Low zinc intake during exclusive breast-feeding does not impair growth

Human Milk Micronutrients and Child Growth and Body Composition in the First 2 years: A Systematic Review

Human milk (HM) provides a plethora of nutritional and non-nutritional compounds that support infant development. For many compounds, concentrations vary substantially among mothers and across lactation, and their impact on infant growth is poorly understood. We systematically searched MEDLINE, Embase, the Cochrane Library, Scopus, and Web of Science to synthesize evidence published between 1980 and 2022 on HM components and anthropometry through 2 y of age among term-born infants. Outcomes included weight-for-length, length-for-age, weight-for-age, body mass index (in kg/m2)-for-age, and growth velocity. From 9992 abstracts screened, 144 articles were included and categorized based on their reporting of HM micronutrients, macronutrients, or bioactive components. Micronutrients (vitamins and minerals) are reported here, based on 28 articles involving 2526 mother-infant dyads. Studies varied markedly in their designs, sampling times, geographic and socioeconomic settings, reporting practices, and the HM analytes and infant anthropometrics measured. Meta-analysis was not possible because data were sparse for most micronutrients. The most-studied minerals were zinc (15 articles, 1423 dyads) and calcium (7 articles, 714 dyads). HM iodine, manganese, calcium, and zinc concentrations were positively associated with several outcomes (each in ≥2 studies), whereas magnesium (in a single study) was negatively associated with linear growth during early lactation. However, few studies measured HM intake, adjusted for confounders, provided adequate information about complementary and formula feeding, or adequately described HM collection protocols. Only 4 studies (17%) had high overall quality scores. The biological functions of individual HM micronutrients are likely influenced by other HM components; yet, only 1 study analyzed data from multiple micronutrients simultaneously, and few addressed other HM components. Thus, available evidence on this topic is largely inconclusive and fails to address the complex composition of HM. High-quality research employing chronobiology and systems biology approaches is required to understand how HM components work independently and together to influence infant growth and to identify new avenues for future maternal, newborn, or infant nutritional interventions.

Association of maternal diet, micronutrient status, and milk volume with milk micronutrient concentrations in Indonesian mothers at 2 and 5 months postpartum

BACKGROUND

Maternal micronutrient deficits during preconception and pregnancy may persist during lactation and compromise human milk composition.

OBJECTIVE

We measured micronutrient concentrations in human milk and investigated their association with maternal micronutrient intakes, status, and milk volume.

METHODS

Infant milk intake (measured via a deuterium dose-to-mother technique), milk micronutrient and fat concentrations, and maternal micronutrient intakes were assessed at 2 and 5 mo postpartum in 212 Indonesian lactating mother-infant pairs. Maternal hemoglobin, ferritin, transferrin receptors, retinol binding protein (RBP), zinc, selenium, and vitamin B-12 were measured at 5 mo (n = 163). Multivariate or mixed effects regression examined associations of milk micronutrient concentrations with maternal micronutrient intakes, status, and milk volume.

RESULTS

Prevalence of anemia (15%), and iron (15% based on body iron), selenium (2.5%), and vitamin B-12 deficiency (0%) were low compared with deficiencies of zinc (60%) and vitamin A (34%). The prevalence of inadequate intakes was >50% for 7 micronutrients at 2 and 5 mo. Median milk concentrations for most micronutrients were below reference values, and nearly all declined between 2 and 5 mo postpartum and were not associated substantially with milk volume (except for β-carotene, α-carotene, and β-cryptoxanthin). At 5 mo postpartum, associations between maternal micronutrient status and corresponding milk concentrations reported as mean percentage difference in human milk concentration for each unit higher maternal biomarker were significant for hemoglobin (1.9%), iron biomarkers (ranging from 0.4 to 7%), RBP (35%), selenium (70%), and vitamin B-12 (0.1%), yet for maternal intakes only a positive association with β-carotene existed.

