The effects of a dietary zinc supplement during lactation on longitudinal changes in maternal zinc status and milk zinc concentrations

Zinc for GNAO1 encephalopathy: Preclinical profiling and a clinical case

BACKGROUND

De novo pathogenic variants in GNAO1-the gene encoding the major neuronal G protein Gαo-cause pediatric encephalopathies and other neurological deficiencies largely refractory to available therapies. Zn2+ emerged to restore guanosine triphosphate hydrolysis and cellular interactions of pathogenic Gαo; dietary zinc salt supplementation improves lifespan and motoric function in a Drosophila disease model.

METHODS

Using biochemical, animal, and first-in-human studies, we provide support for the patient stratification and application of zinc acetate in GNAO1-associated disorders.

FINDINGS

We show that 16 different pathogenic missense variants cluster in three distinct groups in their responsiveness to Zn2+, and we provide the safety study in a mouse disease model. We further describe treatment of a 3-year-old patient with the common pathogenic GNAO1 variant c607G>A, p.Gly203Arg with oral 50 mg zinc (in the form of zinc acetate) daily, as applied in Wilson's disease. During 11 months of treatment, the patient shows cessation of daily dyskinetic crises, improved Burke-Fahn Marsden Dystonia Rating Scale movement score, reduction in epileptic seizures, and an excellent safety profile.

CONCLUSIONS

Our findings warrant a large-scale clinical trial and might set the new standard of care for GNAO1-related disorders.

FUNDING

This work was funded by the Russian Science Foundation (grant #21-15-00138) and GNAO1 España.

Nutritional Status of Breastfeeding Mothers and Impact of Diet and Dietary Supplementation: A Narrative Review

Adequate nutrition during breastfeeding is crucial for ensuring the good health of mothers and babies. Despite the high energy and nutrient demands of breastfeeding, lactating women are often vulnerable from a nutritional perspective. The nutritional focus during breastfeeding tends to be on the newborn, often neglecting the mother's diet. Therefore, in the present narrative review, nutrient intakes were compared with the dietary reference values (DRVs) proposed by the European Food Safety Authority (EFSA) as well as by the World Health Organization/Food and Agriculture Organization (WHO/FAO). In the diets of lactating mothers, dietary inadequacies were observed in the intake of some vitamins, such as folic acid, vitamin B12, vitamin A, and vitamin D, and in the intake of certain minerals like calcium, iron, and iodine; polyunsaturated omega-3 fatty acid deficiencies, primarily in eicosapentaenoic acid and docosahexaenoic acid, were also observed. On the other hand, the debate on the necessity of supplementation during lactation continues; the need for nutritional supplementation during lactation depends on many factors, such us mothers' eating habits. There seems to be a positive association between nutritional supplementation of the lactating mother and the concentration of certain nutrients in human milk. The present narrative review provides an update on the nutritional status (fatty acids and micronutrients) of breastfeeding mothers and the impact of diet and dietary supplementation on human milk composition.

Unraveling the versatility of human serum albumin - A comprehensive review of its biological significance and therapeutic potential

Human serum albumin (HSA) is a multi-domain macromolecule with diverse ligand binding capability because of its ability to allow allosteric modulation despite being a monomeric protein. Physiologically, HSA act as the primary carrier for various exogenous and endogenous compounds and fatty acids, and alter the pharmacokinetic properties of several drugs. It has antioxidant properties and is utilized therapeutically to improve the drug delivery of pharmacological agents for the treatment of several disorders. The flexibility of albumin in holding various types of drugs coupled with a variety of modifications makes this protein a versatile drug carrier with incalculable potential in therapeutics. This review provides a brief outline of the different structural properties of HSA, and its various binding sites, moreover, an overview of the genetic, biomedical, and allosteric modulation of drugs and drug delivery aspects of HSA is also included, which may be helpful in guiding advanced clinical applications and further research on the therapeutic potential of this extraordinary protein.

Nutritional supplements and mother's milk composition: a systematic review of interventional studies

BACKGROUND

This study aims to systematically review the effects of maternal vitamin and/or mineral supplementation on the content of breast milk.

METHODS

We systematically searched electronic databases including Medline via PubMed, Scopus and ISI Web of Science till May 24, 2018. The following terms were used systematically in all mentioned databases: ("human milk" OR "breast milk" OR "breast milk composition" OR "human breast milk composition" OR "composition breast milk" OR "mother milk" OR "human breast milk" OR "maternal milk") AND ("vitamin a" OR "retinol" OR "retinal" OR "retinoic acid" OR "beta-carotene" OR "beta carotene" OR "ascorbic acid" OR "l-ascorbic acid" OR "l ascorbic acid" OR "vitamin c" OR "vitamin d" OR "cholecalciferol" OR "ergocalciferol" OR "calciferol" OR "vitamin e" OR "tocopherol" OR "tocotrienol" OR "alpha-tocopherol" OR "alpha tocopherol" OR "α-tocopherol" OR "α tocopherol" OR "vitamin k" OR "vitamin b" OR "vitamin b complex" OR "zinc" OR "iron" OR "copper" Or "selenium" OR "manganese" OR "magnesium") and we searched Medline via Medical subject Headings (MeSH) terms. We searched Google Scholar for to increase the sensitivity of our search. The search was conducted on human studies, but it was not limited to the title and abstract. Methodological quality and risk of bias of included studies were evaluated by Jadad scale and Cochrane risk of bias tools, respectively.

RESULTS

This review included papers on three minerals (zinc, iron, selenium) and 6 vitamins (vitamin A, B, D, C, E and K) in addition to multi-vitamin supplements. Although studies had different designs, e.g. not using random allocation and/or blinding, our findings suggest that maternal use of some dietary supplements, including vitamin A, D, vitamin B1, B2 and vitamin C might be reflected in human milk. Vitamin supplements had agreater effect on breast milk composition compared to minerals. Higher doses of supplements showed higher effects and they were reflected more in colostrum than in the mature milk.

