates of both have
nutrient stores transferred to the infant from the mother
been obtained in the same infant-mother dyad. In most
during gestation (see sections below on iron, vitamins
cases, either milk volume or milk composition is
3

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
assumed. Data on day-to-day variability for either
All intake estimates are derived from nutrient
measure are available for only a few studies. The most
concentrations and human-milk volumes obtained in
notable exceptions to these generalities are require-
studies of self-selected or opportunistic populations. In
ment estimates for energy (4), protein (5) and iron (6).
no case are randomly representative data available for
Factorial approaches are used most commonly to
these types of assessments. When data are available,
estimate average requirements for energy and these two
variability of milk volume and composition are
nutrients.
estimated by pooled weighted variances of specific
studies cited for each nutrient. Unless otherwise stated
Generally speaking, estimates of nutrient requirements
only studies of “exclusively” or “predominantly”
for the first year of life are based on measured intakes of
breastfed infants were used to make these estimates.
human milk during the first 6 months. Estimated needs
during the second 6 months are sometimes determined
To the extent possible no cross-sectional data of milk
by extrapolating from these intake measures. The
volumes and milk composition have been used in
reasons for selecting the first 6 months appear arbitrary.
subsequent sections in order to minimize self-selection
One can offer physiological milestones as a reason for
biases that such data present (11). However, it should
selecting this age, e.g. changes in growth velocities,
be noted that most longitudinally designed studies have
stability in nutrient concentrations in human milk,
significant attrition rates as lactation progresses. Thus,
disappearance of the extrusion reflex, teething, and
these data also present special problems that are difficult
enhanced chewing capabilities. However, the variability
to overcome.
in the ages at which these milestones are reached is far
greater than the specificity that the cut-off suggests.
1.3 Factorial approaches
As noted above, growth may be used to justify selecting
the first 6 months as a basis for estimating nutrient
Factorial approaches are generally based on estimates
requirements, although its use this way has severe
of maintenance needs, nutrient accretion that
limitations. Waterlow & Thomson (7), for example,
accompanies growth, measures of digestibility and/or
concluded that exclusive breastfeeding sustained normal
absorption (bioavailability), and utilization efficiency.
growth for only approximately 3 months. WHO and
The sum of maintenance needs and accretion could be
others have questioned the present international
used to estimate requirement levels if dietary nutrients
reference used to reach this and other conclusions
were absorbed and utilized with 100% efficiency. Since
related to the maintenance of adequate growth (8). At
this does not occur, however, the sum is corrected to
present, there is no universally accepted reference or
account for absorption rates and utilization efficiency.
standard that is used for assessing the normality of either
Generally speaking, with the exception of protein, only
attained growth or growth velocity in infants. In the
maintenance, bioavailability and accretion rates will be
absence of such a reference or standard, rationales used
of concern in the application of factorial approaches
in this review that rely on growth are based on WHO
that target nutrient needs of exclusively human-milk
data (8) for attained growth and growth velocity.
fed infants. Thus, again with the exception of protein,
in the sections that follow the efficiency of utilization
The composition of human milk changes dramatically
of absorbed nutrients will be assumed to be 100%. The
in the postpartum period as secretions evolve from
utilization of absorbed nutrients is determined by the
colostrum to mature milk. The stages of lactation
nutrient’s biological value, which relates to the
correspond roughly to the following times postpartum:
efficiency with which a target nutrient (e.g. protein) is
colostrum (0–5 days), transitional milk (6–14 days), and
assimilated or converted to some functionally active
mature milk (15–30 days). Changes in human-milk
form (e.g. efficiency of use of β-carotene compared to
composition are summarized in Table 1. The first 3 to 4
retinol).
months of lactation appear to be the period of most
rapid change in the concentrations of most nutrients.
Maintenance needs reflect endogenous losses related
After that period nutrient concentrations appear to be
to cellular turnover (e.g. skin desquamation and
fairly stable as long as mammary gland involution has
intestinal epithelial shedding) and unavoidable meta-
not begun (9, 10). However, few studies assess the
bolic inefficiency (e.g. endogenous urinary and biliary
dietary and physiological factors that determine either
losses) of endogenous nutrient sources. Maintenance
the rate of change in nutrient concentrations or inter-
needs for young infants are known with greatest
individual variability. Intake data appearing in
certainty where energy is concerned. Basal and resting
subsequent sections are presented in monthly intervals.
metabolic rates generally are accepted as the best
4

1 . C O N C E P T U A L F R A M E W O R K
Table 1. Human milk composition
Age
Energy
Protein
Vitamin A
Vitamin D
Vitamin B6
Calcium
Iron
Zinc
(months)
(kcalth/g)a
(g/l)a
(µmol/l)b
(ng/l)c
(mg/l)d
(mg/l)a
(mg/l)a
(mg/l)a
1
0.67
11
1.7
645
0.13
266
0.5
2.1
2
0.67
9
1.7
645
0.13
259
0.4
2
3
0.67
9
1.7
645
0.13
253
0.4
1.5
4
0.67
8
1.7
645
0.13
247
0.35
1.2
5
0.67
8
1.7
645
0.13
241
0.35
1
6
0.67
8
1.7
645
0.13
234
0.3
1
7
0.67
8
1.7
645
0.13
228
0.3
0.75
8
0.67
8
1.7
645
0.13
222
0.3
0.75
9
0.67
8
1.7
645
0.13
215
0.3
0.75
10
0.67
8
1.7
645
0.13
209
0.3
0.5
11
0.67
8
1.7
645
0.13
203
0.3
0.5
12
0.67
8
1.7
645
0.13
197
0.3
0.5
a Reference 40.
b Reference 6.
c Reference 122.
d Reference 150.
measure of energy maintenance needs. There are no
iron absorption rates are affected by the status of iron
unassailable estimates of protein maintenance needs of
stores. For iron and other minerals, endogenous or
infants, whether or not breastfed, nor, for that matter,
unavoidable losses and the bioavailability of dietary
are there reliable estimates for any other nutrient. In
sources are measurable simultaneously by multiple-tracer
adults, endogenous losses are estimated from data
stable-isotope methods. Because these measurements are
collected under conditions that limit the target
made at nutrient intakes above zero, estimates of
nutrient’s content in the diet to approximately zero.
bioavailability and endogenous losses include the
unavoidable inefficiencies in both absorption and
Accretion rates are related to nutrient accumulations
utilization that are incurred as intakes rise.
that accompany growth. In infancy, these rates are
estimated from measured growth velocities and
estimates of the composition of tissues gained as part of
1.4 Balance methods
growth.
Balance methodologies also have been used to estimate
Bioavailability generally relates to the availability of
nutrient needs and utilization. The general strengths
nutrients for intestinal absorption (e.g. of ferric versus
and weaknesses of balance methods have been reviewed
ferrous iron and the various forms of calcium commonly
extensively and thus will not be repeated (12). For
found in foodstuffs). The determinants of absorption
present purposes it is sufficient to acknowledge two
are too nutrient-specific to be considered in this general
characteristics of balance methods. The first is that their
introduction. Generally, the host’s physiological state
interpretation often relies heavily on estimates derived
and the physical characteristics of nutrients as consumed
by factorial approaches, that is the appropriateness of
are among the principal determinants of absorption.
retained quantities of target nutrients is determined by
In addition to a nutrient’s obligatory losses that occur
comparison with expected retention based on estimates
even when the target nutrient level falls to
derived by factorial methods. Thus, estimates of growth
approximately zero, unavoidable losses are expected to
velocity and tissue composition are key to interpreting
increase as intake levels rise substantially above zero to
balance results. The second characteristic is that balance
meet physiological needs. This inefficiency is considered
results are complicated by the unidirectional biases that
inconsistently in applications of factorial approaches,
are inherent in the method. These biases always favour
especially where the nutrient needs of infants are
overestimation of retention for two reasons. Firstly,
concerned. In the segments that follow, no allowance
intakes are generally overestimated (i.e. even if balance
is made for this highly probable inefficiency other than
experiments are carefully carried out, it is much easier
in consideration of protein needs, and to the extent that
to miss “spills” than it is to “overfeed”) and, secondly,
5

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
underestimating losses is much likelier than over-
1.5.3 Estimating the proportion of a group at risk for
estimating them (i.e. it is easier to under- than to over-
specific nutrient deficiencies
collect urine, faeces and skin losses).
The third issue relates to the challenges of estimating
the proportion of exclusively breastfed infants at risk of
1.5 Other issues
specific nutrient deficiencies using either the
“probability approach” (14) or the simplified estimated
1.5.1 Morbidity patterns
average requirement (EAR) cut-point method described
Three other issues should also be considered, the first
by Beaton (15). The probability approach estimates the
of which is the estimation of common morbidity
proportion of a target group at risk for a specific nutrient
patterns. Although estimates of nutrient requirements
deficiency/inadequacy based on the distributions of the
reflect needs during health, it is increasingly recognized
target group’s average estimated nutrient requirement
that accumulated deficits resulting from infections – due
and the group’s ad libitum intake of the nutrient of
to decreased intakes and increased metabolic needs and
interest. To use this approach, intakes and requirements
losses – must be replenished during convalescence.
should not be correlated and the distributions of
Thus, it is generally important to consider safety margins
requirements and intakes should be known. The EAR
in estimating nutrient needs. In the case of exclusive
cut-point method is a simplified application of the
breastfeeding, the estimates presented below assume that
probability approach; it can be used to estimate the
infants will demand additional milk to redress
proportion of a population at risk when ad libitum
accumulated energy deficits, that the nursing mother is
intakes and requirements are not correlated, inter-
able to respond to these increased demands, and that
individual variation in the EAR is symmetrically
the increased micronutrient and protein intakes
distributed around the mean, and variance of intakes is
accompanying transient increases in total milk intake
substantially greater than the variance of the EAR. The
correct shortfalls accumulated during periods of illness.
dependence of both approaches on a lack of correlation
These assumptions are based on the generally recognized
between intakes and requirements presents some
well-being of successfully breastfed infants, who
difficulties to the extent that the energy intakes,
experience occasional infections and live under
nutrient requirements and ad libitum milk intakes of
favourable conditions. We recognize that no direct data
exclusively breastfed infants are related to each other.
are available to evaluate these assumptions under less
This difficulty arises because milk production is driven
favourable circumstances and that not enough is known
by the infant’s energy demands and by maternal abilities
to estimate the effects of possible constraints on
to meet them. Thus, as energy requirements rise, so
maternal abilities to respond to transient increased
should the intakes of all human-milk constituents.
demands by infants or constraints imposed by
The nature of the expected correlation can be illustrated
inadequate nutrient stores.
by interrelationships between milk composition and
energy and protein requirements imposed by growth.
The protein-to-energy ratio of mature human milk is
1.5.2 Non-continuous growth
approximately 0.013 g protein/kcalth (16).1 The energy
The second issue is the possibility of non-continuous
cost of growth is approximately 19 kcalth/kg, 12 kcalth/
growth evaluated by Lampl, Veldhuis & Johnson (13).
kg, 9 kcalth/kg and 5 kcalth/kg for the age intervals 3–4
Estimates of nutrient needs based on factorial
months, 4–5 months, 5–6 months and 6–9 months,
approaches assume steady, continuous growth. The
respectively (4). To the degree that increased energy
literature reports observations in support of the
requirements imposed by growth drive increased human-
possibility that growth occurs in spurts during infancy.
milk consumption, the corresponding increase in
Non-continuous growth’s potential demands on
protein intakes will be, respectively, 0.25, 0.15, 0.12
nutrient stores and/or exogenous intakes have not been
and 0.06 g protein/kg for the four above-mentioned age
examined sufficiently, and thus no allowance for “non-
intervals. These values will increase to the extent that
continuous” growth needs is made in these assessments.
non-protein nitrogen (NPN) in human milk is utilizable
(see section 3.2.3). The protein deposited per kg of body
weight appears fairly stable, approximately 0.24 g/kg
from 4 to 9 months of age (4). If we assume a net
absorption rate of 0.85 for human-milk protein and an
efficiency of dietary protein utilization of 0.73, the mean
1
1000 kcal is equivalent to 4.18 MJ.
dietary protein requirement for growth is approximately
th
6

1 . C O N C E P T U A L F R A M E W O R K
0.39 g protein/kg (see section 3.2.3). Thus, although
there is a co-dependency on stores and an exogenous
increased energy needs imposed by growth should
supply to meet physiological needs. Arriving at an EAR
simultaneously drive protein intakes upward, human
for specific nutrients based on the intakes of healthy
milk becomes less likely to meet the infant’s need for
breastfed infants assumes, by definition, “optimal”
protein unless energy requirements for activity increase
nutrient stores. However, this assumption grows
in a manner that corrects the asynchrony described
progressively more precarious as the nutritional status
above. In the absence of such an adjustment, as long as
of pregnant women becomes increasingly questionable.
human milk remains the only source of protein the
growing infant becomes increasingly dependent upon
stable or enhanced efficiencies in protein utilization.
1.5.4 Summary
These types of correlations can be dealt with, in part,
None of the available methods for assessing the nutrient
by suitable statistical techniques, as was demonstrated
needs of infants are entirely satisfactory because they
in the report of the International Dietary Energy
address only short-term outcomes rather than short- and
Consultative Group (IDECG) evaluating protein and
longer-term consequences for health. Of particular
energy requirements (4, 5).
concern is the heavy dependence of most methods on
However, the challenges presented by relationships
growth in the absence of acceptable references/standards
among milk intakes and micronutrient requirements and
of normal attained growth and velocity, and their
intakes are more problematic. Theoretically, the same
normal variability. A similar observation can be made
type of relationship exists among energy and
regarding the paucity of information on the causes of
micronutrient intakes and requirements as described
the high attrition occurring in nearly all longitudinal
above for protein but with an added complication. As
studies of exclusive breastfeeding in the period of
will be evident in the sections that follow, it is clear
interest, i.e. beyond the first 4 months of life. Similarly,
that physiological needs for vitamin A, vitamin D, iron,
poor understanding of the determinants of inter-
zinc and possibly other nutrients are met by the
individual variability in the nutrient content of human
combined availability of nutrients from human milk and
milk creates significant problems in assessing key
nutrient stores transferred from mother to infant during
questions related to the assessment of present methods
late gestation. Thus, dietary nutrient requirements vary
for estimating nutrient requirements in the first year of
with the adequacy of those stores. As a consequence
life. The infant’s co-dependence on nutrient stores
there is inadequate information to estimate “true”
acquired during gestation and nutrients from human
physiological requirements (i.e. the optimal amounts
milk further complicates estimation of nutrient
of a nutrient that should be derived from human milk
requirements. This is particularly vexing in applying
and from stores accumulated during gestation). We
methods for assessing population rates of inadequacy
therefore have inadequate information to estimate what
that require estimates of average nutrient requirements.
the dietary EAR is for any of the nutrients for which
7