CONCLUSIONS

Most milk micronutrient concentrations declined during lactation, independent of changes in human milk production, and few were associated with maternal micronutrient intakes. The significant associations between maternal biomarkers and milk micronutrient concentrations at 5 mo warrant further study to investigate whether the declines in milk micronutrients are linked to shifts in maternal status.

Nutritional and Non-nutritional Composition of Human Milk Is Modulated by Maternal, Infant, and Methodological Factors

Human milk (HM) is dynamic and shows a high inter- and intra-individual variability. To characterize HM with precision, it is necessary to understand the factors that modulate its composition. The objective of this narrative review is to summarize the maternal, infant and methodological factors that affect HM composition. We searched SCOPUS and PubMed databases for articles related to factors that are known to or could potentially influence HM composition and volume across lactation periods. Our comprehensive review encompasses various maternal-, infant-related, and methodological factors that modulate aspects of HM composition including macro- and micronutrients, vitamins and minerals, as well as volume. The most profound changes were observed in HM lipids and lipophiles. Evidence exists for many of the infant-related factors known to affect the nutritive and non-nutritive components of HM (e.g., birth weight, gestational age, infant age/stage of lactation). In contrast, less is known with respect to maternal factors; where there is either limited research or conflicting evidence (e.g., maternal lifestyle, obstetric history, medical conditions), except for the mother's diet, for which there is a relatively well-established understanding. Equally, although many of the methodological factors (e.g., HM sampling, handling and analytics) are known to impact HM composition, few studies have investigated this as a primary outcome, making it an important area of future research in HM. Here we propose a systematic capture of numerous maternal- and infant-related characteristics to facilitate associative comparisons of HM data within and across studies. Additionally, it would be prudent to standardize the methodological aspects known to affect HM composition in analytics, not only for HM lipids and lipophiles, but also for those nutrients whose variability is yet less well-understood. Defining the factors determining HM composition with accuracy will open perspectives for maternal intervention to optimize milk composition for specific needs of infants.

Constituents of Human Milk

Breastmilk contains all the nutrients required by the newborn baby. It also contains non-nutritional components that may promote infant health, growth, and development, such as antimicrobial factors, digestive enzymes, hormones, trophic factors, and growth modulators. In some situations, breastmilk may also contain harmful components, such as pollutants, drugs, allergens, and viruses. Human milk has a unique composition, which differs from that of other mammals in its ingredients and their concentrations.

Breastmilk composition is not constant and varies with stage of lactation, breastfeeding pattern, season, and parity. It also differs among individuals and among communities, for reasons that are not well understood. Maternal nutrition is an obvious candidate, but the situation is complex. Supplementation studies and cross-cultural comparisons have demonstrated that the total concentrations of fat, protein, and lactose are relatively insensitive to current dietary intake and nutritional status, whereas the fatty acid profile and the concentrations of several micronutrients, particularly water-soluble vitamins, are responsive to maternal diet.

For many infants, nutrient intake from breastmilk becomes insufficient after four to six months, and other foods should be added to the diet. Nevertheless, breastmilk can continue to be a valuable nutrient source and to provide non-nutritional factors even for older children. Consequently, breastfeeding for one to two years as part of a mixed diet has many advantages, particularly for children living in impoverished circumstances.

Modifiable "Predictors" of Zinc Status in Toddlers

Suboptimal zinc status is common in very young children and likely associated with increased risk of infection and detrimental effects on growth. No studies have determined potentially modifiable "predictors" of zinc status in toddlers from high-income countries. This cross-sectional analysis of 115 toddlers from the Baby-Led Introduction to SolidS (BLISS) study used weighed diet records (three non-consecutive days) to assess dietary intake, and a venous blood sample (trace-element free techniques) to assess plasma zinc, at 12 months of age. "Predictors" of plasma zinc were determined by univariate analysis and multiple regression. Mean (SD) plasma zinc was 9.7 (1.5) μmol/L, 60% were below the IZiNCG reference limit of <9.9 μmol/L. Median (25th, 75th percentiles) intake of zinc was 4.4 (3.7, 5.4) mg/day. Red meat intake (p = 0.004), consumption of zinc-fortified infant formula (3-6 mg zinc/100 g) (p = 0.026), and food fussiness (p = 0.028) were statistically significant "predictors" of plasma zinc at 12 months. Although higher intakes of red meat, and consumption of infant formula, are potentially achievable, it is important to consider possible barriers, particularly impact on breastfeeding, cost, and the challenges of behavior modification. Of interest is the association with food fussiness-further research should investigate the direction of this association.