CONCLUSION

Maternal dietary vitamin and/or mineral supplementation, particularly fat- soluble vitamins, vitamin B1, B2 and C might be reflected in the breast milk composition. No difference was found between mega dose and single dose administration of minerals.

Human Milk Composition and Dietary Intakes of Breastfeeding Women of Different Ethnicity from the Manawatu-Wanganui Region of New Zealand

Human milk is nutrient rich, complex in its composition, and is key to a baby’s health through its role in nutrition, gastrointestinal tract and immune development. Seventy-eight mothers (19–42 years of age) of Asian, Māori, Pacific Island, or of European ethnicity living in Manawatu-Wanganui, New Zealand (NZ) completed the study. The women provided three breast milk samples over a one-week period (6–8 weeks postpartum), completed a three-day food diary and provided information regarding their pregnancy and lactation experiences. The breast milk samples were analyzed for protein, fat, fatty acid profile, ash, selected minerals (calcium, magnesium, selenium, zinc), and carbohydrates. Breast milk nutrient profiles showed no significant differences between the mothers of different ethnicities in their macronutrient (protein, fat, carbohydrate, and moisture) content. The breast milk of Asian mothers contained significantly higher levels of polyunsaturated fatty acids (PUFAs), omega-3 (n-3) and omega-6 (n-6) fatty acids, docosahexaenoic acid (DHA), and linoleic acids. Arachidonic acid was significantly lower in the breast milk of Māori and Pacific Island women. Dietary intakes of protein, total energy, saturated and polyunsaturated fat, calcium, phosphorus, zinc, iodine, vitamin A equivalents, and folate differed between the ethnic groups, as well as the number of serves of dairy foods, chicken, and legumes. No strong correlations between dietary nutrients and breast milk components were found.

The effects of a lipid-based nutrient supplement and antiretroviral therapy in a randomized controlled trial on iron, copper, and zinc in milk from HIV-infected Malawian mothers and associations with maternal and infant biomarkers

We evaluated effects of antiretroviral (ARV) therapy and lipid-based nutrient supplements (LNSs) on iron, copper, and zinc in milk of exclusively breastfeeding HIV-infected Malawian mothers and their correlations with maternal and infant biomarkers. Human milk and blood at 2, 6, and 24 weeks post-partum and blood during pregnancy (≤30 weeks gestation) were collected from 535 mothers/infant-pairs in the Breastfeeding, Antiretrovirals, and Nutrition study. The participants received ARV, LNS, ARV and LNS, or no intervention from 0 to 28 weeks post-partum. ARVs negatively affected copper and zinc milk concentrations, but only at 2 weeks, whereas LNS had no effect. Among all treatment groups, approximately 80-90% of copper and zinc and <50% of iron concentrations met the current adequate intake for infants at 2 weeks and only 1-19% at 24 weeks. Pregnancy haemoglobin was negatively correlated with milk iron at 2 and 6 weeks (r = -.18, p < .02 for both). The associations of the milk minerals with each other were the strongest correlations observed (r = .11-.47, p < .05 for all); none were found with infant biomarkers. At 2 weeks, moderately anaemic women produced milk higher in iron when ferritin was higher or TfR lower. At 6 weeks, higher maternal α-1-acid glycoprotein and C-reactive protein were associated with higher milk minerals in mildly anaemic women. Infant TfR was lower when milk mineral concentrations were higher at 6 weeks and when mothers were moderately anaemic during pregnancy. ARV affects copper and zinc milk concentrations in early lactation, and maternal haemoglobin during pregnancy and lactation could influence the association between milk minerals and maternal and infant iron status and biomarkers of inflammation.

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.

A Review of Dietary Zinc Recommendations

BACKGROUND

Large discrepancies exist among the dietary zinc recommendations set by expert groups.

OBJECTIVE

To describe the basis for the differences in the dietary zinc recommendations set by the World Health Organization, the US Institute of Medicine, the International Zinc Nutrition Consultative Group, and the European Food Safety Agency.

METHODS

We compared the sources of the data, the concepts, and methods used by the 4 expert groups to set the physiological requirements for absorbed zinc, the dietary zinc requirements (termed estimated and/or average requirements), recommended dietary allowances (or recommended nutrient intakes or population reference intakes), and tolerable upper intake levels for selected age, sex, and life-stage groups.

RESULTS

All 4 expert groups used the factorial approach to estimate the physiological requirements for zinc. These are based on the estimates of absorbed zinc required to offset all obligatory zinc losses plus any additional requirements for absorbed zinc for growth, pregnancy, or lactation. However, discrepancies exist in the reference body weights used, studies selected, approaches to estimate endogenous fecal zinc (EFZ) losses, the adjustments applied to derive dietary zinc requirements that take into account zinc bioavailability in the habitual diets, number of dietary zinc recommendations set, and the nomenclature used to describe them.

CONCLUSIONS

Estimates for the physiological and dietary requirements varied across the 4 expert groups. The European Food Safety Agency was the only expert group that set dietary zinc recommendations at 4 different levels of dietary phytate for adults (but not for children) and as of yet no tolerable upper intake level for any life-stage group.

Zinc and infant nutrition

Zinc is essential for a wide variety of cellular processes in all cells. It is a critical dietary nutrient, particularly in the early stages of life. In the early neonatal period, adequate sources of zinc can be obtained from breast milk. In rare circumstances, the mammary gland produces zinc deficient milk that is potentially lethal for exclusively breast-fed infants. This can be overcome by zinc supplementation to the infant. Alterations to key zinc transporters provide insights into the mechanisms of cellular zinc homeostasis. The bioavailability of zinc in food depends on the presence of constituents that may complex zinc. In many countries, zinc deficiency is a major health issue due to poor nourishment. Young children are particularly affected. Zinc deficiency can impair immune function and contributes to the global burden of infectious diseases including diarrhoea, pneumonia and malaria. Furthermore, zinc deficiency may extend its influence across generations by inducing epigenetic effects that alter the expression of genes. This review discusses the significance of adequate zinc nutrition in infants, factors that influence zinc nutrition, the consequences of zinc deficiency, including its contribution to the global burden of disease, and addresses some of the knowledge gaps in zinc biology.