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
2. Human-milk intake during exclusive
breastfeeding in the first year of life
2.1 Human-milk intakes
2.3 Duration of exclusive breastfeeding
Human-milk intakes of exclusively and partially
Although reasons for supplementation are not always
breastfed infants during the first year of life in developed
discernible from the literature, evidence to date clearly
and developing countries are presented in Table 2 and
indicates that few women exclusively breastfeed beyond
Table 3, respectively. Studies conducted in presumably
4 months. Numerous socioeconomic and cultural factors
well-nourished populations from developed countries
influence the decision to supplement human milk,
and in under-privileged populations from developing
including medical advice, maternal work demands,
countries in the 1980s–1990s were compiled. In most
family pressures and commercial advertising. Biological
of these studies, human-milk intake was assessed using
factors including infant size, sex, development, interest/
the 24-hour test-weighing method. However, the 12-
desire, growth rate, appetite, physical activity and
hour test-weighing method (17, 18) and the deuterium
maternal lactational capacity also determine the need
dilution method (19–21) were also used in a few cases.
and timing of complementary feeding. However, neither
If details were not provided in the publication regarding
socioeconomic nor cultural nor biological factors have
the exclusivity of feeding, partial breastfeeding was
received adequate systematic attention.
assumed. The overall mean human-milk intakes were
In a longitudinal study in the USA, human-milk intake
weighted for sample sizes and a pooled standard
of infants was measured from 4 to 9 months through
deviation (SD) was calculated across studies.
the transitional feeding period (26). Complementary
Mean human milk intake of exclusively breastfed
feeding was started at the discretion of the mother in
infants, reared under favourable environmental
consultation with the child’s paediatrician. Forty-two
conditions, increases gradually throughout infancy from
per cent (19/45) of the infants were exclusively breastfed
699 g/day at 1 month, to 854 g/day at 6 months and to
until 5 months of age, 40% (18/45) until 6 months,
910 g/day at 11 months of age. The mean coefficient of
and 18% (8/45) until 7 months.
variation across all ages was 16% in exclusively breastfed
In a Finnish study (25), 198 women intended to
infants compared to 34% in partially breastfed infants.
breastfeed for 10 months. The number of exclusively
Milk intakes among the partially breastfed hovered
breastfed infants was 116 (58%) at 6 months, 71 (36%)
around 675 g/day in the first 6 months of life and 530 g/
at 7.5 months, 36 (18%) at 9 months, and 7 (4%) at 12
day in the second 6 months.
months. The reason given for introducing complemen-
There is a notable decrease in sample size in studies
tary feeding before the age of 4 to 6 months was the
encompassing the transitional period from exclusive
infant’s demand appeared greater than the supply of
breastfeeding to partial breastfeeding (22–27).
human milk. This was decided by the mother in 77 cases
and by the investigators in 7 cases. Complementary
feeding reversed the progressive decline in the standard
2.2 Nutrient intakes of exclusively breastfed
deviation score (SDS) for length from −0.52 to −0.32
infants
(p=0.07) during the 6 to 9-month period. These authors
concluded that, although some infants can thrive on
Nutrient intakes derived from human milk were
exclusive breastfeeding until 9 to 12 months of age, on
calculated (Table 4) based on the mean milk intakes of
a population level prolonged exclusive breastfeeding
exclusively breastfed infants from developed countries
carries a risk of nutritional deficiency even in privileged
(Table 2) and human milk composition from well-
populations.
nourished women (Table 1). The small samples of
exclusively breastfed infants between 7 and 12 months
In a study in the USA of growth and intakes of energy
of age limit the general applicability of these calculations
and zinc in infants fed human milk, despite intentions
for older breastfed infants.
to exclusively breastfeed for 5 months, 23% of mothers
added solids to their infant’s diet at 4.5 months; 55%
8

2 . H U M A N - M I L K I N T A K E D U R I N G E X C L U S I V E B R E A S T F E E D I N G I N T H E F I R S T Y E A R O F L I F E
Table 2. Human-milk intake of infants from developed countries
Age (months)
1
2
3
4
5
6
Reference
Country
Mean SD
N Mean SD N
Mean SD N
Mean SD N
Mean SD N
Mean SD N
Exclusively breastfed infants
Butte et al. (19)
USA
691 141 8
724 117 14
Butte et al. (16)
USA
751 130 37
725 131 40
723 114 37
740 128 41
Chandra (22)
Canada
793
71 33
856
99 31
925 112 28
Dewey & Lönnerdal (23)
USA
673 192 16
756 170 19
782 172 16
810 142 13
805 117 11
896 122 11
Dewey et al. (29)
USA (boys)
856 129 34
Dewey et al. (29)
USA (girls)
775 125 39
Goldberg et al. (212)
UK
802 179 10
792 177 10
Hofvander et al. (213)
Sweden
656
25
773
25
776
25
Janas et al. (214)
USA
701
11
709
11
Krebs et al. (28)
USA
690 110 71
Köhler et al. (215)
Sweden
746 101 26
726 143 21
Lönnerdal et al. (216)
Sweden
724 117 11
752 177 12
756 140 12
Michaelsen et al. (40)
Denmark
754 167 60
827 139 36
Neville et al. (24)
USA
668 117 12
694
98 12
734 114 10
711 100 12
838 134 12
820
79 9
Pao et al. (217)
USA
600 159 11
833
2
682
1
Picciano et al. (218)
USA
606 135 26
601 123 26
626 117 26
Rattigan et al. (219)
Australia
1187 217
5
1238 168 5
Salmenperä et al. (61)
Finland
790 140 12
800 120 31
Stuff et al. (220)
USA
735
65 9
Stuff & Nichols (26)
USA
792 111 19
Stuff & Nichols (26)
USA
792 111 19
Stuff & Nichols (26)
USA
734 150 18
729 165 18
Stuff & Nichols (26)
USA
792 189 8
769 198 8
818 166 8
van Raaij et al. (221)
Netherlands
692 122 16
718 122 16
van Raaij et al. (221)
Netherlands
745 131 40
Whitehead & Paul (27)
UK (boys)
791 116 27
820 187 23
829 168 18
790 113 5
922
1
Whitehead & Paul (27)
UK (girls)
677
87 20
742 119 17
775 138 14
814 113 6
838
88 4
Wood et al. (222)
USA
688 137 17
729 178 20
758 201 21
793 215 19
789 195 19
Mean, weighted for sample size
699
731
751
780
796
854
Pooled SD
134
132
130
138
141
118
N
186
354
376
257
131
93
Number of study groups
11
14
17
13
10
8
9

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
Table 2. Human-milk intake of infants from developed countries (continued)
Age (months)
1
2
3
4
5
6
Reference
Country
Mean SD
N Mean SD N
Mean SD N
Mean SD N
Mean SD N
Mean SD N
Partially breastfed Infants
Dewey et al. (29)
USA (boys)
814 183 27
Dewey et al. (29)
USA (girls)
733 155 33
Köhler et al. (215)
Sweden
722 114 13
689 120 12
Krebs et al. (28)
USA
720 130 16
Michaelsen et al. (40)
Denmark
488 232 16
531 277 26
Pao et al. (217)
USA
485
79
4
467 100 11
395 175 6
Paul et al. (223)
UK
787 157 28
824 176 28
813 168 28
717 192 25
593 207 26
Paul et al. (223)
UK
676
87 20
728 141 19
741 182 20
716 233 17
572 225 19
Prentice et al. (224)
UK
741 142 48
785 168 47
783 176 48
717 207 42
588 206 45
Rattigan et al. (219)
Australia
1128216.9 5
Stuff et al. (220)
USA
640
94 17
Stuff & Nichols (26)
USA
703 156 19
595 181 19
Stuff & Nichols (26)
USA
648 196 18
van Raaij et al. (221)
Netherlands
746 175 16
Whitehead & Paul (27)
UK (boys)
648
1
833 123 5
787 172 10
699 204 20
587 188 25
Whitehead & Paul (27)
UK (girls)
601
2
664 258 6
662 267 11
500 194 15
WHO (225)
Hungary
607 123 84
673 144 86
681 147 85
631 168 85
539 150 85
WHO (225)
Sweden
642 149 28
745 148 28
776
95 28
791 131 28
560 208 28
Mean, weighted for sample size
611
697
730
704
710
612
Pooled SD
129
150
149
184
194
180
N
116
227
241
251
163
380
Number of study groups
3
7
9
8
8
15
Age (months)
7
8
9
10
11
12
Reference
Country
Mean SD
N Mean SD N
Mean SD N
Mean SD N
Mean SD N
Mean SD N
Exclusively breastfed Infants
Chandra (22)
Canada
872 126 27
815
97 24
Neville et al. (24)
USA
848
63
6
818 158 3
Salmenperä et al. (61)
Finland
890 140 16
910 133 10
Whitehead & Paul (27)
UK
854
1
Mean, weighted for sample size
867
815
890
910
Pooled SD
118
103
140
133
N
34
27
16
10
Number of study groups
3
2
1
1
10

2 . H U M A N - M I L K I N T A K E D U R I N G E X C L U S I V E B R E A S T F E E D I N G I N T H E F I R S T Y E A R O F L I F E
Table 2. Human-milk intake of infants from developed countries (continued)
Age (months)
7
8
9
10
11
12
Reference
Country
Mean SD
N Mean SD N
Mean SD N
Mean SD N
Mean SD N
Mean SD N
Partially breastfed Infants
Dewey et al. (43)
USA
875 142
8
834
99 7
774 180 5
691 233 5
516 215 6
759
28 2
Dewey et al. (29)
USA (boys)
687 233 25
499 270 20
Dewey et al. (29)
USA (girls)
605 197 25
402 228 22
Krebs et al. (28)
USA
640 150 71
Michaelsen et al. (40)
Denmark
318 201 18
Pao et al. (217)
USA
554
3
Paul et al. (223)
UK
484 182 21
340 206 18
251 274 12
Paul et al. (223)
UK
506 255 16
367 266 12
443 319 7
Prentice et al. (224)
UK
493 216 38
342 228 31
328 292 19
Rattigan et al. (219)
Australia
884 252 4
880
74 4
Stuff & Nichols (26)
USA
551 142 19
Stuff & Nichols (26)
USA
602 186 18
522 246 18
Stuff & Nichols (26)
USA
677 242
8
645 250 8
565 164 8
van Raaij et al. (221)
Netherlands
573 187 16
Whitehead & Paul (27)
UK (boys)
484 181 21
342 203 18
Whitehead & Paul (27)
UK (girls)
481 246 15
329 242 11
WHO (225)
Sweden
452 301 28
Mean, weighted for sample size
569
417
497
691
516
497
Pooled SD
188
226
249
233
215
238
N
251
123
154
5
6
48
Number of study groups
11
8
11
1
1
4
Table 3. Human-milk intake of infants from developing countries
Age (months)
1
2
3
4
5
6
Reference
Country
Mean SD
N Mean SD N
Mean SD N
Mean SD N
Mean SD N
Mean SD N
Exclusively breastfed infants
Butte et al. (20)
Mexico
885 146 15
Cohen et al. (30)
Honduras
806
50
824
50
823
50
Gonzalez-Cossio et al. (226)
Guatemala
661 135 27
749 143 27
776 153 27
Naing & Co (18)
Myanmar
423
20 29
480
20 29
556
30 29
616
16 24
655
27 17
751
15 6
van Steenbergen et al. (227)
Indonesia
828
41
5
862 184 6
732
90 5
768 109 6
728 101 3
727 224 8
Mean, weighted for sample size
562
634
582
768
778
804
Pooled SD
92
110
42
63
83
76
N
61
62
34
95
97
64
Number of study groups
3
3
2
4
4
3
11

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
Table 3. Human-milk intake of infants from developing countries (continued)
Age (months)
1
2
3
4
5
6
Reference
Country
Mean SD
N Mean SD N
Mean SD N
Mean SD N
Mean SD N
Mean SD N
Partially breastfed Infants
Butte et al. (20)
Mexico
869 150 15
Cohen et al. (30)
Honduras
799
47
688
47
699
47
Cohen et al. (30)
Honduras
787
44
731
44
725
44
Coward et al. (21)
Papua New Guinea
670 190 17
de Kanashiro et al. (17)
Peru
685 245129
690 240126
655 226113
Frigerio et al. (228)
Gambia
738
47 16
Gonzalez-Cossio et al. (226)
Guatemala
655 198 26
726 153 26
721 166 26
720 165 26
Gonzalez-Cossio et al. (226)
Guatemala
719 138 22
789 112 22
804 128 22
776 121 22
Gonzalez-Cossio et al. (226)
Guatemala
887 125 27
727 113 27
769 128 27
771 117 27
Hennart & Vis (229)
Central Africa
517 169
8
605
78 22
525
95 29
Prentice et al. (224)
Gambia
649 113
7
705 183 8
782 168 6
582 169 10
643 149 17
van Steenbergen et al. (228)
Kenya
778 180
7
619 197 13
573 208 9
van Steenbergen et al. (227)
Indonesia
693 138 32
691 117 31
712 118 29
725 131 30
691
97 31
664 109 26
WHO (225)
Guatemala (urban)
524 246 32
561 222 30
653 255 28
WHO (225)
Philippines (urban)
336 191 34
404 242 25
320 200 20
344 244 10
374 117 16
WHO (225)
Guatemala (urban)
519 186 28
548 173 30
586 185 28
WHO (225)
Philippines (urban)
502 176 32
577 154 23
693 117 32
586 167 27
597 214 30
WHO (225)
Guatemala (rural)
543 131 28
686 151 27
588 142 28
WHO (225)
Philippines (rural)
571 187 27
689 216 30
622 221 28
613 201 23
589 136 29
WHO (225)
Zaire (urban)
609 244 135
656 256156
588 202 99
607 185 58
641 198115
WHO (225)
Zaire (rural)
338 159 52
355 132 50
356 173 57
368 147 66
357 170 99
Mean, weighted for sample size
568
636
574
634
714
611
Pooled SD
196
212
182
177
107
166
N
497
590
391
441
223
694
Number of study groups
15
14
12
10
8
16
Age (months)
7
8
9
10
11
12
Reference
Country
Mean SD
N Mean SD N
Mean SD N
Mean SD N
Mean SD N
Mean SD N
Exclusively breastfed infants
van Steenbergen et al. (227)
Indonesia
740
7
2
691 143 6
Mean, weighted for sample size
740
691
Pooled SD
7
143
N
2
6
Number of study groups
1
1
12

2 . H U M A N - M I L K I N T A K E D U R I N G E X C L U S I V E B R E A S T F E E D I N G I N T H E F I R S T Y E A R O F L I F E
Table 3. Human-milk intake of infants from developing countries (continued)
Age (months)
7
8
9
10
11
12
Reference
Country
Mean SD
N Mean SD N
Mean SD N
Mean SD N
Mean SD N
Mean SD N
Partially breastfed Infants
Coward et al. (21)
Papua New Guinea
936 173
8
de Kanashiro et al. (17)
Peru
624 219 110
565 208 100
Hennart & Vis (229)
Central Africa
580
73 39
582
55 43
van Steenbergen et al. (227)
Indonesia
617
80 28
635 149 23
WHO (225)
Philippines (urban)
321 156 16
WHO (225)
Philippines (urban)
558 183 31
548 158 29
WHO (225)
Guatemala (urban)
587 186 28
WHO (225)
Zaire (urban)
613 193 72
593 192 60
WHO (225)
Guatemala (rural)
602 187 28
WHO (225)
Philippines (rural)
534 176 32
502 185 26
WHO (225)
Zaire (rural)
378 153 91
407 174 85
Mean, weighted for sample size
688
635
516
565
511
Pooled SD
106
149
167
208
164
N
36
23
337
100
243
Number of study groups
2
1
8
1
5
Table 4. Nutrient intakes derived from human milka
Human
Human
milk
milk intake,
Energy
Vitamin
Vitamin
Vitamin
Age
intake
corrected for
(kcalth/
Protein
A
D
B6
Calcium
Iron
Zinc
(month)
(g/day)
IWLb (g/day)
day)
(g/day)
(µmol/day) (ng/day)
(mg/day)
(mg/day)
(mg/day) (mg/day)
1
699
734
492
8.1
1.25
473
0.1
195
0.37
1.54
2
731
768
514
6.9
1.3
495
0.1
199
0.31
1.54
3
751
803
538
7.2
1.37
518
0.1
203
0.32
1.20
4
780
819
549
6.6
1.39
528
0.11
202
0.29
0.98
5
796
836
560
6.7
1.42
539
0.11
201
0.29
0.84
6
854
897
601
7.2
1.52
578
0.12
210
0.27
0.90
7
867
910
610
7.3
1.55
587
0.12
208
0.27
0.68
8
815
856
573
6.8
1.45
552
0.11
190
0.26
0.64
9
890
935
626
7.5
1.59
603
0.12
201
0.28
0.70
10
900
945
633
7.6
1.61
610
0.12
198
0.28
0.47
11
910
956
640
7.6
1.62
616
0.12
194
0.29
0.48
a Nutrient intakes calculated based on the mean milk intakes of exclusively breastfed infants from developed countries (Table 2) and human
milk composition from well-nourished women (Table 1).
b IWL = insensible water losses.
13