The Effect of Low Dose Iron and Zinc Intake on Child Micronutrient Status and Development during the First 1000 Days of Life: A Systematic Review and Meta-Analysis

Adequate supply of micronutrients during the first 1000 days is essential for normal development and healthy life. We aimed to investigate if interventions administering dietary doses up to the recommended nutrient intake (RNI) of iron and zinc within the window from conception to age 2 years have the potential to influence nutritional status and development of children. To address this objective, a systematic review and meta-analysis of randomized and quasi-randomized fortification, biofortification, and supplementation trials in women (pregnant and lactating) and children (6–23 months) delivering iron or zinc in doses up to the recommended nutrient intake (RNI) levels was conducted. Supplying iron or zinc during pregnancy had no effects on birth outcomes. There were limited or no data on the effects of iron/zinc during pregnancy and lactation on child iron/zinc status, growth, morbidity, and psychomotor and mental development. Delivering up to 15 mg iron/day during infancy increased mean hemoglobin by 4 g/L (p < 0.001) and mean serum ferritin concentration by 17.6 µg/L (p < 0.001) and reduced the risk for anemia by 41% (p < 0.001), iron deficiency by 78% (ID; p < 0.001) and iron deficiency anemia by 80% (IDA; p < 0.001), but had no effect on growth or psychomotor development. Providing up to 10 mg of additional zinc during infancy increased plasma zinc concentration by 2.03 µmol/L (p < 0.001) and reduced the risk of zinc deficiency by 47% (p < 0.001). Further, we observed positive effects on child weight for age z-score (WAZ) (p < 0.05), weight for height z-score (WHZ) (p < 0.05), but not on height for age z-score (HAZ) or the risk for stunting, wasting, and underweight. There are no studies covering the full 1000 days window and the effects of iron and zinc delivered during pregnancy and lactation on child outcomes are ambiguous, but low dose daily iron and zinc use during 6–23 months of age has a positive effect on child iron and zinc status.

Dietary Sources of Zinc and Factors Affecting its Bioavailability

Zinc is one of the more ubiquitous of nutrients, being found in modest amounts in a large number of foods. Human evolution has undoubtedly shaped the needs for zinc to be absorbed from our beverages and foods of both animal and plant origin in the diet. Different environmental and ecological circumstances modify the amount of zinc that needs to become available to individuals of different regions. We use an acronym approach to review and understand the bioavailability of zinc. The biological availability of zinc can be limited by many factors intrinsic and extrinsic to the host, and it can be enhanced by few. Challenges remain in assessing the bioavailability of zinc compounds as fortificants and in developing strategies to improve the uptake of the metal by reducing phytate and tannin content of diets, either through food technology or plant genetics.

Impact of vitamin A with zinc supplementation on malaria morbidity in Ghana

BACKGROUND

Malaria is a leading cause of morbidity and mortality among young children and is estimated to cause at least 1 million deaths each year especially among pregnant women and young children under the age of five years. Vitamin A supplementation is known to reduce morbidity and mortality in young children. Zinc is required for growth and immunity and we sought to replicate the study by Zeba et al. which showed 30% lower cases of clinical malaria in children on a combination of zinc and a large dose of vitamin A compared with children on vitamin A alone based on the hypothesis that combined vitamin A and zinc reduced symptomatic malaria compared to vitamin A alone.