A pilot study of synbiotic supplementation on breast milk mineral concentrations and growth of exclusively breast fed infants

Despite the crucial role of breast milk mineral contents for health and growth of the infants, they decrease with the duration of lactation. So, this pilot study aimed to determine the effects of synbiotic supplementation on breast milk mineral composition and infants' growth. In this pilot, randomized, double-blind, placebo-controlled trial, 57 lactating mothers were randomly divided into two groups to receive a daily supplement of synbiotic (n=30) or a placebo (n=27) for 30 days. Breast milk zinc, copper, Iron, magnesium and, calcium concentrations were determined by flame atomic absorption spectrometry. Weight for age Z-score (WAZ) and height for age Z-score (HAZ) were assessed for infants. Dietary intake was collected from lactating women using the 24-h recall method. Data analyses were carried out using nutritionist IV, Epi Info and SPSS soft wares. Synbiotic supplementation led to an insignificant increase of the mean breast milk levels of zinc (from 2.44±0.65 to 2.55±0.55mgL(-1)), copper (from 0.35±0.24 to 0.40±0.26mgL(-1)), iron (from 0.28±0.42 to 0.31±0.38mgL(-1)), magnesium (from 17.14±1.35 to 17.17±1.09mgL(-1)), and calcium (from 189±25.3 to 189.9±21.7mgL(-1)); whilst in the placebo group, these variables decreased significantly (P=0.001). The observed changes between two groups were statistically significant (P<0.05). Although WAZ and HAZ of infants increased slightly in the supplemented group (from 1.19±0.79 to 1.20±0.69 and 0.36±0.86 to 0.37±0.85 respectively), these two parameters decreased in the placebo group which was significant only for WAZ (P=0.01). Moreover, no significant association was found between mineral intake and breast milk mineral contents. It seems, synbiotic supplementation may have positive effects on breast milk mineral contents.

Distinct response of lactating and nonlactating rats exposed to inorganic mercury on hepatic δ-aminolevulinic acid dehydratase activity

This study investigated if lactating and nonlactating rats presented differences in relation to hepatic sensitivity to HgCl2 and the potential preventive role of ZnCl2. Lactating (days 3-12 of lactation) and nonlactating rats received 27 mg/kg ZnCl2 for five consecutive days and 5 mg/kg HgCl2 for five subsequent days. Lactating and nonlactating rats exposed to HgCl2 presented a decrease in food intake, a decrease in plasma alanine aminotransferase (ALT), and an increase in hepatic Hg levels when compared to the control group. Only lactating rats exposed to HgCl2 presented an increase in hepatic δ-aminolevulinic acid dehydratase activity. On the other hand, only nonlactating rats exposed to HgCl2 presented an increase in plasma aspartate aminotransferase (AST). ZnCl2 pre-exposure partially protected the increase in plasma AST activity presented by nonlactating rats and potentiated the liver Hg accumulation in lactating rats. Pups from the Sal-Hg and Zn-Hg groups showed a decrease in absolute liver weight and an increase in liver Hg levels. Summarizing, this study demonstrated that lactating rats presented distinct biochemical responses compared to nonlactating rats exposed to HgCl2 when hepatic parameters were evaluated.

Zinc transferred through breast milk does not differ between appropriate- and small-for-gestational-age, predominantly breast-fed Bangladeshi infants

Information is needed on breast milk zinc concentration and amount of zinc transferred to the infant in relation to the time since birth for both appropriate-for-gestational-age (AGA) and small-for-gestational-age (SGA) infants. Breast milk zinc concentration and total milk volume were measured among mothers of AGA and SGA infants, using deuterium oxide "dose-to-mother" tracer technique and plasma zinc concentrations of mothers and infants. Forty-six mother-infant pairs (20 AGA and 26 SGA infants) were recruited from a low-income community in Bangladesh. Each mother-infant pair was studied 3 times: at 4, 12, and 24 wk postpartum. During each round, 2-wk studies of breast milk transfer were performed, using deuterium oxide dose-to-mother tracer technique. Breast milk samples were collected on days 1 and 5 of each round to determine milk zinc concentration. Mean ± SD birth weight and length were 3.02 ± 0.2 kg and 0.482 ± 0.012 m, respectively, for AGA and 2.34 ± 0.20 kg and 0.462 ± 0.011 m, respectively, for SGA infants, and both variables were different between groups (birth weight, P < 0.001; length, P < 0.001). Breast milk intake increased gradually with time postpartum in both groups. Breast milk zinc concentration decreased with increasing infant age (P < 0.001) but did not differ for mothers of AGA and SGA infants. Breast milk zinc transfer decreased significantly with age in both groups (P < 0.001) but did not differ by birth-weight category. Breast milk zinc concentration among Bangladeshi mothers and patterns of change at 24 wk were similar to those of wealthier countries, and there was no relation between infant birth-weight category and milk zinc concentration or transfer. This trial was registered at www.clinicaltrials.gov as NCT01728766.

Nutrient transport in the mammary gland: calcium, trace minerals and water soluble vitamins

Milk nutrients are secreted by epithelial cells in the alveoli of the mammary gland by several complex and highly coordinated systems. Many of these nutrients are transported from the blood to the milk via transcellular pathways that involve the concerted activity of transport proteins on the apical and basolateral membranes of mammary epithelial cells. In this review, we focus on transport mechanisms that contribute to the secretion of calcium, trace minerals and water soluble vitamins into milk with particular focus on the role of transporters of the SLC series as well as calcium transport proteins (ion channels and pumps). Numerous members of the SLC family are involved in the regulation of essential nutrients in the milk, such as the divalent metal transporter-1 (SLC11A2), ferroportin-1 (SLC40A1) and the copper transporter CTR1 (SLC31A1). A deeper understanding of the physiology and pathophysiology of these transporters will be of great value for drug discovery and treatment of breast diseases.

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.