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
added solids at 6 months and 93% added solids at
12% in controls to 50% and 67% in the experimental
7 months (28).
groups (31). Rates of exclusive breastfeeding were 12%
in controls and 38–50% in experimental groups.
In a Canadian study, the growth performance of 36
Although the programme succeeded in promoting
exclusively breastfed infants was monitored (22). The
exclusive breastfeeding, it did not approach the goal of
number (percent) of children displaying growth faltering
exclusive breastfeeding for 6 months.
– defined as below the NCHS 10th weight-for-age
percentile – increased from 3 (8.3%) at 4 months to 5
Meanwhile, in Dhaka, Bangladesh, counsellors – local
(13.6%) at 5 months, 8 (22.2%) at 6 months, 9 (25%)
mothers who received 10 days’ training – paid 15 home-
at 7 months, and 12 (33.3%) at 8 months. Even in well-
based counselling visits (2 in the last trimester of
nourished women, exclusive breastfeeding did not
pregnancy, 3 early postpartum, and fortnightly until
sustain growth beyond 4 months of age according to
infants were 5months old) in the intervention group
the 1977 growth curves; furthermore, growth faltering
(32). For the primary outcome, the prevalence of
was associated with higher rates of infectious morbidity.
exclusive breastfeeding at 5 months was 202/228 (70%)
for the intervention group and 17/285 (6%) for the
Breastfed boys consistently consumed more human milk
control group. For the secondary outcomes, mothers in
than breastfed girls did (29, 27). Girls tended to be
the intervention group initiated breastfeeding earlier
exclusively breastfed longer than boys were; comp-
than control mothers and were less likely to give
lementary foods were offered to boys at 4.1 months and
prelacteal and postlacteal foods. At day 4, significantly
to girls at 4.9 months (27). In the same study, after 4
more mothers in the intervention group breastfed
months only 20% of the boys and 35% of the girls were
exclusively than controls.
exclusively breastfed. Complementary feeding resulted
in some increase in total energy intake in boys but not
in girls.
2.4 Summary
Since exclusive breastfeeding is rare in developing
Longitudinal studies conducted among well-nourished
countries, the number of observational studies on
women indicate that, during exclusive breastfeeding,
human-milk intakes of exclusively breastfed infants is
human-milk production rates gradually increase from
limited. An intervention study was conducted in
~700 g/day to 850 g/day at 6 months. Because of the
Honduras where one group (n=50) was required to
high attrition rates in these studies, the corresponding
breastfeed exclusively for 6 months (30). Although this
milk-production rates represent only a select group of
is an important study, it may not be totally represen-
women and thus do not reflect the population variability
tative of all mothers and infants in that community.
in milk production and infant nutrient requirements.
Sixty-four women were ineligible to participate because
they did not maintain exclusive breastfeeding through
Exclusive breastfeeding at 6 months is not a common
16 weeks for the following reasons: insufficient milk
practice in developed countries and appears to be rarer
(n=26), personal choice (n=16), maternal health
still in developing countries. Moreover, there is a serious
(n=12), and family pressure not to breastfeed exclusively
lack of documentation and evaluation of human-milk
(n=10). Weight gain (1092 ± 356 g) in the exclusively
intakes of 6-month-old exclusively breastfed infants
breastfed group was similar to the supplemented groups;
from developing countries. A limitation to the uniform
however, the SD (± 409 g) of weight gain of exclusively
recommendation of exclusive breastfeeding for the first
breastfed infants of mothers with low BMI was greater
6 months of life is the lack of understanding of reasons
than the supplemented infants in both groups. It is
for the marked attrition rates in exclusive breastfeeding,
unclear whether all infants were growing satisfactorily.
even among highly motivated women, in the lactation
Based on this limited number of studies, intakes of
period of interest.
exclusively breastfed infants were, on average, similar
The limited relevant evidence suggests that sufficiency
to those of infants between 4 and 6 months of age from
of exclusive breastfeeding is infant-specific (e.g. based
developed countries.
on sex, size and growth potential), in addition to being
More recently, encouraging results have accrued from
linked to maternal lactational capacity and environ-
community-based breastfeeding promotion programmes
mental factors that may affect an infant’s nutritional
in developing countries. For example, an intervention
needs and a mother’s ability to respond to them.
conducted in Mexico to promote exclusive breastfeeding
Nevertheless, recent intervention studies suggest that
succeeded in increasing rates of predominant breast-
these variables are amenable to improvement in the
feeding above controls at 3 months postpartum from
presence of adequate support.
14

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
3. Energy and specific nutrients
3.1 Energy
Total energy requirements of breastfed infants (Table
5) were estimated using weight at the 50th percentile
3.1.1 Energy content of human milk
of the WHO pooled breastfed data set (8). An allowance
Proteins, carbohydrates and lipids are the major
for growth was derived from the weight gains at the
contributors to the energy content of human milk (33).
50th percentile of the WHO pooled breastfed data set
Protein and carbohydrate concentrations change with
(8), the rates of fat and protein accretion, and the energy
duration of lactation, but they are relatively invariable
equivalents of protein and fat deposition taken as 5.65
between women at any given stage of lactation. In
kcalth/g and 9.25 kcalth/g, respectively (37). The TEE
contrast, lipid concentrations vary significantly between
of breastfed infants (36) was predicted at monthly
both individual women and populations, which
intervals using the equation TEE (kcalth/day) = 92.8 *
accounts for the variation observed in the energy
Weight (kg) – 151.7.
content of human milk.
Energy intakes based on the mean milk intakes of
Differences in milk sampling and analytical methods
exclusively breastfed infants appeared to meet mean
also contribute to the variation in milk energy (34, 35).
energy requirements during the first 6 months of life.
Within-day, within-feeding, and between-breast
Since infant size and growth potential drive energy
variations in milk composition; interference with milk
intake, it is reasonable to assume a positive relationship
“let-down”; and individual feeding patterns affect the
between energy intake and energy requirements.
energy content of human milk. In the present context,
Positive correlations between energy intake and infant
two milk-sampling approaches have been used to
weight, and energy intake and weight gain, have been
estimate the energy content of human milk – expression
reported (37–39). The matching of intake to require-
of the entire contents of one or both breasts at a specific
ments for energy is unique in this regard. Thus, it is
time or for a 24-hour period, and collection of small
likely that infant energy needs can be met for 6 months,
aliquots of milk at different intervals during a feed.
and possibly longer, by women wishing to breastfeed
Human milk’s energy content was determined directly
exclusively this long. The major shortcoming appears
from its heat of combustion measured in an adiabatic
to be the marked attrition rates in exclusive breast-
calorimeter, or indirectly from the application of
feeding, even among women who seem to be highly
physiological fuel values to the proximate analysis of
motivated and who have presumably good support
milk protein, lactose and fat.
networks. There is a major gap in our understanding
of the role – and the relative positive or negative
The mean energy content of human milk ranges from
contribution – of biological and social determinants of
0.62 kcalth/g to 0.80 kcalth/g (33). For present purposes,
observed attrition rates.
a value of 0.67 kcalth/g has been assumed.
3.1.3 Summary
3.1.2 Estimates of energy requirements
Energy requirements derived from the sum of total
The energy requirements of infants may be derived from
energy expenditure and energy deposition were used to
total energy expenditure and energy deposition (4).
evaluate the adequacy of human milk to support the
Total energy expenditure was measured by using the
energy needs of exclusively breastfed infants. Energy
doubly labelled water method and energy deposition
intakes based on the mean milk intakes of exclusively
from protein and fat accretion in breastfed and formula-
breastfed infants appear to meet mean energy
fed infants at 3, 6, 9, 12, 18 and 24 months of age (36).
requirements during the first 6 months of life. Since
In this study, the mean coefficient of variation for total
infant growth potential drives milk production, it is
energy expenditure (TEE) and total energy requirements
likely that the distribution of energy intakes matches
were 18% and 17%, respectively, across all ages.
the distribution of energy requirements. Women who
15

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
Table 5. Energy requirements of breastfed Infants
Weight
Total energy
Energy
Energy
Weight
velocity
expenditure
deposition
requirement
(kg)a
(g/day)a
(kcalth/day)b
(kcalth/day)c
(kcalth/day)
Boys
1
4.58
35.2
273
211
485
2
5.50
30.4
359
183
541
3
6.28
23.2
431
139
570
4
6.94
19.1
492
53
546
5
7.48
16.1
542
45
588
6
7.93
12.8
584
36
620
7
8.3
11
619
17
635
8
8.62
10.4
648
16
664
9
8.89
9
673
14
687
10
9.13
7.9
696
21
717
11
9.37
7.7
718
21
739
12
9.62
8.2
741
22
763
Girls
1
4.35
28.3
252
178
430
2
5.14
25.5
325
161
486
3
5.82
21.2
388
134
522
4
6.41
18.4
443
68
511
5
6.92
15.5
490
57
548
6
7.35
12.8
530
47
578
7
7.71
11
564
20
584
8
8.03
9.2
593
17
610
9
8.31
8.4
619
15
635
10
8.55
7.7
642
18
660
11
8.73
6.6
663
15
678
12
9
6.3
684
14
698
a Reference 8.
b Reference 36.
c Reference 37.
wish to breastfeed exclusively can meet their infants’
3.2.2 Protein composition of human milk
energy needs for 6 months.
The protein content of mature human milk is approx-
imately 8–10 g/l (33). The concentration of protein
3.2 Proteins
changes as lactation progresses. By the second week
postpartum, when the transition from colostrum to
3.2.1 Dietary proteins
mature milk is nearly complete, the concentration of
Dietary proteins provide approximately 8% of the
protein is approximately 12.7 g/l (40). This value drops
exclusively breastfed infant’s energy requirements and
to 9 g/l by the second month, and to 8 g/l by the fourth
the essential amino acids necessary for protein synthesis.
month where it appears to remain until well into the
Thus, the quantity and quality of proteins are both
weaning process when milk volumes fall substantially.
important. Because protein may serve as a source of
At this point protein concentrations increase as
energy, failure to meet energy needs decreases the
involution of the mammary gland progresses. The inter-
efficiency of protein utilization for tissue accretion and
individual variation of the protein content of human
other metabolic functions. Protein undernutrition
milk, whose basis is unknown (41), is approximately
produces long-term negative effects on growth and
15%.
neurodevelopment.
Several methods have been used to analyse the protein
content of human milk and each has yielded different
results with implications for the physiology and
16

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
nutrition of the breastfed infant (42). Direct analyses
consensus in the literature as to whether low-protein
include the determination of total nitrogen by the
diets result in reduced milk volumes, and therefore in
Kjeldahl method and total amino-acid analysis. To
reduced protein outputs (47, 46, 48). Longer-term
derive the protein nitrogen content by the Kjeldahl
studies are needed in diverse populations to help resolve
method, the NPN fraction is separated by acid
these gaps in knowledge.
precipitation. Indirect analyses based on the protein
molecule’s characteristics include the Biuret method
(peptide bond), Coomassie-Blue/BioRad, BCA method
3.2.3 Total nitrogen content of human milk
(dye-binding sites) and the Lowry method (tyrosine and
Human milk’s total nitrogen content, which appears to
phenylalanine content). The Biuret method, whose
depend on the stage of lactation and dietary intakes,
results conflict with the BCA method, is not
ranges from 1700 to 3700 mg/l. Eighteen to 30% of the
recommended for use in human milk because of high
total nitrogen in milk is non-protein nitrogen (NPN).
background interference. The Lowry method, although
Approximately 30% of NPN are amino acids (5, 49)
efficient, is subject to technical difficulties (e.g.
and thus should be fully available to the infant. As much
spectrophotometric interference by lipids and cells,
as 50% of NPN may be bound to urea (5, 49) and the
differential reaction of proteins in human milk with the
remaining approximately 20% is found in a wide range
colour reagent, and appropriate protein standard
of compounds such as nitrogen-containing carbo-
representative of complex, changing mixture). The
hydrates, choline, nucleotides and creatinine (50).
protein content of mature human milk is approximately
Changes in the relative composition of non-protein
9 g/l by the Kjeldahl method (33), and approximately
nitrogen, as lactation progresses, are not well described.
12–14 g/l by the Lowry and BCA methods (43, 23, 44).
From the limited information available, NPN appears
The 25% higher values obtained by the Lowry method
to decrease by approximately 30% over the first
have been attributed to using bovine serum albumin
3 months of lactation (51). If this nitrogen fraction
(BSA), which has fewer aromatic amino acids than
behaves similarly to protein, it should remain stable
human milk, as the standard. As a result, some investi-
thereafter until possibly weaning is well under way.
gators have adjusted milk-protein concentrations
determined by the Lowry method (45).
Although it is known that the stage of lactation
3.2.4 Approaches used to estimate protein
influences the content and relative amounts of protein
requirements
in human milk, the physiological mechanisms that
Several approaches have been used to estimate protein
regulate their levels have not been identified nor has
requirements for infants and children. At present the
the role of diet been well defined. Based on field studies,
protein intake of breastfed infants from 0 to 6 months
human milk’s total protein concentration does not
of age is considered the standard for reasons reviewed
appear to differ among populations at distinct levels of
by the 1994 IDECG report on protein and energy
nutritional risk. However, difficulties arise in
requirements (5). However, two other approaches also
interpreting published data because total protein
have been used to assess the protein requirements of
content often has been estimated from measurements
infants – balance methods and factorial estimations.
of total nitrogen. This presents problems because in
The 1985 FAO/WHO/UNU Report on Energy and
well-nourished populations approximately 25% of
Protein Requirements (52) states the rationale for using
nitrogen is not bound to protein. However, in contrast
the protein intakes of exclusively breastfed infants from
to conclusions reached in field studies, when dietary
0 to 6 months of age to estimate requirements: “The
protein was increased from 8 to 20% of energy
protein needs of an infant will be met if its energy needs
consumption in metabolically controlled studies,
are met and the food providing the energy contains
protein N concentrations increased by approximately
protein in quantity and quality equivalent to that of
8%, and 24-hour outputs of protein N increased by
breast milk.” This assumes that decreases in the protein
approximately 21%, in the milk of well-nourished
content of human milk are synchronous with decreases
women (46).
in energy requirements expressed per kg of body weight
Extrapolation from metabolically controlled studies to
from 0 to 6 months of age, and that the apparently high
free-living subjects requires caution. Results from field
efficiency of protein utilization in early infancy is
studies may reflect chronic adaptations; those from
sustained at and beyond 6 months of age. There is no
shorter-term laboratory studies may represent acute
scientific evidence that seriously questions these
responses to dietary change. There also is a lack of
assumptions in relation to utilization efficiency (see
17

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
Table 6. Efficiency of protein utilization: growth and body composition of breastfed infants and infants
consuming infant formula with varying protein concentrations
Reference
N
Age
Type of
Growth
LBM
Efficiency of
(months)
feeding
protein utilization
Butte & Garza (58)
40
0–4
BF
60th percentile
W/L
Heinig et al. (45)
71
3–12
BFa
Similar to FF
Higher in FF
Higher in BF
46
FF
Motil et al. (231)
10
1.5–6
BF
60 pct
Similar to FF
Similar to FF
10
FF
Similar to FF
Salmenperä et al. (61)
202
4–12
BF
FF
Åkeson et al. (62)
27b
6
BF
Similar among
10
FF-13
groups
9
FF-15
8
FF-18
Nielsen et al. (232)
339
10
BF> 7 months
13.7 g/day
BF< 7 months
12.5 g/day
Butte et al. (20)
15
4
BF
Drop growth
15
6
velocity
Dewey et al. (63)
50
5–6
BF
Similar weight
91
Partial BF
and length gain
Abbreviations:
W/L: weight-for-length percentile of the NCHS reference, 1977
LBM: lean body mass
BF: breastfed
FF: formula-fed
a Breastfeeding and solids after 6 months.
b Sample size varies because breastfed infants were changed to formula.
Table 6), but changes in energy and protein
losses when milk intakes are determined by test-
requirements for growth do not appear to be
weighing techniques, although this probably represents
proportionately synchronous. Evolutionary arguments
a trivial source of error); and failures to account for
presented for or against the adequacy of exclusive
either the non-protein component of human milk or
breastfeeding are equally unconvincing because of their
the possible under-utilization of some of the milk’s
basic teleological character. As will be evident below,
protein constituents because of their resistance to
the absence of sounder physiological data makes the
digestion. The following reasons are posited for these
use of human milk intakes during this age interval the
inaccurate estimates.
best available choice.
Discomfort with reliance on intake data collected mostly
The 1996 IDECG report on energy and protein
under “opportunistic” situations has led to comparing
requirements (5) reviewed the flaws in the 1985 FAO/
estimates based on ad libitum intakes with nitrogen
WHO/UNU protein requirement estimates for infants
balance data, and “armchair estimates” based on the
(52). These are the assumption that at 1 month of
factorial approach. Of the two bases for comparisons,
lactation protein concentrations in milk are sustained
balance data are less satisfactory. Many of the difficulties
(indeed, as discussed above, they fall); possible
with balance data arise because often they have been
underestimation of milk-intake volumes (because some
obtained from undernourished infants during repletion,
investigators decided not to measure insensible water
or from premature infants. In either case these infants’
18