OBJECTIVES

The primary objective was to determine the effect of vitamin A alone vs. vitamin A and zinc supplements on the incidence of clinical malaria and other anthropometric indices. It also sought to assess the effects on the incidence of anaemia, diarrhoea and pneumonia.

METHODS

The study was community-based and 200 children between the ages of 6-24 months were randomised to receive either vitamin A (100,000 IU for infants less than 12 months & 200,000 IU for children greater than 12 months and 10 mg daily zinc in the intervention group or vitamin A and zinc placebo for 6 months in the control group.

RESULTS

The number of children who were diagnosed with uncomplicated malaria in the intervention group was 27% significantly lower compared with the children in the control group (p = 0.03). There were, however, no effects on severe malaria, pneumonia, anaemia and diarrhea.

CONCLUSIONS

Our study confirms a significant role of vitamin A and zinc in reducing malaria morbidity.

Effect of breastfeeding on serum zinc levels and growth in healthy infants

BACKGROUND

This study investigated the association among breastfeeding, serum zinc levels, and nutritional status of children.

SUBJECTS AND METHODS

One hundred healthy infants were included in the study. Anthropometric measurements of the children were taken, and their plasma zinc levels were determined. The mothers were interviewed about the duration of breastfeeding and nutrition pattern of the children at the time of zinc measurement.

RESULTS

Low zinc levels were associated with lower weight measurements (r=0.49, p<0.001), but the association between height and zinc level was not statistically significant (r=0.18, p>0.05). There was a negative correlation between breastfeeding duration and weight-for-age percentile (r=-0.2, p<0.05), height-for-age percentile (r=-0.3, p<0.05), and serum zinc level (r=-0.3, p=0.002). The pattern of nutrition correlated only with the weight of the infant (r=0.2, p<0.05) and not with either height or serum zinc levels (p>0.05).

CONCLUSIONS

Exclusive breastfeeding beyond 6 months of age has negative effects on serum zinc levels and can be associated with low weight gain, which will be especially important in developing countries.

Maternal zinc intakes and homeostatic adjustments during pregnancy and lactation

Zinc plays critical roles during embryogenesis, fetal growth, and milk secretion, which increase the zinc need for pregnancy and lactation. Increased needs can be met by increasing the dietary zinc intake, along with making homeostatic adjustments in zinc utilization. Potential homeostatic adjustments include changes in circulating zinc, increased zinc absorption, decreased zinc losses, and changes in whole body zinc kinetics. Although severe zinc deficiency during pregnancy has devastating effects, systematic reviews and meta-analysis of the effect of maternal zinc supplementation on pregnancy outcomes have consistently shown a limited benefit. We hypothesize, therefore, that zinc homeostatic adjustments during pregnancy and lactation improve zinc utilization sufficiently to provide the increased zinc needs in these stages and, therefore, mitigate immediate detrimental effects due to a low zinc intake. The specific questions addressed are the following: How is zinc utilization altered during pregnancy and lactation? Are those homeostatic adjustments influenced by maternal zinc status, dietary zinc, or zinc supplementation? These questions are addressed by critically reviewing results from published human studies on zinc homeostasis during pregnancy and lactation carried out in different populations worldwide.

Prenatal zinc supplementation of zinc-adequate rats adversely affects immunity in offspring