Marginal maternal zinc deficiency in lactating mice reduces secretory capacity and alters milk composition

Dietary analysis predicts that marginal Zn deficiency is common in women of reproductive age. The lack of reliable biomarkers limits the capacity to assess Zn status and consequently understand effects of maternal Zn deficiency. We determined effects of marginal maternal Zn deficiency on mammary gland function, milk secretion, and milk composition in mice. Mice (n = 12/diet) were fed marginal (ZD; 15 mg Zn/kg diet) or adequate (ZA; 30 mg Zn/kg diet) Zn diets for 30 d prior to conception through mid-lactation. Mice fed the ZD had a higher plasma Zn concentration (~20%; P < 0.05) but lower milk Zn concentration (~15%; P < 0.05) compared with mice fed the ZA. ZnT2 abundance was higher (P < 0.05) in mice fed the ZD compared with mice fed the ZA; no effect on ZnT4 abundance was detected. The Zn concentration of mammary gland mitochondria tended to be ~40% greater in mice fed ZD (P = 0.07); this was associated with apoptosis and lower milk secretion (~80%; P < 0.01). Total milk protein was ~25% higher (P < 0.05), although the abundance of the major milk proteins (caseins and whey acidic protein) was lower (P < 0.05) in mice fed the ZD. Proteomic analysis of milk proteins revealed an increase (P < 0.05) in four proteins in mice fed the ZD. These findings illustrate that marginal maternal Zn deficiency compromises mammary gland function and milk secretion and alters milk composition. This suggests that lactating women who consume inadequate Zn may not produce and/or secrete an adequate amount of high quality milk to provide optimal nutrition to their developing infant.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Zinc status and growth of Korean infants fed human milk, casein-based, or soy-based formula: three-year longitudinal study

To evaluate the effect of feeding methods on growth and zinc nutritional status of infants early in life, we monitored from birth to 36 months in 51 infants who were exclusively fed human milk (HM, n = 20), casein-based formula (CBF, n = 12), or soy-based formula (SBF, n = 19) during the first five months of life. Zinc status was assessed by analyzing serum zinc concentrations and zinc intakes. Zinc contents in HM and formulas were measured. Zinc intake was estimated by weighing infants before and after feeding in the HM group and by collecting formula-intake records in the CBF and SBF groups. After solid foods were introduced, all foods consumed were also included to estimate zinc intake. The growth of infants in all groups was similar to that established for normal Korean infants. Human milk zinc concentrations declined as lactation progressed. Zinc concentrations in all formulas tested in this study were higher than HM and were also higher than those claimed by the manufacturers. During the first twelve months, mean serum zinc concentrations of infants were similar in all groups, although infants in the HM group consistently had the lowest zinc intake among the groups, and the overall zinc intake in infants fed SBF was highest. This finding could be explained by the different zinc bioavailability of HM and formulas. In conclusion, infants fed HM, CBF or SBF has normal growth up to three years of age, although HM contained the lowest zinc concentration followed by CBF, then SBF.

Association between zinc, copper, and iron concentrations in breast milk and growth of healthy infants in Tabriz, Iran

The aims of this study were to determine the effect of breast milk zinc, copper, and iron concentrations on infants' growth and their possible correlations with maternal dietary intake. Milk samples and information on food intake were collected from 182 lactating women. Concentrations of zinc, copper, and iron in milk were analyzed using atomic absorption spectrophotometry. The infant's weight for age Z-score (WAZ) and height for age Z-score (HAZ) were calculated. The mean milk zinc, copper, and iron concentrations were 1.85 +/- 0.5, 0.53 +/- 0.3, and 0.85 +/- 0.2 mg/l, respectively. Only zinc mean level was lower than the recommended range. Association between zinc, copper, and iron concentrations of milk and WAZ or HAZ of infants were not significant. However, the WAZ of infants whose mothers' milk zinc was more than 2 mg/l was significantly (P < 0.039) higher than for others. The mean dietary zinc (5.31 +/- 2.3 mg/day) and copper (1.16 +/- 0.7 mg/day) intake of mothers was significantly less than the required daily intake (RDA) recommendations (P < 0.05). The mean dietary iron intake (11.8 +/- 8.2 mg/day) was significantly higher than RDA recommendation (P < 0.001). No significant association was found between maternal mean dietary zinc, copper, and iron intakes with their concentrations in milk. Dietary consultation or/and zinc supplementation is suggested for lactating women and infants.

Breast milk macro- and micronutrient composition in lactating mothers from suburban and urban Shanghai

AIM

The objective of this study was to measure and compare the macro- and micronutrient composition of breast milk in urban and suburban lactating mothers living in Shanghai, China.

METHODS

Primiparous women residing in three urban regions (n= 30/region) and a suburban area of Shanghai (n= 30) were recruited. Breast milk samples were collected 8-10 days postpartum and dietary intake was determined.

RESULTS

Women from the suburban area were of lower socio-economic status as indicated by levels of education, occupation and income. With the exception of carbohydrates, mothers in all urban areas had significantly higher macronutrient intake levels than suburban area mothers. Sodium, potassium, phosphorus and calcium intake levels were significantly lower in suburban compared to all urban women. Concentrations of protein, lipids, copper, sodium, potassium, chlorine, zinc, manganese, phosphorus and iron were all significantly lower in milk obtained from suburban compared to urban women. Concentrations of carbohydrates in milk from suburban women were significantly higher than concentrations in than two of the three urban groups. Offspring from women in Chongming county gained significantly less weight between birth and 6 months than did offspring born to women from the three other counties.

CONCLUSIONS

In summary, there were significant differences in macro- and micronutrient intake levels and breast milk concentrations between women from urban and suburban Shanghai. These differences may have important implications for the growth and development of breastfed infants.

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.