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
physiological condition renders difficult extrapolation
utilization for growth in the intake range of interest.
to healthy term infants. Moreover, the complexities
Most studies that have examined the absorption of
imposed by relationships between energy intake and
human-milk nitrogen and specific human milk-protein
efficiencies of protein utilization, and by differences in
components have been preformed among premature
utilization efficiencies due to the varying biological
infants (55, 56). In examining this issue, Donovan et
values and amounts of proteins fed in balance studies,
al. (55) reported apparent absorption rates of 85%,
significantly lessen the value of balance results for the
which confirmed earlier data published by Schanler et
purpose of directly estimating protein requirements for
al. (56). These rates of absorption are remarkably similar
healthy term infants.
to those summarized by Fomon (57) for infants fed
various types of cow’s milk-based formulas. These
Thus, the factorial approach, which requires estimating
estimates all include losses of both dietary and
maintenance needs, protein accreted during growth and
endogenous nitrogen, thus available data likely
efficiency of utilization, appears more attractive than
underestimate “true” dietary absorption rates. If we
balance methods. Maintenance needs are based on
nevertheless accept the value for purposes of estimating
obligatory losses and the progressive loss of efficiency
dietary N requirements, the figure adjusted for
in protein utilization as levels of protein increase.
absorption is 125 mg N/kg per day.
Utilization efficiency is believed to be maximal below
requirement levels and to become progressively less
Taking this “conservative” approach, however, is not
efficient as requirement levels are approached and
as unbalanced as it may first appear. The absorption of
surpassed.
human milk’s immunological components has been a
major concern because of their functional role and
The 1996 IDECG report used results from multiple
putative resistance to digestion. Studies examining this
studies to estimate maintenance needs (5). This
issue also have been performed principally in preterm
estimate was calculated by extrapolating relationships
infants (55, 56). Analyses by Donovan et al. (55) for
between nitrogen intake and retention to a y intercept
specific components suggested a maximum absorption
of 10 mg N/kg per day to account for integumental
rate of 75% for SIgA and 91% for lactoferrin. The
losses, and by adjusting relationships between intake
apparent absorption rates for lactoferrin reported by
and retention to an assumed slope of 0.73. In the report
these investigators agree with the earlier studies
the maintenance requirement was estimated to be 90
published by Schanler et al. (56). However, the SIgA
mg N/kg per day. An alternative approach, which
values in the two studies are quite different. Schanler
requires fewer assumptions and less manipulation of
et al. (56) reported total apparent SIgA absorption rates
experimental data, is the use of basal metabolism to
of 91% compared to the mean of 75% by Donovan et
estimate obligatory losses (53). Although this approach
al. (55). This disparity likely reflects the different
was abandoned in the 1985 report because of
analytical methods used for measuring SIgA.
inconsistent ratios across several ages, it appears
reasonably consistent in the age range of interest, i.e.
The estimated requirement for efficiency of utilization
the range of values in published studies of children 4 to
must also be corrected. Once again, the best data have
15 months of age is 1.2 to 1.5 mg N per “basal” kcal
been published from studies of premature infants. If we
th
(53). For 1- and 4-month-old exclusively breastfed
accept the efficiency of utilization of 0.73 adopted by
infants, minimal observable energy expenditure rates
the IDECG group, the N needs of infants in this age
are approximately 45 kcal
range are approximately 171 mg N/kg per day.
th/kg per day (54). If one uses
1.5 mg N per “basal” kcalth as a conservative estimate,
This estimate compares well with the mean protein N
obligatory losses are 68 mg N/kg per day and extrapo-
intakes reported by Butte et al. (16) for breastfed infants
lations of this value to 6 or 8 months present no
at 1 and 2 months of age. By 3 months of age the sum of
substantial problems since major changes in basal
the mean protein N intake and 30% of the mean NPN
metabolism are not anticipated at these ages. The mean
(assuming that this fraction consists of free amino acids)
protein gain between 4 and 8 months of age for
is 178 mg. By 4 months of age this sum is 161 mg N/kg,
exclusively breastfed infants is 0.24 g protein/kg of body
still reasonably close to the mean estimated
weight/day or 38 mg N/kg per day. The sum of nitrogen
requirement.
needs for maintenance and growth is 106 mg N/kg per
This leaves us with the remainder of the NPN un-
day.
accounted for in terms of its potential utilization. Rates
However, this sum must be corrected for the absorption
of NPN utilization vary greatly from approximately 10%
rate of human-milk proteins and the rate of protein
to almost 50% (5). Given the very incomplete know-
19

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
Table 7. Protein intake of breastfed and formula-fed infants
Type
Protein intake (g/kg per day)
of
Reference
N
feeding
1
2
3
4
6
9
12
Growth
Butte & Garza (58)
40
BF
1.6 ± 0.3
1.1 ± 0.2
1.0 ± 0.2
0.9 ± 0.2
60th percentile
W/L
Heinig et al. (45)
71
BF
1.09 ± 0.2
1.06 ± 0.3
1.67 ± 0.89 2.45 ± 1.1
Similar
46
FF
1.81 ± 0.3
1.76 ± 0.3
2.03 ± 0.4
2.48 ± 0.6
Motil et al. (231)a
10
BF
22 ± 3
14 ± 2
12 ± 3
Similar
10
FF
29 ± 5
25 ± 6
27 ± 10
Åkeson et al. (62)
27b
BF
1.39 ± 0.2
1.67 ± 0.9
2.45 ± 1.1
Similar
10
FF-13
1.87 ± 0.2
2.01 ± 0.3
2.48 ± 0.4
9
FF-15
2.0 ± 0.2
2.18 ± 0.4
2.63 ± 0.5
8
FF-18
2.3 ± 0.2
2.32 ± 0.5
2.73 ± 0.3
Butte et al. (20)
15
BF
1.2 ± 0.3
Drop growth
15
1.1 ± 0.3
velocity
Dewey et al. (63)c
50
BF
0.98 ± 0.2
Similar
91
Partial
1.18 ± 0.2
BF
Abbreviations:
BF: breastfed
FF: Formula-fed
W/L: weight-for-length percentile of the NCHS reference, 1977
a Proteins are in mmol/kg per day.
b Sample size varies because breastfed infants were changed to formula.
c Breastfeeding and solids after 6 months.
ledge of factors that account for this five-fold range in
Z-scores of these infants’ weights and lengths were
utilization rates and the variability of this component
consistently greater than zero (based on the WHO
in human milk, the presumption of its use and
pooled breastfed data set) (Table 7) until the fourth
significance to infant nutrition appears tenuous. The
month when the mean declined to slightly below zero.
decision was thus taken not to include it further in the
Later, Heinig et al. (45) evaluated a sample of breastfed
above calculations.
infants from 0 to 12 months of age enrolled in the
DARLING Study. Protein intakes of breastfed infants
It is possible to estimate the prevalence of inadequacy
at 3 months were comparable to those reported by Butte
from these data using the probability approach that was
et al. (1.1 ± 0.22 g/kg per day), and they remained at
taken in the 1996 IDECG report. A requirement of
approximately 1.1 ± 0.3 g/kg per day through 6 months
approximately 170 mg N/kg, which is close to the
of exclusive breastfeeding. Weight-for-age Z-scores were
report’s “Model C”, yielded a population inadequacy
between 0.5 and 0 for the first 6 months of life (59).
prevalence of approximately 8%.
Two other studies, also conducted in developed
countries, reported that after the first 2 to 3 months
3.2.5 Protein intake and growth
breastfed infants gained weight less rapidly than
Butte et al. examined the adequacy of protein intake
formula-fed infants (60, 61). In both studies infants were
from human milk by determining protein intakes and
not exclusively breastfed and there was a significant drop
growth of exclusively breastfed infants from middle to
(17.5 to 45%) in sample size over time. The unstable
upper economic groups in Houston, TX (16, 58).
anthropometric Z-scores in both studies are thus difficult
Protein intake was 1.6 ± 0.3 g/kg per day at 1 month
to evaluate.
and 0.9 ± 0.2 g/kg per day at 4 months of age. The mean
20

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
Similarly, results from developing countries are incon-
are no data to evaluate the protein adequacy of exclusive
sistent. Although protein intakes of exclusively
breastfeeding at later ages (45, 62), and one may well
breastfed Mexican infants were comparable to those of
ask whether any of the published studies have sufficient
American infants (1.2 ± 0.3 g protein per kg/day at
power to detect physiologically relevant differences in
4 months and 1.1 ± 0.3 g/kg per day at 6 months), their
growth. However, the formula study described above
weight and length velocities were significantly lower
suggests that protein should not be the limiting factor.
than those observed in American infants by 6 months
Some concerns may be raised by the seemingly
of age (20). Weight velocity declined from 16.1 ± 3.2
conflicting data of Butte et al. from Mexico (20) and
g/day at 4 months (Z = approximately 0.2, using boys)
Dewey et al. from Honduras (63). Each of the reports is
to 8 ± 3.5 g/day (Z = approximately –1.25, using boys)
based on infants from low socioeconomic status settings.
at 6 months, and length velocities from 1.92 ± 0.22 cm/
Data from Butte et al. may reflect the insufficiency of
month (Z = −0.25, using boys) to 1.02 ± 0.34 cm/month
exclusive or predominant breastfeeding for sustaining
(Z = −0.75, using boys) (20).
normal growth rates in harsh settings. On the other
In contrast, a sample in Honduras of exclusively
hand, data from Dewey et al. may reflect the reality
breastfed infants were assigned randomly at 4 months
that, under the circumstances, exclusive breastfeeding
either to continue exclusive breastfeeding until
is “as good as” what is achievable in terms of growth.
6 months or to receive a high-protein complementary
However, the period over which weight gain is
food from 4 to 6 months. After 4 months of age, the
calculated may influence this conclusion. Dewey et al.
mean protein intake (g/kg per day) in the group of
(63) reported a weight gain of 1017 g – or the equivalent
infants who received solid food was 20% higher than
of approximately 14.5 g/day – in the exclusively
that of the exclusively breastfed group. Despite these
breastfed group, and 1004 g, or 14.3 g/day, in the
differences in protein intake, no differences from 4 to
supplemented breastfed group between 16 and 26 weeks
6 months in weight or length gain were noted between
of age. Although weight gains over the entire period
feeding groups. Furthermore, 20 infants with the highest
were not discernibly different between groups, weekly
protein intakes were matched to 20 exclusively breastfed
weight gains cannot be calculated or assessed. In
infants with similar energy intakes. Although protein
contrast Butte et al. evaluated specific weight gains
intake was 33% higher in the non-exclusively breastfed
(16.7, 12.3 and 7.8 g/day at 4, 5 and 6 months, respec-
group, growth rates were similar (5). These negative
tively) and noted a downward trend in predominantly
findings should be interpreted cautiously because of the
breastfed infants (20).
precision of the balances used (accurate to 100 g)
relative to the changes in weight observed between 4
and 6 months; and because earlier findings by the same
3.2.6 Plasma amino acids
group documented a positive correlation between
Postprandial concentrations of plasma amino acids also
weight gain and protein intake (39) when intakes and
have been used as an index of the adequacy of protein
weight gain of both breast- and bottle-fed infants were
intakes (64). We were unable to find any data evaluating
examined but no such correlation when only breastfed
changes in plasma amino-acid patterns in exclusively
infants were considered.
versus partially breastfed infants during the first year of
In an experimental study (62), the growth of infants
life.
after 6 months receiving formulas with varying protein
concentrations (13, 15 and 18 g/l) was compared to the
3.2.7 Immune function
growth of exclusively breastfed infants from 0 to
6 months. Breastfed infants from the DARLING Study
Protein undernutrition adversely affects immune
were used as the comparison group (59). Although
function. Protein-deficient infants present impaired
energy intakes were similar in all groups, protein intakes
immune responses that, in turn, increase their risk of
were significantly lower at 6 months of age in the
infectious episodes (65).
breastfed group compared with those of the three
Two papers have been published regarding the associa-
formula-fed groups. Increments in weight and length
tion between protein intake and immune function in
between 4 and 8 months were similar in the formula-
breastfed infants. In one study infants were classified at
fed and breastfed groups (62).
birth as breastfed or formula-fed according to maternal
It thus appears that human milk meets the protein needs
choice (66). Formula-fed infants were assigned
for growth of infants between 0 and 6 months. There
randomly to either a low- or high-soy protein formula,
21

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
or to a cow’s milk-based formula adapted to European
are met at all ages requires improved understanding of
Society of Paediatric Gastroenterology (ESPGAN)
the efficiency of human milk nitrogen utilization (both
recommendations (i.e. a whey:casein ratio of 50:50).
protein and NPN), improved methods for estimating
Infants received the polio immunization and the triple
obligatory needs and better functional measures of
vaccine against diphtheria, pertussis and tetanus (DPT)
nitrogen adequacy.
at 2 and 4 months of age. Blood antibodies were ana-
lysed at 5 and 8 months. Results were consistent with
those reported in the previous study, i.e. infants fed on
3.3 Vitamin A
the low-protein cow’s milk- and soy-based formulas
3.3.1 Introduction
presented poorer antibody responses than did infants
who received the high-protein cow’s milk-based
Vitamin A is a generic term for a group of retinoids
formula. Infants consuming the adapted formula had a
with similar biological activity. The term includes
higher initial antibody response, which was not
retinal, retinol, retinoic acid and substances considered
sustained. Five-month-old exclusively breastfed infants
to be pro-vitamin A because they can be transformed
presented sustained antibody responses that were similar
into retinol. Among the pro-vitamin A compounds,
to those of the high-protein group (66). In another study,
β-carotene has the highest potential vitamin A activity.
breastfed infants from Sweden presented significantly
Recent recommendations by the United States Food
higher faecal titres of both IgA and IgM antibodies, as
and Nutrition Board re-evaluated conversion equiva-
well as the secretory component to poliovirus and
lency and recommended use of 1/12 retinol equivalents
diphtheria and to tetanus toxoid than did infants
(RE) from a mixed diet.
receiving a formula with 1.1 or 1.5 g protein per 100 ml
Retinols are stored in the liver as esters, and storage
(67).
increases in the fetal liver during late gestation. The
The interpretation of the functional significance of
placenta regulates the passage of a sufficient amount of
these observations remains difficult without robust
vitamin A from mother to fetus to meet physiological
comparisons of morbidity in exclusively, predominantly
requirements but not to build up a substantial body
and partially breastfed infants 4 to 12 months old in
reserve. This tight regulation is believed to result in
diverse settings.
low hepatic reserves of vitamin A at birth, even in
infants born to well-nourished mothers, compared to
levels achieved in later life stages (71, 72). After birth,
3.2.8 Infant behaviour
vitamin A is transferred to the infant through human
milk.
Several authors have reported better cognitive develop-
ment and intelligence quotients in breastfed infants
The vitamin A content of human milk depends on
compared with those who are formula-fed (68, 69). A
maternal vitamin A status. Infants of women with
review by Pollitt et al. (70) amply demonstrates the
inadequate vitamin A status are born with low reserves
complexities related to this issue and the difficulties
of vitamin A, and thus their vitamin A status is likely
presented by available studies because of their inability
to be protected for shorter periods than the status of
to distinguish among competing hypotheses. No studies
infants born with higher reserves. Since most vitamin
were found that assess the behavioural outcomes of
A for tissue reserves is transferred late in gestation,
feeding healthy term infants diverse levels of protein
preterm infants have lower stores than full-term infants.
during the first year of life.
In populations that are at risk of vitamin A deficiency,
the age at which a deficiency occurs is related to the
age of weaning, i.e. the shorter the duration of breast-
3.2.9 Summary
feeding, the earlier the onset of deficiency (73). This is
Based on factorial and balance studies, infants’ mean
likely due to the combined effect of the consumption
protein requirements are approximately 1.1 g/kg per day
of complementary foods that are low in vitamin A and
from 3 to 6 months of age. “True protein” provided by
higher vitamin A utilization rates imposed by more
human milk is sufficient to meet the mean protein
frequent infections.
requirements of infants for the first 2 months of life,
and “true protein” intake plus free amino acids and other
3.3.2 Vitamin A in human milk
forms of NPN are likely sufficient to meet the needs of
most, though not all, infants after 4 months. A more
The mature milk of well-nourished mothers contains
precise estimate of the proportion of infants whose needs
approximately 1.7 moles/l vitamin A (6). In addition,
22