We previously showed that zinc (Zn) supplementation of Zn-adequate dams induced immunosuppressive effects that persist in the offspring after weaning. We investigated whether the immunosuppressive effects were due to in utero exposure and/or mediated via milk using a cross-fostering design. Pregnant rats with adequate Zn nutriture were supplemented with either Zn (1.5 mg Zn in 10% sucrose) or placebo (10% sucrose) during pregnancy (3 times/wk). At postnatal d 3, 4 pups of Zn-supplemented dams (Zn-P) were exchanged with 4 of placebo-supplemented dams (P-Zn). The remaining pups continued with their biological mothers (Zn-Zn and P-P). Pups were orally immunized with dinitrophenol ovalbumin-BSA and/or cholera toxin B subunit (CTB), and serum Zn concentrations and cellular and humoral responses were assessed. Pups of Zn-supplemented dams had higher serum Zn when fostered either by placebo- or Zn-supplemented dams compared to pups of placebo-supplemented dams (P < 0.01). Postnatal Zn exposure reduced the number of Peyer's patches in both the Zn-Zn and P-Zn groups (P < 0.01). Prenatal Zn exposure suppressed CTB- (P = 0.05) and BSA-specific proliferation response of Peyer's Patch lymphocytes (P = 0.07). Prenatal Zn exposure effects on the splenocyte cytokine response were differently influenced by fostering mothers' Zn status. Antigen presenting cell (APC) activity of splenocytes was lower in the Zn-Zn group than in the P-P group (P < 0.08). In conclusion, prenatal Zn exposure increases serum Zn levels in pups and suppresses antigen-specific proliferation and antibody responses and APC function, whereas postnatal exposure may suppress the mucosal immune reservoir.

Zinc and copper concentrations in human preterm milk

Zinc and copper are important trace elements in the nutrition of preterm infants. This study determined and compared the concentrations of zinc and copper in preterm milk of mothers receiving and not receiving zinc supplementation diets. The effects of maternal supplementation on the blood levels and anthropometric parameters were evaluated. Thirty-eight mothers and their preterm infants were enrolled in the study. Eighteen mothers were given a daily supplementation of 50 mg zinc, whereas the other 20 were not. Zinc and copper levels in milk were determined at 15-day intervals, as were blood zinc levels along with anthropometric parameters. Zinc and copper contents were determined by atomic absorption spectrophotometry. No significant differences were found between groups either for zinc values in maternal milk and infant blood or for anthropometric measurements. A pronounced decrease in copper levels was observed in mothers receiving supplemental zinc. Zinc supplementation given to mothers who were breastfeeding preterm infants had no significant effect on zinc secretion in milk.

Effects of maternal zinc supplementation on pregnancy and lactation outcomes

Observational studies in human populations suggest that maternal zinc deficiency during pregnancy may cause adverse pregnancy outcomes for the mother and fetus. Therefore, we reviewed the current evidence from studies of zinc supplementation, with or without other micronutrients, during pregnancy and lactation to assess its impact on maternal, fetal, and infant health. A meta-analysis of supplementation trials indicates a 14% reduction in premature delivery among zinc-supplemented women. Most studies found no significant impact of maternal zinc supplementation on infant birthweight, but a subset of studies conducted in underweight or zinc-deficient women suggests that there may be a positive effect of zinc supplementation in such women. However, the number of relevant studies is limited, and more information is needed to confirm these observations. The results for other pregnancy outcomes are inconsistent, and the number of available studies is small. Likewise, the impact of maternal zinc supplementation during pregnancy on infant postnatal growth and risk of infection is variable, and few studies are available. Thus, more research will be needed to allow definitive conclusions to be drawn, especially for the second half of infancy and later childhood. Studies found no adverse effects of maternal zinc supplementation on iron status during pregnancy. More information is required on other potential adverse effects, particularly with regard to a possible modifying effect of preexisting maternal zinc status. In view of the possible benefits of zinc supplementation for reducing the risk of premature delivery, the possible positive impact of zinc supplementation on infant birthweight among undernourished women, and the lack of reported adverse effects, zinc should be included in maternal supplements given during pregnancy in populations at risk for zinc deficiency.

Dietary intervention strategies to enhance zinc nutrition: promotion and support of breastfeeding for infants and young children

Breastmilk is the only dietary source of zinc for exclusively breastfed young infants, and it remains a potentially important source of zinc for older infants and young children who continue breastfeeding beyond early infancy. Therefore, we examined available information on breastmilk zinc concentration and total milk consumption to develop estimates of the amount of zinc transferred in breastmilk to children of different ages. Breastmilk zinc concentration declines rapidly during the first few months postpartum and more slowly thereafter. Breastmilk supplies all of the theoretical zinc needs for at least the first several months of life, although the period during which breastmilk alone remains sufficient is uncertain. Breastmilk continues to provide more than half of children's estimated zinc requirements after the introduction of complementary foods, even into the second year of life. Public health programs to promote and support breastfeeding should be included among the strategies to ensure adequate zinc status of young children.