Maternal milk concentration of zinc, iron, selenium, and iodine and its relationship to dietary intakes

The dietary intake of zinc (Zn), iron (Fe), selenium (Se), and iodine (I) of 31 lactating Mexican-American women attending the Hidalgo County WIC program in Rio Grande Valley (RGV), Texas was estimated from 24-h dietary recall interviews. Milk samples were obtained from lactating mothers who had infants 3 months of age and younger. Milk samples were collected in two visits to assess change in breast milk composition after 1-3 months postpartum: group A--after 30-45 days and group B--75-90 days. Dietary intakes indicated that the study participants had significantly inadequate percent energy intakes than the DRI (Dietary Recommended Intakes) percent recommended kilocalorie values but protein intakes were substantially higher than the percent recommended values. The estimated percent Zn, Fe, Se, and I intakes were also significantly lower than the DRI percent recommended values. The lactating mothers consumed significantly less Zn, Se, and I when compared to the Recommended Dietary Allowances (RDA) even though Fe intake was higher than the RDA value. Breast milk concentration of Zn, Fe, and Se were in agreement within the range of representative values for Constituents of Human Milk but I has significantly less concentration than the representative value. There was no statistically significant correlation observed between dietary intake and milk concentration of Zn, Fe, Se, and I. This study compares the estimated dietary intake of zinc, iron, selenium, and iodine to the concentration of these trace elements in the maternal milk of lactating women of Mexican-American heritage who attend the Rio Grande Valley WIC clinic.

Effects of dietary zinc supplement during lactation on longitudinal changes in plasma and milk zinc concentration

Effects of dietary zinc supplement during lactation on maternal zinc plasma and milk zinc concentration through 5 months of lactation were examined. One hundred and thirty eight healthy lactating mothers received a weekly 100 mg elemental zinc supplement (ZS, n = 67) or placebo (PG, n = 71) starting one week postpartum in a double blind, randomized design. Milk and plasma zinc concentrations were determined by atomic absorption spectrophotometer. During the course of study, there was not a significantly difference between ZG and PG groups in dietary zinc and energy intake. The mean plasma zinc concentration at 1st week and 5th month were 134 +/- 49.1 and 115.6 +/- 23 microg dL(-1) (PV = 0.005) for PG group, respectively; that of the ZG group these figures were 124.9 +/- 52.8 and 121 +/- 27.1 microg dL(-1) (PV = 0.38), respectively. The mean serum alkaline phosphatase concentration at 1st week and 5th month were 94.8 +/- 37 and 92.6 +/- 29.9 iu L(-1) for PG group, respectively; that of the ZG group these fissures were 90.5 +/- 36 and 90 +/- 29 iu L(-1) (PV = 0.21), respectively. Milk zinc concentration declined significantly over the course of study for two groups, with the sharpest decline occurring during the first 2 months. The mean monthly zinc concentration of ZG group declined from 310 +/- 138 at 1st week to 118 +/- 64 microg dL(-1) at 5th month (declined by 52%). Corresponding means for PG group were 322 +/- 161 and 109 +/- 70 microg dL(-1) (declined by 60%), respectively. Milk zinc concentration significantly different between two groups at 3 and 4 months. A similar study, however, with different zinc dose and administration manner, in zinc marginal deficient lactating mothers is needed to assess the impact of zinc supplementation on milk zinc concentrations.

Breast milk levels of zinc and omega-6 polyunsaturated fatty acids and growth of healthy Chinese infants

AIM

To examine the concentrations of zinc and omega-6 polyunsaturated fatty acids (omega-6 PUFAs) in breast milk, the impact of zinc on omega-6 PUFA metabolism, and the growth rate of infants.

METHODS

Forty-one mother-term infant pairs from a rural area of northern Beijing, China, who were 1 month (n = 18, group I) and 3 months (n = 23, group II) old and exclusively breastfed, were studied. The dietary records and the concentrations of zinc and omega-6 PUFAs in the milk of lactating women and the increase in weight and length of their infants during 1 and 3 postnatal months were analysed.

RESULTS

The dietary intakes of mothers in the two groups were the same, i.e. high in carbohydrate and low in fat, protein and energy. The maternal zinc intake was 7.5mg/d and thus reached only 34.6% of the current Recommended Nutrient Intake (RNI). The levels of zinc and arachidonic acid (AA, C20:4 omega-6) in the milk of group I were significantly higher than those in group II. Furthermore, significant positive correlations were found between the concentrations of zinc and AA in the breast milk and between the level of milk AA and weight gain.

CONCLUSION

Zinc may be a co-factor and essential for essential fatty acids (EFA) metabolism. Thus suboptimal zinc intake may cause EFA imbalance. Further studies of Chinese rural mother-infant pairs are necessary to determine whether zinc supplementation should be recommended when lactation exceeds 3 months.

Day-to-day variations in iron, zinc and copper in breast milk of Guatemalan mothers

OBJECTIVE

To assess the within-subject and between-subject coefficients of variation (CV) of iron, zinc and copper concentrations in the milk of Guatemalan mothers.

METHODS

We performed a cross-sectional study in lactating women who had delivered a healthy infant 1 to 6 months previously in two low-income peri-urban areas (San Bartolome Milpas Altas and Ciudad Peronia) and a low-income rural area (San Juan Chamelco) in Guatemala. Women infested with Ascaris lumbricoides or Trichuris trichiura received a single dose of albendazole (400 mg) or placebo. Two weeks after treatment, milk samples were collected on 3 or 4 consecutive days. Trace element concentrations in milk were measured by inductively coupled plasma/atomic emission spectrometry.

RESULTS

The instrumental error of the inductively coupled plasma/atomic emission spectrometry method, expressed as SD, was 0.04, 0.27 and 0.02 mg/L for iron, zinc and copper, respectively. Concentrations in milk samples collected from 47 mothers on 3 or 4 consecutive days, expressed as mean +/- SD, were 0.28 +/- 0.13, 2.03 +/- 0.37 and 0.29 +/- 0.07 mg/L for iron, zinc and copper, respectively. The within-subject CV was 46.1%, 18.2%, and 22.8% and the between-subject CV was 61.2%, 48.3% and 31.7% for iron, zinc and copper, respectively. Stage of lactation, infestation with intestinal parasites and residential area had a significant influence on milk zinc, copper and iron concentrations.