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
human milk contains carotene that may contribute to
is relevant for breastfed infants since the bioavailability
the vitamin A transferred to the infant (57) and bile
of preformed vitamin A from human milk is likely to
salt-stimulated lipase, which facilitates the infant’s
be greater than 90%, and breastfed infants are protected
absorption of vitamin A and precursor carotenoids (74).
against infection, particularly gastrointestinal
infections. The potential vitamin A activity of vitamin
Because the vitamin A content of human milk is
A precursors in human milk is not known. Thus, in
strongly influenced by maternal nutritional status, it is
children younger than 1 year, retinoid requirements
not surprising to find lower amounts of vitamin A in
have been based on the estimated intakes of this vitamin
human milk in regions were undernutrition is
by breastfed infants (6). However, the dependence on
widespread and mothers consume vitamin A-containing
maternal diets of human milk vitamin A levels makes
foods less frequently than women in privileged
accurate estimates of requirements difficult to calculate
environments. Consequently, the concentration of
from milk composition data alone.
vitamin A in mature milk of women in underprivileged
countries may be extremely low. For example, Muhilal
The recommended vitamin A intake level for infants
et al. (75) reported baseline values of 0.60 ± 0.29 moles/
0 to 6 months was set at 1.4 µmoles/day and 1.75 µmoles/
l in studies conducted in Indonesia.
day for infants 6 to 12 months based on the intakes of
breastfed infants of well-nourished women (6). A
Vitamin A concentrations vary with the stage of
deficiency state has been defined as stores that are
lactation. In a cross-sectional study in Guatemala,
insufficient to maintain optimal vitamin A concen-
vitamin A concentrations in milk of low-income women
trations in target tissues. This is generally observed when
decreased from 1.40 µmoles/l at 6 months of lactation
body stores fall below 0.07 moles/g liver (81). Serum
to 1.33 and 1.26 µmoles/l at 9 and 15 months,
retinol levels and the relative dose-response test have
respectively (76). In the Philippines concentrations
been used to assess hepatic vitamin A stores, but other
decreased from 1.26 µmoles/l at 3 months to 0.88 µmoles/
functional measures of vitamin A status, e.g. ocular
l at 9 months of lactation (76). Similarly, lactating
manifestations, are used more often in practice. Less
Ethiopian mothers presented vitamin A concentrations
specific measures of vitamin A status such as growth
of 1.16 ± 0.52 µmoles/l at 1.5–3.5 months of lactation,
retardation, increased susceptibility to infections and
and 0.74 ± 0.25 µmoles/l at 11.5–23.5 months of
greater mortality risk are also occasionally used (82, 83).
lactation (77).
According to Stoltzfus & Underwood (73), the best evi-
dence that vitamin A levels in human milk correspond
3.3.4 Plasma retinol
to maternal vitamin A status is the improved concen-
Serum retinol levels in individuals are tightly regulated;
trations in milk after maternal supplementation in areas
for the reasons outlined above, however, they are
where vitamin A deficiency is endemic (75, 78–80).
indicative of vitamin A status in individuals only when
body reserves are depleted or surpassed. Fortunately,
3.3.3 Estimates of vitamin A requirements
serum vitamin A distribution curves and population
dietary intake patterns can be used to assess and compare
The vitamin A requirements of infants are difficult to
the vitamin A status of populations (83). However,
estimate accurately because of the lack of a sensitive
interpretation of serum retinol levels can be confounded
index of vitamin A status. Plasma retinol levels are
by stress, which reduces levels on an acute basis,
insensitive to the adequacy of intake until hepatic stores
resulting in abnormally high prevalence rates of poor
are severely depleted. Other methods that have been
vitamin A status.
considered to assess vitamin A status include adaptation
At birth, serum vitamin A concentrations in term
to darkness, the pupillary response test, total liver
infants of well-nourished mothers are approximately
reserves by isotope dilution, relative dose response/
0.70 µmoles/l or greater (84, 85). In contrast, serum
modified relative dose response, conjunctival impression
vitamin A levels of infants born to mothers with
cytology and immune function (6). However, none of
marginal vitamin A status are reported at approximately
these methods is completely suitable for assessing the
0.49 µmoles/l (86). In Indonesia more infants whose
vitamin A requirements of infants.
mothers had vitamin A concentrations below 1.4 µmol/l
Intestinal absorption is among the dietary factors that
in their milk had evidence of depleted liver stores and
influence vitamin A requirements. In turn, dietary fat,
had lower serum retinol concentrations than did infants
infections, the food matrix and food processing all affect
whose mothers’ vitamin A milk concentrations were
intestinal absorption (6). However, none of these factors
above this value (80).
23

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
WHO and UNICEF use a mean population value of
upper arm circumference and triceps skin-fold in
0.7 µmol/l to identify subclinical vitamin A deficiency
children under 3 years of age with xerophthalmia than
in populations, but they caution that this value may
in controls. Vitamin A-deficient children consumed
not identify deficient individuals (87). None the less,
almost half the amount of vitamin A-containing foods
this value is commonly used to describe the status of
(dark-green leafy vegetables and milk) than controls
both populations and individuals and to characterize
(91). In another study, also conducted in Indonesia by
responses to interventions designed to improve vitamin
the same group, children who spontaneously recovered
A status. For example, the mean serum retinol levels of
from xerophthalmia were compared to a group of
6-month-old exclusively breastfed Bangladeshi infants
children who did not recover spontaneously and to a
was 0.77 ± 0.21 µmol/l. Thirty-four per cent presented
group of healthy children. Weight and height were
levels below the 0.70 µmol/l cut-off (88). Serum levels
evaluated at 3-month intervals. Infants who recovered
were 0.84 ± 0.23 µmol/l (89) in a similar group of infants
spontaneously gained weight at the same rate as healthy
whose mothers were supplemented postnatally with
infants, but their height deficits persisted. Infants who
vitamin A, but 25% of the infants in this group were
did not recover, and those who became xerophthalmic
reported to have serum values below 0.7 µmol/l. The
during the follow-up period, presented the greatest
vitamin A content of human milk in these populations
weight and height deficits (92). Although such
was 0.87 ± 0.61 µmol/l in unsupplemented women and
descriptive data are interesting, they are difficult to
0.85 ± 0.53 µmol/l in women supplemented with
interpret because it is likely that all subjects suffered
vitamin A.
from multiple nutrient deficiencies.
A mean serum retinol concentration of 0.67 µmol/l was
However, intervention trials that examined the effect
reported in 1.5-month-old infants in a multicentre trial
of vitamin A intake on growth also present difficulties,.
conducted in Ghana, India and Peru. Levels below 0.70
In a randomized, placebo-controlled study conducted
µmol/l were reported for 63% of those infants (90). The
in India, supplementing infants for 1 year with weekly
administration of 25 000 IU of vitamin A with each of
doses of 2500 µg (8.8 moles) vitamin A and 20 mg
the first three doses of DPT/poliomyelitis immunizations
vitamin E failed to improve growth (93). This occurred
resulted in mean serum vitamin A levels of 0.84 µmol/
despite a higher mortality rate in the placebo group,
l in these groups at 6 months of age, and the percentage
suggesting a beneficial effect of vitamin A supplemen-
of infants with retinol levels below 0.70 µmol/l decreased
tation. Failure to see a growth response suggests that
to 30% by 6 months. However, the average retinol
either the level of vitamin A provided was insufficient
concentration 0.80 µmol/l and the percentage of infants
to achieve normal growth or other nutrient levels were
with retinol levels below 0.7 µmol/l also dropped (37%)
more limiting with respect to growth. In another
in the placebo group included in that trial (90). Of 339
randomized study conducted in Indonesia, children
infants 77% had abnormal relative dose response tests
received 60 000 µg (210 moles) retinol or a placebo on
at 1.5 months of age. The percentages with abnormal
two occasions within 1 year. Supplementation improved
tests declined to 43%, 38% and 28% at, respectively, 6,
weight gain only in males 24 to 60 months of age and
9 and 12 months following the administration of
had no effect in males or females younger than 24
months (94). Similarly, in another Indonesian trial,
vitamin A. Parallel declines were observed in the
commercial monosodium glutamate was fortified with
placebo group (90). The relative vitamin A concen-
vitamin A. Fortification resulted in improved linear
trations in milk were similar for both the treatment and
growth, but this time only in children 12 to 24 months
placebo groups.
old (75).
A more recent trial by the same group in Indonesia
3.3.5 Functional end-points
controlled for baseline vitamin A status. Children were
Growth and vitamin status
supplemented randomly with vitamin A (103 000 to
206 000 IU, according to age) or a placebo. Results were
Associations between linear growth retardation and
adjusted by the children’s pre-treatment vitamin A
vitamin A deficiency have been found in some, but not
status. An improvement in linear growth (0.16 cm),
all, studies. In a community-based study conducted in
but not in weight, was observed after supplementation
Indonesia, 466 children were identified as vitamin A-
in children older than 24 months. After adjusting for
deficient (presence of night blindness, Bitot’s spots or
pre-treatment vitamin A status, supplemented children
xerophthalmia). Age-specific paired comparisons
with serum retinol < 0.35 µmol/l at baseline grew
showed a lower height-for-age, weight-for-height, mid-
0.39 cm and gained 152 g more weight in a period of
24

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
16 weeks than children in the placebo group. Weight
greater in vitamin A-deficient infants and their
and height gains were not different between treatment
requirements for vitamin A are higher.
groups in children with retinol concentrations above
Evidence for these associations comes from different
0.35 µmol/l (95). Levels of vitamin A in human milk
types of studies. For example, in South Africa 10-month-
for the various groups were not reported.
old infants hospitalized with complicated measles and
Thus, an effect of supplementation with vitamin A on
supplemented with a single dose of 400 000 IU vitamin
growth may be observed in a group of children with a
A recovered more rapidly from pneumonia and
high likelihood of deficiency, but apparently not in
diarrhoea than the placebo group (99). In Bangladesh,
infants, i.e. 0 to 12 months of age. The above-mentioned
infants of vitamin A-supplemented mothers had
multicentre randomized and placebo-controlled study
significantly shorter episodes of respiratory tract
conducted in Ghana, India and Peru followed infants
infections and fewer febrile episodes in the first 9 months
until 12 months of age. No difference in weight and
postpartum than infants of unsupplemented mothers
length gain or Z-scores was observed between supple-
(79). In contrast, after controlling for age and
mented and placebo groups despite the high percentage
nutritional status, smaller but frequent doses of vitamin
of infants with vitamin A deficiency as determined by
A supplements provided Indian infants 6 to 60 months
serum retinol and relative dose response (90). Thus, it
of age (2500 µg weekly) had no effect on the incidence,
is possible that factors other than vitamin A status are
severity or duration of diarrhoea or respiratory tract
more sensitive determinants of growth in infants in this
infections (93). Similarly, in the above-mentioned
age group. Indeed, in a study conducted in Egypt, the
multicentre study conducted in Ghana, India and Peru
growth of sick and healthy infants was compared after
no differences in the prevalence of diarrhoea and acute
supplementing their mothers with vitamin A. Milk
lower-respiratory infections were noted between placebo
retinol levels correlated significantly with the growth
and supplemented groups (90). In Indonesia, a placebo-
of healthy infants, but not with those who were ill (96).
controlled trial was conducted in 2067 neonates who
received either 50 000 IU vitamin A orally or a placebo
on the first day of life. The vitamin A supplement
Ocular manifestations
reduced the infant mortality rate and the prevalence of
severe respiratory infection (100). Vitamin A
In Malawi 152 children with xerophthalmia were
supplementation at birth reduced the risk of
compared to 151 age-matched children without visual
pneumococcal colonization in South Indian infants
manifestations of vitamin A deficiency. Weaning was
(101).
initiated and breastfeeding stopped significantly earlier
for children with xerophthalmia than for healthy
The effect of vitamin A supplementation on mortality
children (97). However, in another study conducted in
rates is also somewhat inconsistent. A recent review by
Indonesia more than 90% of the children, with or
Villamoor & Fawzi (102) summarized various issues
without xerophthalmia, were breastfed for at least 12
related to vitamin A sufficiency. The authors reviewed
months, and the duration of breastfeeding was similar
the inconsistent results of community-based trials
between infants with xerophthalmia and controls.
targeting infants older and younger than 6 months.
Although the age of introduction of solid foods was not
Although supplementation of deficient populations
investigated, infants with xerophthalmia received
generally appears to decrease mortality, this outcome
significantly less vitamin A-rich foods than did controls.
has not always been observed. The inconsistency in
This suggests that in some settings the quality of
results is ascribed to multiple factors that include
complementary foods plays as important a role as the
interactions among multiple but variable nutrient
duration of breastfeeding (91).
deficiencies, other population-specific characteristics,
and magnitude and frequency of supplementation (102).
Morbidity and mortality
Mortality risks have been reported to be 30–60% higher
in children with keratomalacia and xerophthalmia than
High morbidity and mortality rates due to infectious
in healthy populations (103). Most studies have
diseases are associated with clinical and subclinical
reported reductions in mortality rates in preschool
vitamin A deficiency. Moreover, it has been reported
children after vitamin A supplementation (99, 75, 104,
that during infectious episodes vitamin A is excreted
103). However, other supplementation studies have
in urine at higher levels than usual (98). Thus, the risk
failed to observe protective effects (105, 106). Two
of increased frequency and severity of infections is
meta-analyses that included the above-cited studies
25

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
concluded that supplementation reduced mortality in
3.4 Vitamin D
preschool children (107, 108). However, more recent
3.4.1 Introduction
studies failed to observe similar protective effects. In
Nepal, differences in mortality rates were not noted in
Vitamin D is a fat-soluble vitamin that is synthesized
infants, from 0–5 months of age, who received a single
in the skin and may be obtained from the diet. There
dose of 15 000 to 30 000 IU of vitamin A or a placebo
are two forms: vitamin D2 (ergocalciferol) and vitamin
(109). Cumulative morbidity and mortality rates were
D3 (cholecalciferol). Vitamin D2 originates from
similar between supplemented and placebo groups from
ergosterol, a plant sterol, and is obtained through the
1 to 12 months of age in the Ghanaian, Indian and
diet; vitamin D3 originates from 7-dehydrocholesterol,
Peruvian multicentre trial (90).
a precursor of cholesterol. Both vitamins D2 and D3
require one hydroxylation in the liver to 25-hydoxy-
Studies of this type suggest several possibilities. Either
vitamin D and another in the kidney to form the
present cut-offs used to assess vitamin A adequacy
biologically active hormone, 1,25-dihydroxyvitamin D
should not be used as proxies for increased risk of
(1,25 (OH)
morbidity and mortality in all infants; or inadequate
2D).
vitamin A status of young infants in some study
Receptors for 1,25 (OH)2 D are found in the small
populations is not a major risk to increased morbidity
intestine and other tissues such as the brain, pancreas
or mortality; or inadequate vitamin A status acts in
and heart. Anti-proliferation and pro-differentiation
concert with other factors in a way that requires their
functions have been suggested for vitamin D (110).
simultaneous correction before expected benefits can
Receptors for 1,25 (OH)2 D have been detected in the
be achieved.
small intestine and colon of the human fetus (110),
which suggests that vitamin D has an important role in
cell differentiation during gestation (111). In postnatal
3.3.6 Summary
life, the most widely recognized functions of vitamin D
are related to calcium and phosphate metabolism.
The absence of any evidence of vitamin A deficiency
in well-nourished populations suggests that the vitamin
A content of human milk is adequate to meet the
3.4.2 Factors influencing the vitamin D content of
vitamin A requirements for infants during the first
human milk
6 months of life when mothers are well nourished.
However, it is important to recall that there are no
It is widely accepted that human milk contains very
population assessments of the vitamin A status of
low levels of vitamin D (Table 8). Vitamin D concen-
exclusively breastfed infants beyond this age. Human
trations in human milk depend on maternal vitamin D
milk is the primary source of vitamin A in environments
status (112). Factors affecting vitamin D status include
where vitamin A deficiency is prevalent, and in these
skin pigmentation, season and latitude (113). Increased
settings the population of breastfed infants with
skin melanin concentration reduces the efficiency of
deficient or marginal vitamin A stores appears to be
vitamin D synthesis in the skin. Thus, individuals with
significant from a public health perspective. None the
dark skin and limited sun exposure are at greater risk of
less, the lower risk of xerophthalmia and mortality
inadequate vitamin D synthesis than those with less skin
observed in breastfed infants compared to their non-
pigment. Although the vitamin D2 and D3 content in
breastfed counterparts argues strongly in favour of
the milk of dark-skinned women may be lower than
continued breastfeeding. This difference is likely to be
that of light-skinned women, maternal serum 25(OH)D
the result of inappropriate complementary foods and
levels can nevertheless be similar in both groups (114).
heightened vitamin A requirements due to high rates
However, these findings are not consistent with an
of infection in prematurely weaned infants. Also, based
earlier report by Specker et al. (115) of lower 25(OH)D
on the available evidence, it is not possible to make a
in the milk and maternal serum of dark-skinned than
case for exclusive over predominant breastfeeding unless
light-skinned women and a significant correlation
one argues that all supplementary feeding decreases milk
between maternal 25(OH)D in serum and milk. The
intake and thus, in these settings, also diminishes
vitamin D in milk of mothers who deliver in the late
vitamin A intakes.
autumn or winter at or above 40°N latitude or below
40°S latitude comes only from dietary sources or stores
because there is hardly any synthesis in the skin at these
times of the year (116). Thus, the vitamin D content of
the milk of women living at these latitudes can be reduced.
26