Exclusive breast-feeding for 6 months, with iron supplementation, maintains adequate micronutrient status among term, low-birthweight, breast-fed infants in Honduras

There is little information on the risk of micronutrient deficiencies during the period of exclusive breast-feeding. We evaluated this among term, low-birthweight (LBW; 1500-2500 g) infants in Honduras. Mother-infant pairs were recruited in the hospital and assisted with exclusive breast-feeding during the first 4 mo. At 4 mo, infants were randomly assigned to either continue exclusive breast-feeding to 6 mo (EBF; n = 59) or be given iron-fortified complementary foods (rice, chicken, fruits, and vegetables) from 4 to 6 mo while continuing to breast-feed (SF, n = 60). Blood samples were collected at 2, 4, and 6 mo and analyzed for hemoglobin (Hb), hematocrit, plasma ferritin, % transferrin saturation, vitamin A, vitamin B-12, folate, zinc, and erythrocyte folate. Infants with Hb < 100 g/L at 2 or 4 mo were given medicinal iron supplements for 2 mo; the proportion administered iron drops did not differ significantly between groups. There was no significant effect of complementary foods on indices of vitamin A, B-12, folate, or zinc status. Among infants not given medicinal iron at 4-6 mo, iron status was higher in the SF group than the EBF group. In those given medicinal iron at 4-6 mo, iron status was higher in the EBF group, suggesting that complementary foods interfered with iron utilization. About half of the infants were anemic by 2 mo, before the age when complementary foods would be recommended. This supports the recommendation that LBW infants should receive iron supplementation in early infancy. Given that infants given iron supplements did not benefit from complementary foods at 4-6 mo, we conclude that exclusive breast-feeding for 6 mo (with iron supplementation) can be recommended for term, LBW infants.

Zinc and breastfed infants: if and when is there a risk of deficiency?

Infancy is a time of relatively high zinc requirements. Human milk provides an excellent source of highly bioavailable zinc and generally meets the needs of the healthy young exclusively breastfed infants for the first several months of life. Investigations of exclusively breastfed infants less than 6 mo of age have generally found zinc homeostasis and status to be adequate, although there are indications that zinc intake from human milk alone may become limiting by around 6 mo of age. Exceptions may be small for gestational age and low birth weight infants, who may well benefit from increased zinc intake before 6 mo of age. The older infant clearly becomes dependent on non-human milk sources of zinc, i.e., from complementary foods. Traditional early complementary foods, such as cereals, fruits, and vegetables provide very modest amounts of zinc, and for those high in phytic acid, bioavailability may be low. Introduction of animal products or zinc supplementation may be important to meet the older infant's zinc requirements This is likely to be particularly important in less protected environments with a high infectious burden and limited dietary options.

Zinc transfer to the breastfed infant

Zinc is a micronutrient which is critical to normal growth and development. Zinc concentrations in human milk decline sharply during the early months post partum, regardless of maternal zinc intake. Milk zinc concentrations do not increase in response to increased maternal zinc intake if maternal zinc status is adequate. The mechanism of zinc secretion into milk is not fully understood. A mutation in the gene for a zinc transporter protein may account for abnormally low milk zinc concentrations associated with severe zinc deficiency in breastfed infants. The zinc requirements of breastfed infants are generally met with exclusive breastfeeding through 5-6 months of age, due to the favorable bioavailability of the zinc in human milk. Because of declining milk zinc concentrations and intake, zinc status in exclusively breastfed infants is likely to become marginal beyond 6 months of age, and may become suboptimal for some infants if exclusive breastfeeding continues. The choice of complementary foods is important to maintain adequate zinc status in breastfed infants after 6 months.