CONCLUSIONS

One sample of milk is sufficient to give a reliable estimate of the zinc concentration in milk. Two samples taken on consecutive days are required for a reliable estimate of iron and copper concentrations.

Zinc homeostasis in premature infants does not differ between those fed preterm formula or fortified human milk

The objectives of this study were to compare zinc homeostasis in premature infants enterally fed with either preterm infant formula or fortified human milk; to examine interrelationships of variables of zinc homeostasis; and to examine the findings in relation to estimated zinc requirements of preterm infants. Zinc homeostasis was studied in 14 infants (8 male), with mean gestational age of 31 wk and birth weight appropriate for gestational age, who were exclusively fed either preterm formula (n = 9) or own mother's milk with human milk fortifier (n = 5). Zinc stable isotopes were administered intravenously ((70)Zn) and orally as an extrinsic label ((67)Zn) over multiple feeds for determination of fractional absorption by dual isotope tracer ratio in urine; endogenous fecal zinc was determined by isotope dilution; and exchangeable zinc pool (EZP) size was estimated from linear regression of log-transformed urine (70)Zn enrichment data. Results indicated no significant differences in the variables of zinc homeostasis between the feeding groups; data for all subjects were thus combined. Mean (+/- SD) fractional absorption was 0.26 +/- 0.07; net absorbed zinc 0.43 +/- 0.25 mg/d (0.31 +/- 0.19 mg/kg/d). Mean EZP was 20 +/- 10 mg/kg, and was positively correlated with total absorbed zinc and with net absorbed zinc. Feeding type and total absorbed zinc were significantly related to daily weight gain (p = 0.003). Current zinc intakes from fortified human milk or formula are associated with acceptable weight gain, but whether the observed net zinc absorption was optimal in the human milk group cannot be definitively determined from these data.

Maternal zinc deficiency raises plasma prolactin levels in lactating rats

There is an inverse relation between zinc (Zn) intake and plasma prolactin in men and nonpregnant women. Whether a relation exists in lactating women is unknown, despite the potential consequences of perturbations in prolactin regulation on lactation performance. We examined the effects of low Zn intake on prolactin concentration, the prolactin regulatory pathway in the pituitary gland, and lactation performance in lactating rats. Female rats were fed diets containing 7 (zinc deficient; ZD), 10 (marginally zinc deficient; MZD) or 25 mg Zn/kg (control) from 70 d preconception to lactation d 11. Rats were killed, pituitary glands dissected, and tissues and plasma collected and analyzed for prolactin concentration. Pituitary gland pituitary factor 1 (Pit-1), dopamine 2 receptor (D2R), and prolactin receptor mRNA expression were measured in the pituitary gland. Liver, mammary gland, plasma, and milk Zn were measured. Milk intake of the pups was also recorded. Plasma prolactin concentration was higher in rats fed the ZD (125.9 microg/L) diet compared with control rats (21.7 microg/L). Pituitary gland prolactin concentration was higher in rats fed the ZD diet (69.8 mg/g total protein) compared with controls (29.0 mg/g). Plasma Zn concentration was lower in rats fed the MZD and ZD diets, and mammary gland and milk Zn concentrations were lower in rats fed the ZD diet compared with control rats. Rats fed the ZD diet had lower D2R, prolactin receptor, and Pit-1 mRNA levels, whereas rats fed the MZD diet had lower prolactin receptor and Pit-1 mRNA levels compared with control rats. Milk intake was lower in pups of rats fed the MZD and ZD diets. Our results suggest that marginal Zn nutriture may compromise milk production despite increased prolactin levels. In addition, increased circulating prolactin concentration is not due to altered nursing behavior, but may be due to alterations in the prolactin regulatory pathway in the pituitary gland.

Iron, zinc, and copper concentrations in breast milk are independent of maternal mineral status

BACKGROUND

Little is known about the regulation of iron, zinc, and copper in breast milk and the transport of these minerals across the mammary gland epithelium.

OBJECTIVE

The objective was to study associations between breast-milk concentrations of iron, zinc, and copper and maternal mineral status.

DESIGN

Milk samples from 191 Swedish and Honduran mothers were collected at 9 mo postpartum. Iron, zinc, and copper concentrations were measured by atomic absorption spectrometry. Blood samples from mothers were analyzed for plasma zinc and copper and 4 indexes of iron status: hemoglobin, plasma ferritin, soluble transferrin receptors, and zinc protoporphyrin. Complementary food energy (CFE) intake was used as an inverse proxy for breast-milk intake.

RESULTS

Mean (+/-SD) breast-milk concentrations of iron were lower in the Honduran than in the Swedish mothers (0.21 +/- 0.25 compared with 0.29 +/- 0.21 mg/L; P < 0.001), and mean breast-milk concentrations of zinc and copper were higher in the Honduran than in the Swedish mothers [0.70 +/- 0.18 compared with 0.46 +/- 0.26 mg/L (P < 0.001) and 0.16 +/- 0.21 compared with 0.12 +/- 0.22 mg/L (P = 0.001), respectively]. Milk iron was positively correlated with CFE intake (r = 0.24, P = 0.001) but was not significantly correlated with any iron-status variable. Milk zinc was negatively correlated with CFE intake (r = -0.24, P = 0.001) but was not significantly correlated with maternal plasma zinc. Milk copper was not significantly correlated with CFE intake or maternal plasma copper.

CONCLUSIONS

Milk iron, zinc, and copper concentrations at 9 mo postpartum are not associated with maternal mineral status, which suggests active transport mechanisms in the mammary gland for all 3 minerals. Milk iron concentrations increase and milk zinc concentrations decrease during weaning [corrected]

Impact of zinc supplementation on diarrheal morbidity and growth pattern of low birth weight infants in kolkata, India: a randomized, double-blind, placebo-controlled, community-based study

OBJECTIVE

To assess the impact of zinc supplementation on diarrheal morbidity and growth pattern of low birth weight (LBW) infants.