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
Table 8. Vitamin D content of human milk
Milk
Vitamin D
Stage
Vitamin D
concentration
activity
of
Milk
Reference
N
Country
status
(µg/l)
(IU)
lactation
sample
Hollis et al. (120)
5
Canada
Normal (NS)
0.39 ± 9
25
1–21 days
Whole milk
Leerbeck & Sondergaard (233)
2
Europe
15
Pooled
Lipid fraction
Reeve et al. (234)
3
USA
Normal (S)
0.16
53
Mid-lactation
Bawnik et al. (119)
5
Israel
Unknown (NS)
0.37 ± 0.03
15
3–21 days
Whole milk
0.35 ± 0.07
15
pooled
Zoeren-Grobben et al. (235)
8
Netherlands
Healthy (NS)
1.5 ± 6
1–8 months
Lipid fraction
NA
Abbreviations:
NS = non-supplemented
S = supplemented with vitamin D
NA = not available.
Since it is not easy to obtain preformed vitamin D from
normal vitamin D status is most evident when one
the diet – it is found in only a few food sources such as
considers that approximately 6 litres of human milk
egg yolk, liver and fatty fish – maternal vitamin D status
daily would be necessary to obtain the minimal amount
is most often a function of sun exposure. The conse-
of vitamin D needed to prevent rickets where sun
quences of this relationship can be highly significant.
exposure is inadequate. Two hours is the required
For example, 70% of the women of upper socioeconomic
minimum weekly amount of sunlight for infants if only
class and their exclusively or predominantly breastfed
the face is exposed, or 30 minutes if the upper and lower
infants studied in Pakistan were reported to be vitamin
extremities are exposed. Breastfed infants who are
D deficient (117). These findings suggest that vitamin
exposed to less sunlight present low 25(OH)D serum
D activity in human milk can be increased by maternal
concentrations (115). Because of the normal depen-
supplementation with preformed vitamin D (118–121,
dence on sunshine for vitamin D adequacy, it is not
112). Ala-Houhala et al. (118) reported that the
currently possible to provide precise estimates of vitamin
administration of 2000 IU of vitamin D to breastfeeding
D requirements.
women normalized their infants’ 25(OH)D levels. A
lower dose of 1000 IU was not effective in this regard.
Yet, it is difficult to understand the rationale for
Level of vitamin D intake and serum 25(OH)D
supplementing women to correct their infants’ vitamin
Serum 25(OH)D is considered the best indicator of
D status, unless maternal supplementation is also used
vitamin D status because it reflects the combined
as a strategy to increase maternal vitamin D stores in
vitamin D obtained from diet, sunlight and liver stores
preparation for a subsequent pregnancy, or to correct or
(123, 124). The cut-off for defining vitamin D
avoid other maternal vitamin D abnormalities.
deficiency in adults is based on the level of serum
25(OH)D below which high serum parathyroid
hormone (PTH) concentrations are observed (122).
3.4.3 Estimates of vitamin D requirements
However, a cut-off based on PTH has not been
The United States Food and Nutrition Board (122)
determined for infants. The current cut-off of 27.5 nmol/
recommends 5 g of vitamin D for infants 0 to 6 months
l for infants is based on serum 25(OH)D levels observed
of age, although it also acknowledges that breastfed
in cases of vitamin D deficiency rickets. It is also
infants “with habitual small doses of sunshine” do not
important to note that although there are significant
require supplemental vitamin D. Infants in far northern
correlations between milk and maternal serum
latitudes or those with minimal sunlight exposure
25(OH)D levels, no such associations are reported
require a minimum of 2.5 µg/day (100 IU) to prevent
between milk vitamin D and infant serum 25(OH)D.
rickets.
This is likely a reflection of the infant’s endogenous
synthesis of vitamin D (112).
The physiological dependence on ultraviolet light for
27

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
Table 9. Vitamin D status of breastfed infants
Age and
Serum
duration of
Vitamin D
25 (OH) D
Reference
N
Country
supplementation
Supplement
(ng/ml)
BMC
Growth
Roberts et al. (129)
22
USA
14 days
0
17 ± 3
Normal in
Normal
19
14 days–4 months
400 IU
22 ± 3
all groups
Markestad et al. (130)
7
Norway
9–12 months
0
50% with
Dropped at
less than
6 months from
11 ng/ml
60th to 40th
percentile
Greer & Marshall (128)
24
USA
0–7 days
0
Dropped at
22
(Caucasian)
0–6 months
400 IU
1.5 months
Normal
Chan et al. (125)
22
USA
Birth
0
19 ± 2
Normal in
Normal in
29
(Caucasian)
0–6 months
400 IU
23 ± 3
all groups
all groups
Feliciano et al. (144)
255
China
3–5 days
100 IU
Normal in
0–6 months
200 IU
all groups
300 IU
Fomon et al. (145)
26
USA
8 days
300 IU
Normal in
11
(Caucasian)
0–6 months
400 IU
all groups
13
1600 IU
Atiq et al. (141)
38
Pakistan
< 6 months
0
34 nmol/l
24
> 6 months
Specker et al. (133)
52
China
3–5 days
100 IU
8 ± 13
Normal in
52
(North)
0–6 months
200 IU
6 ± 9
all groups
52
400 IU
11 ± 10
Abbreviations:
BF = breastfed
BMC = bone mineral content
S = supplemented with vitamin D
Breastfed infants in regions where sunlight is plentiful
and 25(OH)D and high PTH). Infants who received
have adequate serum concentrations of 25(OH)D before
the higher dose achieved normal serum 25(OH)D and
6 months of age (125–129, 115). In contrast, infants
PTH concentrations in the first month with no further
less than 6 months of age living in regions where
changes in either 25(OH)D or PTH. Infants who
sunlight exposure is minimal have serum 25(OH)D
received the lower dose also had increased 25(OH)D
concentrations within ranges typically observed in cases
concentrations and decreased PTH levels. Although
of rickets (130–133) (Table 9).
PTH and 25(OH)D levels were within the normal range
by the end of the first month in infants who received
500 IU/day of supplementary vitamin D, PTH and
Other biochemical and clinical parameters associated
25(OH)D levels continued to change through the third
with vitamin D deficiency
month, approaching levels in infants supplemented at
Decreases in the serum concentrations of phosphorus
the higher dose. In the control group with normal serum
and increases in PTH are early signs of vitamin D
calcium, 25(OH)D and PTH concentrations presented
deficiency. Decreases in serum calcium are observed only
only slight increases in 25(OH)D (15 nmol/l); PTH
in very severe cases. Zeghoud et al. (134) evaluated
concentrations remained stable. All three groups were
responses to either 500 IU/day or 1000 IU/day of
fed a formula containing 400 IU/l of vitamin D. Thus,
supplementary vitamin D in 42 infants born with
the authors concluded that infants born with subclinical
subclinical vitamin D deficiency (low serum calcium
vitamin D deficiency can require higher vitamin D
28

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
intakes in early life than those born with more adequate
bourhood conditions that prohibit outdoor activities,
stores (134).
placed at risk infants of middle and lower socioeconomic
groups.
Clinical manifestations of severe vitamin D deficiency
include hypocalcaemic seizures. A study in the United
However, other studies have failed to identify breastfed
Kingdom of Great Britain and Northern Ireland of 2-
infants with rickets despite low 25(OH)D serum
to 14-month-old infants born to parents of Pakistani
concentrations. For rickets to develop, sustained low
origin presented with hypocalcaemic seizures and were
25(OH)D concentrations for long periods are probably
found to be vitamin D deficient. The diagnosis was based
necessary. In a study conducted in northern China
on high concentrations of alkaline phosphatase and low
(40 to 47°N latitude) approximately 33% of the breast-
concentrations of serum 25(OH)D, loss of metaphyseal
fed infants presented 25(OH)D concentrations below
definition and a positive response to vitamin D
11 ng/ml, and this despite supplements of 2.5 to 5 µg
supplementation (117).
(100 to 200 IU) of vitamin D (133). In the Republic of
Korea 97% of breastfed infants born during winter and
47% born during summer were reported to be vitamin
Bone mineralization
D-deficient (131). In Pakistan, 55% of breastfed infants
Severe vitamin D insufficiency results in inadequate
presented with vitamin D serum concentrations below
mineralization of the skeleton. In growing infants
10 ng/ml (141). In the USA Greer & Tsang (142)
deficient mineralization leads to rickets, a disease
reported that exclusively breastfed 6-month-old infants
characterized by a widening of the ends of long bones,
presented with very low 25(OH)D serum concen-
deformation of the rib cage (rachitic rosary), and limb
trations, but none in any of these populations presented
deformations such as bowed legs and knocked knees.
with rickets.
Studies of subclinical vitamin D deficiency and its effects
Thus, although there is abundant evidence suggesting
on bone mineralization are inconsistent, and this likely
that breastfed infants often receive less vitamin D than
reflects both the differential effects of PTH on cortical
is required, most studies fail to find rickets in breastfed
and trabecular bone and the ability of various
infants less than 6 months of age. However, this
measurements to distinguish such effects. Primary
conclusion is tempered by studies of older infants. In
hyperthyroidism decreases cortical bone mineral density
1979 Bacharach et al. reported rickets in breastfed
(BMD), and either it has no effect on, or it increases,
infants older than 6 months whose mothers were
trabecular BMD (135, 136). In a study of exclusively
vitamin D-deficient during pregnancy and lactation
breastfed infants in the USA, 400 IU of supplemental
(139). In 1980, 9 cases of rickets were reported in
vitamin D prevented a decline in bone mineralization
Chicago in exclusively breastfed infants aged 7 to 24
at the distal radius that has been observed in infants
months (140). None of the infants received any food
administered a placebo (126). However, Specker et al.
from animal sources. Thirty children (median age 15.5
did not observe rickets at 6 months of age in any of 256
months) were diagnosed with rickets in North Carolina.
breastfed infants enrolled in a randomized, double-blind
All were African American and were breastfed for a
controlled study in China that provided either 100 IU,
median duration of 12.5 months with no vitamin D
200 IU or 400 IU of vitamin D per day (133). This
supplements (143).
study found supplementation with 100 IU to be
sufficient to prevent rickets in breastfed infants with
It thus seems that infants who are exclusively or
limited sun exposure and vitamin D stores.
predominantly breastfed for 6 months or longer can be
at an increased risk of rickets if their mothers are at risk
of vitamin D deficiency, and the infants receive limited
3.4.4 Vitamin D status and rickets
sun exposure and no vitamin D supplements.
In 1925 Elliot reported a large number of breastfed
infants with rickets in poor urban areas of the USA.
3.4.5 Vitamin D and growth in young infants
Rickets in breastfed infants also has been reported more
recently in Greece (137), Nigeria (138), Pakistan (119),
The effects of vitamin D on growth in early infancy are
and in the USA, mainly among African American
best evaluated from results of a study conducted in
infants (139, 140). In a study conducted in Chicago,
China of breastfed infants assigned randomly to either
Edidin et al. (140) described the social conditions that
100, 200 or 400 IU of vitamin D per day. The different
can lead to rickets in developed countries. Minimal sun
doses of vitamin D did not affect growth rates of infants
exposure due to protective clothing, or unsafe neigh-
who were born at the same latitude, but significant
29

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
differences were found in length gains over a 6-month
to experience impaired growth unless supplemented
period between infants living in northern or southern
with vitamin D. However, other nutrient deficiencies
China. Length gains were greater in infants born in the
may account for growth retardation.
north independent of supplement level. No seasonal
differences were noted in either the south or the north.
These data suggest that differences (e.g. genetic or
3.4.7 Summary
environmental) other than vitamin D status may have
The vitamin D content of human milk is low and
influenced regional differences in length gain (144).
dependent on maternal vitamin D status as reflected by
maternal serum 25(OH)D. Breastfed infants can
3.4.6 Vitamin D and growth in older infants
maintain normal vitamin D status in the early postnatal
period only when their mothers’ vitamin D status is
The effect of marginal vitamin D status on growth in
normal and/or the infants are exposed to adequate
older infants remains somewhat controversial because
amounts of sunlight. Risk of vitamin D deficiency
of inconsistent findings. On the whole, however, there
increases as infants’ sun exposure decreases, and the
appear to be few data supporting adverse effects on
ability of infants of vitamin D-replete mothers to
growth. Fomon, Younoszai & Thomas (145) reported
maintain normal vitamin D status in the absence of sun
similar growth rates from birth to 140 days among
exposure remains unknown. Infants born at high
infants receiving either a formula supplemented with
latitudes, or in places where sun exposure is restricted
400 or 1600 IU of vitamin D and breastfed infants.
for cultural or other reasons, are at special risk; they are
Breastfed infants were allowed one formula feeding daily
likely to be born with low vitamin D stores due to low
that provided 500 IU of vitamin D/l. Breastfed infants
maternal vitamin D status. If sunlight exposure or
also received a multivitamin preparation containing
exogenous intakes of vitamin D remain inadequate, the
1500 IU vitamin A, 200 IU vitamin D, several of the B
risk of vitamin D deficiency rises with age as stores are
vitamins and ferrous sulphate. Also, infants were
depleted.
unlikely to be born with marginal vitamin D stores. In
another study in the USA of infants less than 1 year of
age, no differences in weight or length were detected
3.5 Vitamin B6
between breastfed infants, breastfed infants supplemen-
3.5.1 Introduction
ted with 400 IU of vitamin D, and infants fed formula
with added vitamin D. However, all mothers in the study
Vitamin B6 functions as a coenzyme in the metabolism
were supplemented with vitamin D while infants were
of protein, carbohydrate and fat. The term refers to
permitted one formula feeding per day during the first
several compounds, e.g. pyridoxal (PL), pyridoxine
4 months, after which solids were added to their diet
(PN), pyridoxamine (PM) and their respective
(125).
phosphate forms – PLP, PNP and PMP. The major forms
of vitamin B6 are PLP and PMP in animal tissues, and
In a series of studies conducted by Brooke et al., slow
PN and PNP in plant tissues. Signs and symptoms of
statural growth was reported in the first year of life in
vitamin B6 deficiency include dermatitis, microcytic
infants who were born to vitamin D-deficient mothers
anaemia, seizures, depression and confusion. In infants
supplemented with vitamin D in the postpartum period
vitamin B6 deficiency appears to adversely influence
(146–148). Greer et al. (127) reported that Caucasian
growth.
infants exclusively breastfed for 6 months in Wisconsin
were 2 cm shorter at 1 year than infants who received
400 IU daily of supplemental vitamin D, although the
3.5.2 Vitamin B6 content in human milk
difference did not attain statistical significance. It is
unclear if there was no difference in attained stature or
The vitamin B6 content of human milk varies with
if failure to detect a difference reflected a lack of
maternal B6 status and intake. The mean B6 concen-
sufficient power in the experimental design. In another
tration in human milk of women with B6 intakes below
study of vitamin D-deficient infants who were
2.5 mg/day is 0.13 mg/l (778 nmol/l). Mean B6 levels
exclusively breastfed for a mean of 7.5 months, length-
in milk of women with B6 intakes between 2.5 and 5
for-age percentiles dropped from 60 to 40 between 6 to
mg/day are substantially higher – approximately 0.24
12 months of age (130). Thus, breastfed infants of
mg/l (149). Thus, the daily B6 intakes of infants 1 to 6
women with poor vitamin D status, or infants with
months of age who consume at least 780 ml/day of
biochemical evidence of vitamin D deficiency, appear
human milk with a B6 concentration of 0.13 mg/l
30