Long-term effects of iron:zinc interactions on growth in rats

The influence of iron (Fe) on the bioavailability and functional status of zinc (Zn) was studied in young rats using metabolic balances and tissue dosages, which were compared to growth. Diets supplied adequate intakes of Fe (45 and 300 mg/kg diet) and Zn (14 and 45 mg/kg) for 2 mo. Two metabolic balance determinations were performed that were correlated for Zn and Fe during the first and the last weeks of the study. A significant effect of Fe supply, but not of Zn was displayed on Fe absorption; both Fe and Zn diet concentrations had a significant influence on Zn absorption. Fe and Zn organ contents were significantly correlated with the amount absorbed during the two metabolic balances. There was a positive correlation between liver and muscle Fe and Fe absorption, and Fe absorption and muscle Zn, as well as a negative one with liver Zn; a positive correlation was displayed between Zn absorption and Zn organ content. No correlation was found between Zn absorption and Fe tissue content. Growth was correlated with Zn, but not with Fe absorption during both balances. A positive correlation was displayed between growth and Zn liver content, and a negative one with Fe liver content. Care must be taken to give growing subjects balanced diets or supplementation, since the negative interactions between these trace elements are likely to persist as long as the diet is given.

The growth and nutritional status of the breast-fed infant

The literature on the relationship between early infant feeding and growth shows that after the first 3 or 4 months, breast-fed infants in the developed world are lighter than formula-fed infants with markedly lower adiposity. There is some evidence of a slightly lower rate of linear growth over the first year or so. These differences in weight and length do not apparently persist beyond the first few years of life. In the developing world the situation is very different. The growth curves of breast-fed infants of malnourished mothers may falter between the third and sixth month of life. However, the generally poor quality of the supplementary foods offered in the developing world and the increased risk of diarrhoeal infections mean that supplementary feeding before the age of 6 months is unlikely to lead to a growth advantage and may well lead to growth faltering.

Properties of human milk and their relationship with maternal nutrition

The composition of human milk varies over the course of lactation and in each individual. The volume of breast milk produced is related to the weight of the infant. Human milk is markedly different from cows' milk, both in terms of macronutrients and micronutrients. This includes the types of fatty acids present and factors affecting their absorption. The types of proteins present and their relative proportions and both qualitative and quantitative differences in the non-protein nitrogen fraction. There is much less lactose in cows' milk than breast milk and the oligosaccharide fraction is very different. Their are major differences in content and absorption rates of vitamins and minerals from breast milk compared to cows' milk or formula milk. Vitamin D and vitamin K status are possible problems for the breast-fed infant in certain circumstances. The nutritional status of the mother appears to influence fat concentration and thus the energy content of breast milk as well as its fatty acid composition and immunological properties. There is no coherent evidence, however, that the protein or lactose concentrations are greatly affected. There is some evidence that the concentration of vitamins in the breast milk are influenced by the mother's intake. Minerals are less variable, with the exception of selenium. The response of the infant to human and formula milk differs with respect to endocrine function, stool motility, immune function and renal function. Infant formula milks are designed to mimic human milk as much as possible, but this is unlikely to ever be completely successful. A number of important compositional differences between human milk and formula milk remain. This includes the types and proportions of fatty acids present (which may be of developmental importance), the nature of the non-protein nitrogen component (also possible developmental importance) and the presence of immunoglobulins and fibronectin (which may protect the infant against infection).

Detecting subclinical deficiency of essential trace elements in children with special reference to zinc and selenium

OBJECTIVE

This article reviews situations in which we should be alert to the risk of trace element deficiencies, and the difficulties of assessing trace element status, as illustrated by states of potential subclinical deficiency of zinc and selenium in infants.

CONCLUSION

Deficiency states of many trace elements have been documented in infants, and there is probably an underdiagnosed group of infants with subclinical deficiency, from which however the great majority are protected by effective regulatory systems. Specific, sensitive, and reliable methods are needed for the detection of trace element imbalances.