METHODOLOGY

In a randomized, double-blind, placebo-controlled, community-based study conducted in the Tiljala slum of eastern Kolkata, India, between 1999 and 2001, a birth cohort of 100 LBW infants was randomly allocated into either an intervention group receiving 1 mL daily dose of 5 mg of elemental zinc as zinc sulfate in vitamin B complex-based syrup or a placebo group receiving an identical placebo of 1 mL of vitamin-based syrup from birth up to 1 completed year of age. Active weekly surveillance was conducted for detection of diarrhea. Anthropometric measurements of each child were recorded once every month as close to the child's birth date as possible. Data were analyzed by using statistical software packages SPSSPC+ 4.0 (SPSS, Inc, Chicago, IL) and Epi Info 6.0 (Centers for Disease Control and Prevention, Atlanta, GA).

RESULTS

Among the zinc-supplemented group, diarrheal incidence of 1.36 episodes per child per year were observed, whereas it was 1.93 episodes per child per year among the placebo group, giving a relative risk of 1.4 (95% confidence interval: 1.02-2.00). Linear growth and weight for age showed significant differences between the supplemented and placebo groups only at the end of 1 year. Interestingly, the impact of zinc supplementation was masked to a large extent by the protective action of breastfeeding.

CONCLUSIONS

The study showed that zinc supplementation had a beneficial impact on the incidence of diarrhea and also weight gain among LBW infants.

Zinc transporters 1, 2 and 4 are differentially expressed and localized in rats during pregnancy and lactation

Zinc metabolism is controlled within relatively restricted limits throughout the life cycle. Expression and localization of zinc transporters 1, 2 and 4 during pregnancy and lactation in small intestine, mammary gland and liver of the rat were investigated using Northern analysis, Western blotting and immunohistochemistry. In maternal tissues, zinc transporter 4 was the most widely expressed among these zinc transporters in the tissues examined. In small intestine and liver, zinc transporter 4 increased from levels found during late gestation, but zinc transporter 1 did not. Zinc transporter 2 expression in small intestine was transient, being highest around parturition, and was not detected in liver. Immunohistochemistry revealed unique patterns of zinc transporter localization at different stages of development. In the placenta, zinc transporters 1 and 4 were found concentrated along the villous visceral splanchnopleure. In the mammary gland, zinc transporter 4 was most abundant in cells surrounding the alveolar ducts and oriented to the basement lamina. All three transporters were highly expressed in neonatal small intestine, principally near the apical surface, but zinc transporters 1 and 4 increased in abundance at the basolateral surface during development. Zinc transporter 2 was oriented apically, directly adjacent to the microvilli of enterocytes. Within the intestine, expression of each transporter was limited to enterocytes. These results support a role for these transporters in maintaining an adequate zinc supply derived from the maternal diet for zinc acquisition and use by the fetus and neonate.

Concentrations of iron, copper and zinc in human milk and powdered infant formula

Concentrations of iron, copper and zinc were determined in 56 samples of mature human milk from Canarian women and 5 samples of powdered infant formula. According to the literature our data fall within the normal limits in each kind of milk. The mean concentration of Fe, Cu and Zn of powdered infant formula was significantly higher than those concentrations found in the human milks. Significant differences among the concentrations of the studied metals for the milks of considered mothers were observed. The Fe, Cu and Zn intakes of infants fed with human milk are lower than the requirements recommended by the Food and Nutrition Board (1989). However, the infants fed with powdered infant formula had consumed an adequate intake of Fe and Cu. A progressive decrease of the metal concentrations with the lactation stage was observed. The human milk obtained in spring presented Fe and Zn concentrations lower than in autumn, which could be due to changes in nutritional habits of the mothers. Age of mother and number of previous children seem to influence the Zn and Cu concentrations of human milk.

Abnormalities in zinc homeostasis in young infants with cystic fibrosis

Low plasma zinc concentrations have been reported in approximately 30% of young infants with cystic fibrosis identified by newborn screening. The objective of this study was to examine zinc homeostasis in this population by application of stable isotope methodology. Fifteen infants with cystic fibrosis (9 male, 6 female; 7 breast-fed, 8 formula-fed) were studied at a mean (+/-SD) age of 1.8 +/- 0.7 mo. On d 1, 70Zn was administered intravenously, and 67Zn was quantitatively administered with all human milk/formula feeds during the day. Three days later, a 3-d metabolic period was initiated, during which time intake was measured and complete urine and fecal collections were obtained. Fractional zinc absorption, total absorbed zinc, endogenous fecal zinc, and net absorbed zinc were measured; fecal fat excretion was also determined. Fractional absorption was significantly higher for the breast-fed infants (0.40 +/- 0.21) compared with the formula-fed group (0.13 +/- 0.06) (p = 0.01), but with the significantly higher dietary zinc intake of the formula-fed group, total absorbed zinc was higher for those receiving formula (p = 0.01). In 1 infants with complete zinc metabolic data, excretion of endogenous zinc was twofold greater for the formula-fed infants (p < 0.05); net absorption (mg zinc/d) was negative for both feeding groups: -0.04 +/- 0.52 for breast-fed; -0.28 +/- 0.57 for formula-fed. Endogenous fecal zinc losses correlated with fecal fat excretion (r = 0.89, n = 9, p = 0.001), suggesting interference with normal conservation of endogenously secreted zinc. These findings indicate impaired zinc homeostasis in this population and suggest an explanation for the observations of suboptimal zinc status in many young infants with cystic fibrosis prior to diagnosis and treatment.