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
should, as expected, meet the 0.1 mg/day estimated
3.5.4 Estimates of requirements
adequate intake (AI) for this age group (150) since the
The AI for vitamin B6 is 0.1 mg/day for infants 0 to
AI was based on B6 intake from human milk.
6 months and 0.3 mg/day for infants 6 to 12 months of
The milk concentration of vitamin B6 in populations at
age (160). The AI for the younger age group is based
risk of vitamin B6 deficiency may be sub-optimal. The
on intakes of exclusively breastfed infants. The AI for
concentration of B6 in the milk of 70 Egyptian women
older infants is based on extrapolations from data
consuming 1.0 mg vitamin B6/day was 0.073 mg/l,
obtained in both the younger age group and adults.
substantially lower than that reported for women in
Western societies (151). Lower concentrations of milk
B6 were associated with lower birth weight and altered
3.5.5 Vitamin B6 status of breastfed infants and
infant behaviour. Thus, human milk’s vitamin B6 content
lactating women
closely parallels the mother’s intake of this vitamin.
Blood PLP concentrations are high in the fetus and
Other factors, e.g. length of gestation, stage of lactation
newborn, and they decrease progressively throughout
and the use of B6 supplements, influence the vitamin
the first year of life (157). Reference ranges for erythro-
B6 concentration in human milk. The vitamin B6
cyte PLP (EPLP) concentrations and erythrocyte
concentrations in milk of women supplemented during
aspartate transaminase (EAST) activities in lactating
lactation with 2 or 27 mg B6/day and who delivered
Finnish women and their infants were established by
prematurely were reported to be 0.05 mg/l and 0.22 mg/
Heiskanen et al. (156). To be included in the reference,
l, respectively. These levels were sustained for 28 days
infants had to be exclusively breastfed for 6 months by
postpartum. Levels in milk of women who delivered at
women with adequate B6 status who were supplemented
term and were supplemented at the same levels were,
with 1 mg PN/day, who fed appropriate complementary
respectively, 0.08 mg/l and 0.38 mg/l during the first
foods after 6 months, and who weaned to a cow’s milk-
week postpartum. Vitamin B6 levels in milk rose to 0.10
based formula at approximately 9 months. The 10th
mg/l and 0.50 mg/l, respectively, by 28 days postpartum
centile values for EPLP concentrations and EAST
(152). Similarly, in a study conducted by Udipi et al.,
activity and activation coefficients were defined based
throughout the first month postpartum vitamin B6
on subsets (n=90 at 2, n=106 at 4, n=99 at 6, n=39 at 9,
levels in milk of women delivering prematurely were
and n=100 at 12 months postpartum) of the original
lower than the levels of women who delivered at term
sample (n=198).
(153). Also analysed was the effect on vitamin B6 milk
In a follow-up analysis, Heiskanen et al. (158) evaluated
concentrations of different levels of supplementation.
the B6 status of 44 infants from the original sample of
Women received 0, 2.5, 10 or 20 mg PN(HCL) for 3
198 who met WHO’s feeding recommendation
consecutive days. Non-supplemented mothers had the
(exclusive breastfeeding for 6 months and continued
lowest vitamin B6 levels in their milk (0.09 ± 0.01 mg/l)
breastfeeding for 12 months with appropriate comple-
compared to the other groups (0.19 ± 0.02 mg/l, 0.25 ±
mentary feeding). Low vitamin B6 status – diagnosed
0.02 mg/l and 0.41 ± 0.04 mg/l, respectively) (154).
as at least two reference values below the 10th centile
cut-offs – was observed in 7 of the 44 infants between 4
3.5.3 Approaches used to estimate vitamin B6
and 6 months of age. Weight velocities of these infants
requirements
did not differ from infants with normal B6 status, but
their length velocity was significantly lower at 6 to
Measurements of vitamin B6 concentrations in plasma,
9 months.
blood cells or urine have been used as indicators of B6
status. Functional indicators such as erythrocyte
The vitamin B6 status of exclusively breastfed infants
aminotransferase saturation by PLP or measurements
was evaluated at 2 months (n=118), 4 months (n=118),
of various tryptophan metabolites also have been
6 months (n=112), 7.5 months (n=70), 9 months
considered as indicators of B6 status in depletion-
(n=36), 10 months (n=14), 11 months (n=11) and 12
repletion studies because of their responsiveness to
months (n=7) (159). During the first 4 months the
changes in B6 intakes. Plasma PLP often has been used
vitamin B6 status of the infants was adequate and
to assess vitamin B6 status because it reflects tissue
independent of maternal status. By 6 months 30% of
stores, responds to changes in dietary B6 and correlates
the infants breastfed by mothers with low vitamin B6
well with other B6 indices (155). However, erythrocyte
status also had low status. By 6 months of exclusive
PLP may be a more reliable indicator, particularly in
breastfeeding, the low vitamin B6 status of mothers was
infants (156).
reflected in the vitamin B6 status of their infants. At 6
31

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
and 7.5 months indicators of vitamin B6 status in
her infant. Compromised linear growth associated with
mothers and infants were significantly correlated.
low vitamin B6 status in infants exclusively breastfed
Despite a daily PN supplement of 1 mg/day, maternal
for 6 months was reversible through appropriate comple-
B6 status was inadequate in ~8% of mothers in the first
mentary feeding. In populations with poor vitamin B6
6 months and in 11% of mothers at 9 months post-
nutriture, the concentration of B6 in human milk will
partum. Prenatal vitamin B6 stores appear important
be sub-optimal, with possible adverse effects on infant
for the maintenance of adequate vitamin B6 status of
growth and neurological development.
breastfed infants in the first 4 months of life. Human
milk alone may not sustain vitamin B6 requirements
beyond 6 months.
3.6 Calcium
3.6.1 Human milk composition
3.5.6 Growth of breastfed infants in relation
Human milk contains 250–300 mg/l of calcium with
to vitamin B6 status
no pronounced changes during lactation (33).
Generally, maternal diet does not appear to influence
In the series of studies conducted by Heiskanen et al.
the concentration of calcium in milk. However, recent
(156, 158, 158) EPLP concentrations at 4 months of
studies from the Gambia indicated that poorly nourished
age correlated positively with length velocity from 0 to
women on low-calcium diets produced milk with lower-
6 months (r=0.46, p=0.006), and EAST activity in the
than-normal calcium levels (161), which did not
entire sample correlated with length velocity and
increase with calcium supplementation (162).
changes in length-for-age at 9 months. Weight velocity
assessed during the entire first year did not differ
statistically among infants with adequate or low B6
3.6.2 Estimates of calcium requirements
indices (n=7). Between 6 and 9 months of age, infants
with low B6 indices experienced slower length velocities
Calcium requirements are affected substantially by
than infants with adequate B6 indices. Despite similar
genetic variability and other dietary factors (163).
protein status at 4, 6 and 9 months determined by plasma
Pronounced calcium deficiency resulting in tetany rarely
total proteins, prealbumin and transferrin, all 7 infants
occurs in the healthy, breastfed infant and therefore is
with low B6 indices presented declines in length-for-
not helpful in determining requirements. Assessment
age Z-scores.
of calcium status is difficult since serum levels are
homeostatically regulated and therefore do not reflect
Kang-Yoon et al. (160) evaluated the growth of infants
body content. Inadequate calcium intake can result in
of well-nourished women supplemented with 2 or 27
lower-than-normal bone mineralization. Single-beam
mg PL-HCl/day during the first month postpartum. A
X-ray densitometry and, more recently, dual-energy X-
subgroup was selected from infants born to women who
ray absorptiometry (DXA) have been used to measure
received a 2 mg vitamin B6 supplement. This subgroup
bone mineral content (BMC) and BMD.
of infants was supplemented postnatally with 0.4 mg of
vitamin B6. This subgroup, and infants whose mothers
Using DXA, breastfed infants have been shown to
were supplemented at the higher level, achieved higher
have lower BMC and BMD than formula-fed infants
weight-for-age and length-for-age Z-scores than infants
at 6 months (164) and 12 months (37). However,
of women supplemented at the lowest level despite
the clinical relevance of this is uncertain since the
similar values at entry.
differences in bone mineralization did not persist beyond
weaning (37, 164). Since bone mineralization did not
differ between breastfed and formula-fed infants after
3.5.7 Summary
weaning, retention of more calcium than that achieved
by breastfed infants does not seem to benefit bone
Maternal B6 status and intake, length of gestation, stage
mineralization later in life.
of lactation and use of B6 supplements affect the B6
content of human milk. In well-nourished populations,
Compared to British children, BMC at the radius in
human milk appears to maintain normal vitamin B6
Gambian infants was slightly lower at birth, and it fell
status in most exclusively breastfed infants during the
progressively during early childhood such that by 36
first 4 to 6 months of age; the risk of B6 inadequacy
months it was 31% lower (165). The difference
appears to increase beyond 6 months. After 6 months
remained significant after correction for body weight,
of exclusive breastfeeding, low vitamin B6 status in a
height and bone width. Although the BMC of Gambian
mother was associated with low vitamin B6 status in
and British women is remarkably similar, it could be
32

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
argued that the BMC of Gambian women is less than
(140 mg/day) (169) and metacarpal morphometry
their genetic potential, as African Americans are known
(80 mg/day) (170, 171).
to have significantly higher BMC than their fairer-
The calcium requirements of breastfed infants have been
skinned counterparts. Weaning breastfed infants onto
estimated from urinary calcium losses (3 mg/kg per day),
low-calcium diets may compromise later bone
faecal endogenous losses (3 mg/kg per day) (168), and
mineralization.
rates of calcium accretion (Table 10). We estimated
Balance studies in breastfed term infants indicate rates
calcium accretion from BMC measurements by DXA
of absorption ranging from 40 to 70% (166, 167). In
taken at 15 days and 12 months of age (172) on the
breastfed infants, a mean calcium intake was 327 mg/
assumption that 32.2% of BMC was calcium (173).
day and the retention was 80 mg/day (166). Losses
These estimated requirements were based on a small
amounted to 247 mg/day.
number of infants and several assumptions and thus
should be confirmed by further study. Based on the
Stable-isotope studies using 44calcium and 46calcium
estimated calcium intakes of exclusively breastfed
have been used to determine calcium absorption and
infants, the efficiency of calcium absorption would have
retention in term infants (168). Calcium absorption
to be greater than 70% to cover these estimated
measured using stable isotopes averaged 61 ± 23%
requirements.
(range 27–89%) in a study of 14 human milk-fed infants,
aged 5 to 7 months, with a mean weight of 7.8 kg (168).
Based on an assumed milk concentration of 0.25 mg/ml
3.6.3 Summary
and 766 ml/day, an endogenous faecal excretion of 3
Calcium requirements during infancy were derived from
mg/kg per day and a urinary excretion of 3 mg/kg per
stable isotope studies of calcium absorption and
day, these authors estimated from their observations that
retention, and calcium accretion rates. Calcium content
68 mg/day of calcium were retained from human milk
of human milk is fairly constant throughout lactation
(168).
and is not influenced by maternal diet. Based on the
The accretion of body calcium during the first year of
estimated calcium intakes of exclusively breastfed
life has been estimated from changes in body weight
infants, human milk meets the calcium requirements
Table 10. Calcium requirements of breastfed infants
Total
Total
Total
Calcium
Calcium
requirement
requirement
requirement
Calcium
Calcium
endogenous
endogenous
for net
for net
for net
urinary
urinary
faecal
faecal
Calcium
Calcium
Calcium
calcium
calcium
calcium
losses
losses
losses
losses
gain
gain
gain
absorption
absorption
absorption
Age
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(months)
BOYSA
GIRLSA
BOYSB
GIRLSB
BOYSC
GIRLSC
ALL
BOYS
GIRLS
ALL
1
14
13
14
13
131
109
120
158
135
147
2
17
15
17
15
131
109
120
164
140
152
3
19
17
19
17
131
109
120
169
144
156
4
21
19
21
19
131
109
120
173
147
160
5
22
21
22
21
131
109
120
176
151
163
6
24
22
24
22
131
109
120
179
153
166
7
25
23
25
23
131
109
120
181
155
168
8
26
24
26
24
131
109
120
183
157
170
9
27
25
27
25
131
109
120
184
159
172
10
27
26
27
26
131
109
120
186
160
173
11
28
26
28
26
131
109
120
187
161
174
12
29
27
29
27
131
109
120
189
163
176
a Calcium urinary losses (3 mg/kg per day) (168).
b Calcium endogenous faecal losses (3 mg/kg per day) (168).
c Calcium gain (172).
33

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
of infants during the first 6 months of life if the efficiency
ferrin receptor and mean corpuscular volume can be
of absorption is maintained at ~70%, which is within
used to assess iron deficiency.
reported rates (166, 167).
Total body iron is relatively stable from birth to ~4
months of age, but the proportion of body iron in
3.7 Iron
distinct compartments (e.g. red blood cells, myoglobin
and stores) shifts dramatically as stores are depleted and
3.7.1 Human milk composition
demands for iron increase to meet needs imposed from
4 to 12 months of age by expanding red blood cell and
The concentration of iron in human milk declines from
myoglobin compartments. Iron requirements thus rise
~0.4–0.8 mg/l in colostrum to ~0.2–0.4 mg/l in mature
markedly around 4 to 6 months of age (176). These
human milk (33). The iron content of human milk
requirements are very high relative to infants’ energy
appears to be homeostatically controlled by up- and
requirements at this age. Factorial, balance and stable
down-regulation of transferrin receptors in the mam-
isotope methods have been used to estimate infants’ iron
mary gland (174); consequently, it is unaffected by
requirements. Iron needed to recover endogenous losses
maternal iron status or diet.
through the gastrointestinal tract (62 mg/year) and skin
(29 mg/year) has been estimated to be approximately
3.7.2 Estimates of iron requirements
91 mg/year. Iron at 1 year of life as haemoglobin
(270 mg), myoglobin and enzymes (54 mg), and storage
Major factors determining iron requirements during
(53 mg) amounts to 109 mg above the amount present
infancy are iron endowment at birth, requirements for
at birth (268 mg) (177). Using this factorial approach,
growth and a need to replace losses. The newborn infant
the total iron requirement during infancy is ~200 mg/
is well endowed with iron stores and a high concen-
year or 0.55 mg/day. Since there is a substantial increase
tration of haemoglobin. In the first 6 to 8 weeks of life,
in erythrocyte mass and myoglobin between 4 and 12
there is a marked decline in haemoglobin from the
months (176, 178), the iron requirement is thought to
highest to the lowest observed during development due
be higher in later than early infancy. Iron requirements
to the abrupt decrease in erythropoiesis in response to
are thus estimated to be 0.5 mg/day for infants from 0
increased postnatal delivery of oxygen to tissues (175).
to 6 months of age and 0.9 mg/day for infants 6 to 12
In the next stage, between 2 and 4 months of age,
months of age (Table 11).
haemoglobin concentration gradually increases. Eryth-
ropoiesis becomes more active, and there is an increase
in erythroid precursors in the bone marrow and an
Table 11. Iron Requirements of breastfed infants
elevation of the reticulocyte count. Between 4 and 6
months of age, there is an increased dependence on
Faecal
Iron
Total
dietary iron. Dietary iron provides ~30% of the require-
and skin
gain
iron
Age
losses
(mg/day)
requirement
ment for haemoglobin iron turnover, compared to 5%
(months)
(mg/day)
All
(mg/day)
in adults (175). Because of the considerable iron
requirement for growth and the marginal supply of iron
1–6
0.24
0.25
0.49
in infant diets, iron deficiency is prevalent among
7–12
0.37
0.53
0.90
infants between 6 and 12 months of age.
Source: reference 177.
Iron-containing compounds in the body serve metabolic
or enzymatic functions or are used for storage.
Haemoglobin, myoglobin, the cytochromes and several
Iron intakes from human milk are summarized in Table
other proteins function in transport, storage and
4. At a fractional iron absorption rate of 0.20, it is clear
utilization of oxygen. Iron is stored primarily as ferritin
that breastfed infants subsidize their requirements from
and haemosiderin. Iron is mobilized from these reserves
iron reserves in the body. Stable isotope studies using
to maintain haemoglobin and other iron-containing
59Fe have tended to overestimate the absorption of iron
compounds. Body function is unlikely to be impaired
from human milk because of unequal distribution of the
as long as iron reserves are available. When iron reserves
extrinsic label with intrinsic iron in human milk. Recent
are depleted, iron deficiency will result in anaemia.
studies have indicated that the absorption of iron from
Haemoglobin can be used to diagnose iron deficiency
human milk is more likely to be lower – ~19–20% (179,
anaemia although the cut-off value for infants is
180). A balance study in exclusively breastfed term
debated. Serum ferritin, transferrin saturation, trans-
infants resulted in positive iron balances up to 4 months
34

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
of age (181). Recent results using 59Fe and 58Fe indicated
at 3 months postpartum, and to ~0.5 mg/l at 6 months
a median absorption of iron from human milk of 14%
(33). There is considerable inter-individual variation
at 6 months of age, 49% in non Fe-supplemented infants
in milk zinc concentrations; in one study the coefficient
and 18% in Fe-supplemented infants at 9 months of
of variation was 0.25 at 2 weeks postpartum and > 0.50
age. Although iron absorption was enhanced, the iron
at 5 to 7 months (188). Interestingly, milk zinc concen-
in human milk would not be sufficient to meet estimated
tration displays channelling or tracking in individuals
iron requirements (Abrams, personal communication).
throughout lactation. A significant correlation (r=0.60)
was detected between the concentration of zinc in early
Iron status – assessed by the determination of haemo-
milk at 2 weeks postpartum and mature milk at 5 to
globin, red blood cell counts, transferrin, transferrin
7 months (188).
saturation, serum iron and ferritin – of exclusively
breastfed infants was satisfactory up to 6 months of age
Maternal dietary zinc has not been shown to affect the
in studies by Duncan et al. (182), Lönnerdal & Hernell
zinc content of human milk, while concentrations in
(183), Saarinen & Siimes (184) and Simes et al. (185).
human milk seem resistant to zinc supplementation.
Iron status was adequate in one study up to 9 to 12
Studies of lactating women receiving daily zinc supple-
months of age in exclusively breastfed infants (186).
ments did not show any effect on milk zinc concen-
However, other studies demonstrated that breastfed
tration (188, 189), nor did daily doses of 50–150 mg
infants who do not receive iron supplements are at risk
zinc prevent a decline in milk zinc concentration (190).
of becoming iron-deficient in the second half of infancy
A slower rate of decline, however, was observed in
(187, 185).
lactating women supplemented with 15 mg/day zinc for
9 months of lactation (191). A randomized, controlled
supplementation trial by the same group of investigators
3.7.3 Summary
failed to confirm their earlier observations (188). A
Human milk is a poor source of iron and cannot be
supplement of 20 mg/day for 9 months did not increase
altered by maternal iron supplementation. It is clear
mean serum or milk zinc in Finnish women (191).
that the estimated iron requirements of infants cannot
However, a 40-mg supplement increased maternal serum
be met by human milk alone at any stage of infancy.
levels at 2 months and the milk level after 6 months of
The iron endowment at birth adequately provides for
supplementation. A recent study in lactating Spanish
the iron needs of the breastfed infant in the first half of
women provided evidence that both dietary zinc intake
infancy. The iron available for growth and development
and serum zinc concentrations were positively correlated
should be adequate until iron stores are exhausted.
with milk zinc concentrations (193). Women with low
zinc intake in their third trimester of pregnancy (< 10
Factorial and balance methods have been used to
mg/day zinc) had lower concentrations of zinc in their
estimate the iron requirements of infants. Iron require-
milk. A comparison of milk zinc concentrations from
ments are estimated to be 0.5 mg/day for infants from 0
lactating women in developing and developed countries
to 6 months of age and 0.9 mg/day for infants 7 to 12
supports the hypothesis that chronically low dietary zinc
months of age. Human milk’s iron content, which
is associated with lower milk zinc concentrations (194).
declines from ~0.4–0.8 mg/l in colostrum to ~0.2–0.4
mg/l in mature milk, is unaffected by maternal iron status
or diet. The estimated iron intakes of exclusively
3.8.2 Estimates of zinc requirements
breastfed infants are insufficient to meet their iron
Severe zinc deficiency results in acrodermatitis entero-
requirements. At a fractional iron absorption rate of
pathica, impaired immune function, diarrhoea and
0.20, it is clear that breastfed infants subsidize their
growth retardation. Zinc status is commonly assessed
requirements from iron body reserves. It appears that
by serum zinc; however, this indicator is affected by
breastfed infants who do not receive additional iron
other factors, notably infection, stress and growth rate.
from supplements or complementary foods are at risk of
Serum zinc is informative for groups of healthy infants
becoming iron-deficient in the second half of infancy.
but not for assessing individuals.
There are several case reports of severe zinc deficiency
3.8 Zinc
in breastfed term infants receiving milk having lower-
than-normal concentrations of zinc (195–200). Since
3.8.1 Human milk composition
maternal zinc supplementation failed to increase milk
The concentration of zinc in human milk declines
concentrations, zinc uptake or secretion by the mam-
precipitously from 4–5 mg/l in early milk, to 1–2 mg/l
mary gland appeared defective in these cases.
35

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
Mean serum zinc was stable in breastfed infants from 2
In the latter study, the infants all achieved positive zinc
to 9 months, but the number of infants in the low range
balance through relatively high fractional zinc absorp-
(0.55mg/l) increased from 3% at birth to 30% at
tion and conservation of endogenous zinc losses.
between 4 to 9 months (192). Serum zinc correlated
Since there is no pharmacological effect of zinc on
with zinc intake and milk zinc concentrations. However,
growth, zinc supplementation trials of breastfed infants
neither low zinc intakes nor low serum zinc levels were
provide evidence as to whether zinc is limiting growth.
associated with poor growth.
A 3-month intervention trial was undertaken in 4- to
In contrast, a decline in serum zinc and erythrocyte
9-month-old breastfed infants who received either 5 mg/
metallothionein concentration from 6 to 9 months was
day zinc or a placebo (205). A significant increase in
observed in breastfed Danish infants (201). Serum zinc
weight gain and linear growth was observed in the
at 9 months was positively correlated with weight gain
supplemented infants. Complementary foods and
between 6 and 9 months. Mean serum zinc did not
formula use were not reported. Whether the amount of
change significantly between 2 and 6 months, and then
zinc provided by human milk during the complementary
fell significantly between 6 and 9 months, reaching a
feeding period was insufficient or whether properties of
low mean of 8.4 µmol/l.
food interfered with the absorption of zinc from human
milk is uncertain (205).
Median zinc balance in term predominantly breastfed
infants studied at 17, 35, 57, 85 and 113 days of age has
In another random double-blind study, exclusively
been shown to be positive (0.1 mg/kg per day); however,
breastfed infants were assigned to receive a 5 mg/day
the range of zinc balances was high (202) and 33% of
zinc-supplement or placebo from 2 to 6.5 months of age
the infants were in negative balance. Stable-isotope
(206). Zinc supplementation did not enhance the
studies using 67Zn and 70Zn demonstrated equilibration
growth of exclusively breastfed infants. This suggests
of the extrinsic label with intrinsic milk zinc (203). The
either that zinc intakes and stores in these infants were
mean fractional zinc absorption from human milk was
sufficient to sustain growth or, alternatively, that zinc
0.55 or 0.08 mg/kg per day in 2- to 5-month-old breast-
alone may not be limiting the growth of exclusively
fed infants with some variation with infant age (204).
breastfed infants. Zinc, in combination with other trace
Table 12. Zinc requirements of breastfed infants
Total
Urine
Urine
Urine
Endogenous
Endogenous
Endogenous
requirement
and sweat
and sweat
and sweat
faecal
faecal
faecal
Zinc
Zinc
Zinc
for net
losses
losses
losses
losses
losses
losses
gain
gain
gain
zinc
Age
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
(mg/day)
absorption
(months)
BOYSa
GIRLSa
ALL
BOYSb
GIRLSb
ALL
BOYSc
GIRLSc
ALL
(mg/day)
1
0.092
0.087
0.089
0.229
0.218
0.223
0.704
0.566
0.635
0.947
2
0.110
0.103
0.106
0.275
0.257
0.266
0.599
0.507
0.553
0.925
3
0.126
0.116
0.121
0.314
0.291
0.303
0.461
0.421
0.441
0.864
4
0.139
0.128
0.134
0.347
0.321
0.334
0.375
0.362
0.368
0.836
5
0.150
0.138
0.144
0.374
0.346
0.360
0.322
0.309
0.316
0.820
6
0.159
0.147
0.153
0.397
0.368
0.382
0.257
0.257
0.257
0.791
7
0.166
0.154
0.160
0.415
0.386
0.400
0.230
0.217
0.224
0.784
8
0.172
0.161
0.167
0.431
0.402
0.416
0.211
0.184
0.197
0.780
9
0.178
0.166
0.172
0.444
0.416
0.430
0.178
0.171
0.174
0.776
10
0.183
0.171
0.177
0.456
0.428
0.442
0.158
0.158
0.158
0.777
11
0.187
0.175
0.181
0.469
0.437
0.453
0.158
0.145
0.151
0.785
12
0.192
0.180
0.186
0.481
0.450
0.466
0.158
0.145
0.151
0.803
a Urinary and sweat zinc losses (20 µg/kg per day) (209).
b Endogenous faecal zinc losses (50 µg/kg per day) (204).
c Zinc gain (20 µg/g weight gain) (210, 211).
36

3 . E N E R G Y A N D S P E C I F I C N U T R I E N T S
minerals present in very small amounts in human milk,
Mean zinc intakes from human milk are summarized in
might be limiting the growth of older exclusively
Table 4. At an estimated fractional zinc absorption of
breastfed infants.
0.55 (204), net zinc absorption will fall short of actual
zinc needs. Zinc intakes from human milk are subject
Using stable isotope studies, the estimated mean net
to inter-individual variation in milk zinc concentrations.
zinc absorption, which does not include urinary or
Since milk zinc concentration displays significant
integumental losses, was 0.26 mg/day at 2 months and
tracking (r=0.60) in individuals throughout lactation
0.29 mg/day at 4 to 5 months (207). Even with very
(188), infants whose mothers produce low zinc
efficient absorption and conservation of endogenous
concentrations will be at increased risk of zinc
losses, net zinc absorption did not meet zinc require-
deficiency. Since milk intakes are driven by energy needs
ments at 2 months or 4 to 5 months. Mobilization of
and not by zinc requirements, and since milk energy
hepatic zinc bound to metallothionein may supplement
and zinc concentrations are not correlated, milk zinc
the infant’s needs during the first months of life, but by
intakes will not be determined by infant size or growth
4.4 months hepatic metallothionein levels fall to those
potential.
found in older children (208).
Zinc requirements of infants may be estimated by the
factorial method (209). Urinary and sweat zinc losses
3.8.3 Summary
are estimated to be 20 µg/kg per day (209). Zinc required
The concentration of zinc in human milk declines
for new tissue accretion is estimated to be 20 µg/g weight
precipitously between early and mature milk and is
gain or 30 µg/g lean tissue gain (210, 211). Endogenous
basically unaffected by maternal zinc supplementation.
faecal zinc losses are estimated to be 50 µg/kg per day
There is some evidence that chronically low dietary zinc
(204). Total zinc requirements for net zinc absorption
is associated with lower milk zinc concentrations. Zinc
are summarized in Table 12. These estimated zinc
requirements have been estimated by the factorial
requirements should be considered provisional since
method. At an estimated fractional zinc absorption of
they were based on studies with small sample sizes and
0.55, the net zinc absorption from human milk will fall
extrapolated data. Zinc requirements are higher in boys
short of zinc needs, which appear to be subsidized by
than in girls and are highest in early infancy, at the
prenatal stores.
time of greatest weight gain. As growth velocity slows
in later infancy, the losses in urine and sweat exceed
the amount deposited in tissues.
37

N U T R I E N T A D E Q U A C Y O F E X C L U S I V E B R E A S T F E E D I N G F O R T H E T E R M I N F A N T D U R I N G T H E F I R S T S I X M O N T H S O F L I F E
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47

SELECTED WHO PUBLICATIONS OF RELATED INTEREST
The optimal duration of exclusive breastfeeding.
Breastfeeding counselling – a training course,
A systematic review
1993
http://www.who.int/child-adolescent-health/
Document WHO/CHD/95.2
New_Publications/NUTRITION/WHO_CAH_01_23.pdf
HIV and infant feeding
The optimal duration of exclusive breastfeeding.
• Guidelines for decision-makers
Report of an expert consultation
Document WHO/FRH/NUT/CHD/98.1
http://www.who.int/child-adolescent-health/
New_Publications/NUTRITION/WHO_CAH_01_24.pdf
http://www.unaids.org/unaids/document/mother-to-child/
infantpolicy.pdf
• A guide for health care managers and supervisors
Global strategy for infant and young child feeding
Document WHO/FRH/NUT/CHD/98.2
Fifty-fifth World Health Assembly, May 2002,
http://www.unaids.org/unaids/document/mother-to-child/
document A55/15.
infantguide.pdf
http://www.who.int/gb/EB_WHA/PDF/WHA55/ea5515.pdf
• A review of HIV transmission through breastfeeding
Document WHO/FRH/NUT/CHD/98.3
http://www.unaids.org./highband/document/mother-to-child/
WHO Global Database on Growth and
hivmod3.pdf
Malnutrition
http://www.who.int/nutgrowthdb/
Complementary feeding: family foods for
breastfed children
Infant feeding: the physiological basis
2000, iii + 52 pages
1990, 108 pages, ISBN 92 4 068670 3
WHO/NHD/00.1; WHO/FCH/CAH/00.6
Order no. 0036701
In developing countries: Sw.fr. 7.70. Order no. 1930177
Protecting, promoting and supporting breast-
Complementary feeding of young children in
feeding
developing countries
The special role of maternity services. A joint WHO/
A review of current scientific knowledge
UNICEF statement.
1998, ix + 228 pages, WHO/NUT/98.1
1989, iv + 32 pages, ISBN 92 4 156130 0
Order no. 1930141
Order no. 1150326
Evidence for the ten steps to successful
breastfeeding
1998, vi + 111 pages, WHO/CHD/98.9
Order no. 1930142
Further information on these and other
WHO publications can be obtained from
Hypoglycaemia of the newborn
Marketing and Dissemination
Review of the literature
World Health Organization
1997, ii + 55 pages, WHO/CHD/97.1; WHO/MSM/97.1
1211 Geneva 27, Switzerland
Order no. 1930165
e-mail: publications@who.int
Direct fax: +41 22 791 4857
Promoting breast-feeding in health facilities
Phone: +41 22 791 2476
1996, 391 pages, 154 colour slides, eight training modules in
loose-leaf binder, WHO/NUT/96.3
Order no. 1930100
Links to related Web sites:
http://www.who.int/nut/publications.htm
The baby-friendly hospital initiative
Monitoring and reassessment: tools to sustain progress
http://www.who.int/child-adolescent-health
1999, four sections in a loose-leaf binder with computerized
reporting system, WHO/NHD/99.2

This review, which was prepared as part of the background documentation
for a WHO expert consultation, evaluates the nutrient adequacy of exclusive
breastfeeding for term infants during the first 6 months of life. Nutrient
intakes provided by human milk are compared with infant nutrient
requirements. To avoid circular arguments, biochemical and physiological
methods, independent of human milk, are used to define these requirements.
The review focuses on human-milk nutrients, which may become growth
limiting, and on nutrients for which there is a high prevalence of maternal
dietary deficiency in some parts of the world; it assesses the adequacy of
energy, protein, calcium, iron, zinc, and vitamins A, B6, and D. This task is
confounded by the fact that the physiological needs for vitamins A and D,
iron, zinc – and possibly other nutrients – are met by the combined
availability of nutrients in human milk and endogenous nutrient stores.
In evaluating the nutrient adequacy of exclusive breastfeeding, infant
nutrient requirements are assessed in terms of relevant functional outcomes.
Nutrient adequacy is most commonly evaluated in terms of growth, but
other functional outcomes, e.g. immune response and neurodevelopment,
are also considered to the extent that available data permit.
This review is limited to the nutrient needs of infants. It does not evaluate
functional outcomes that depend on other bioactive factors in human milk,
or behaviours and practices that are inseparable from breastfeeding, nor
does it consider consequences for mothers. In determining the optimal
duration of exclusive breastfeeding in specific contexts, it is important that
functional outcomes, e.g. infant morbidity and mortality, also are taken
into consideration.
For further information please contact:
Department of Nutrition for
Department of Child and Adolescent
Health and Development (NHD)
Health and Development (CAH)
World Health Organization
World Health Organization
20 Avenue Appia
20 Avenue Appia
1211 Geneva 27
1211 Geneva 27
Switzerland
Switzerland
Tel: +41 22 791 3320
Tel +41-22 791 3281
Fax: +41 22 791 4156
Fax +41-22 791 4853
email: deonism@who.int
email: cah@who.int
website: www.who.int/nut
website: http://www.who.int/child-adolescent-health