Dietary supplements for the lactating mother: influence on the trace element content of milk

Milk production is a complex process where nutritional factors interact with structural hormonal and behavioural influences. In recent years important advances have been made in understanding the role of the nutritional status of lactating women on the outcome of breastfeeding. Many questions remain unanswered about the exact requirement of trace elements for lactating mothers. The effect of dietary zinc, copper and iodine supplements on the milk concentration of these micronutrients was studied. The supplementation trial employed a specific balanced nutritional supplement prepared for the nursing mothers. The study was carried out on women living in Ferrara and its surrounding area. The population under study was healthy Italian mothers, of good socioeconomic status, and their normal infants. In total, 32 women were enrolled in the study and 22 completed it. The infants (9F, 13M) were full-term, healthy singletons and were put to breast within 12 h of birth. All women who finished the study completed a 3 d dietary record. Nutrient analysis revealed the following mean daily dietary trace element intake in the lactating mothers: zinc = 12 mg, copper = 1.4 mg and iodine = 145 microg. The zinc and copper dietary intake was in agreement with the daily intake proposed for nursing Italian mothers, while the daily intake of iodine was below the recommended intake of 200 microg. The breastfeeding mothers were placed in 2 groups, with 7 primiparas and 4 multiparas per group: lactating women eating a traditional Italian diet without vitamin and mineral supplements, and lactating women enrolled in the nutrification programme and given a nutritional supplement to their traditional diet. The supplement (PerMamma Abbott) provided 20mg zinc sulfate, 2mg copper sulfate and 116 microg potassium iodide. These quantities cover about 60-90% of the recommended intake for nursing Italian mothers. Samples of 10 ml of milk were collected at 3, 30, 90d postpartum. Zinc milk concentrations declined significantly over the study period for all lactating subjects, without differences in the rate of decline between the women who started supplementation during lactation and those who did not. Copper did not change during the first month of lactation, then declined at day 90 in supplemented and unsupplemented women, without significant differences between the two groups. An early sharp decline in milk iodine occurred in all lactating subjects, independently of iodine supplementation. After the first month of lactation breast milk iodide levels remained stable in all subjects under study. No significant differences between the two study groups were observed. The lack of correlation between the iodide level in breast milk and maternal dietary intake of iodine is not in agreement with previously published reports. The present results indicate that in healthy, well-nourished lactating Italian women, whose diet is adequate, the levels of zinc, copper and iodine in milk are not influenced by short-term supplementary intakes and that the milk levels of the trace elements studied are maintained over different levels of intake. Further research and examination by longitudinal studies are needed to establish the exact relationship between the amount of iodine furnished to the nursing mother and the iodine content of human milk. The role of compensatory homeostatic mechanisms which act during lactation needs further consideration and closer scrutiny.

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.

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).

Zinc homeostasis in breast-fed infants

The needs for dietary zinc are adequately met by most fully breast-fed infants despite relatively low zinc intakes in relation to estimated requirements. The objective of this study was to use stable isotope techniques to evaluate how zinc retention is achieved in normal fully breast-fed infants. Nine male infants, aged 2-5 mo, were fed expressed human milk labeled with 70Zn over a 24-h period. Complete fecal collections were obtained for 8 d. On d 4-7, a metabolic period was initiated which included test weighing and milk sampling, to measure zinc intake, and daily urine collections. Isotopic enrichment of fecal and urine samples was determined by fast atom bombardment mass spectrometry. Results included a mean (+/- SD) dietary zinc intake of 17.8 +/- 6.6 mumol/d; fractional absorption of 0.54 +/- 0.075; and total absorbed zinc of 9.5 +/- 3.5 mumol/d. Mean endogenous fecal zinc, determined on seven infants by isotope dilution, was 4.7 +/- 2.3 mumol/d, which resulted in a mean net absorption of 4.8 +/- 3.4 mumol/d. The results of the study indicated that, for fully breast-fed infants, it is the combination of a relatively high fractional absorption and efficient conservation of intestinal endogenous zinc that results in zinc retention adequate to meet the demands of growth in the face of modest intake.

Daily dietary intake of copper, zinc, and selenium of exclusively breast-fed infants of middle-class women in Burundi, Africa

Copper (Cu), zinc (Zn), and selenium (Se) in human milk of middle-class Burundian women during the first 10 mo of lactation have been determined. Wet acid digestion, using nitric and perchloric acids, and atomic absorption spectrometric analysis have been used. Daily intakes have been calculated and proven to decrease from 0.39 +/- 0.05 (colostrum) to 0.16 +/- 0.02 (mature milk), 2.3 +/- 0.3 (colostrum), to 1.2 +/- 0.2 mg (mature milk) and 10.9 +/- 1.5 (colostrum) to 5.3 +/- 0.8 micrograms (mature milk) for Cu, Zn, and Se, respectively. Since values for this African country are nonexistent, intake levels are compared with literature data and found to be somewhat higher than those observed in other poorly nourished countries. The recommended safe and adequate daily intake for infants of 0-6 mo of age, as proposed by the National Research Council of the USA, is only met for Burundian infants < 1 mo of age. The function of copper (Cu) and zinc (Zn) as essential trace elements has been known for quite a number of years (1). Also, selenium (Se) is a trace element essential for the activity of glutathione peroxidase (2) and type I iodothyronine 5-deiodinase (3). For all three elements, an adequate intake is necessary for satisfactory infant growth and development (4). In view of the almost total lack of relevant data on Burundi (Africa), we have determined Cu, Zn, and Se in human milk of middle-class Burundian women during the first 10 mo of lactation (5). The aim of this study is to assess infants' elemental intake for this country and compare this with literature data on trace elemental intake of exclusively breast-fed infants.

Breast milk as a source of vitamins, essential minerals and trace elements

Human breast milk provides all of the vitamins and essential minerals and trace elements (micronutrients) that are required by the normal term infant, until weaning. With a few exceptions, excessive micronutrient supplies to the mother, or a moderate deficiency in her diet, do not greatly alter the supply to the infant. Thus, the infant is well-protected by maternal homeostatic processes, although the mechanisms of these are not yet well understood. Considerable progressive changes in concentration occur for some of the micronutrients during the course of lactation. Because the concentration of these nutrients, and of other substances that modify their absorption by the infant, such as binding proteins, differs considerably between human milk, animal milk and, hence, commercial milk formulae, there is great interest in the quantitative significance of micronutrient supplies, and their variability in breast milk, in the quest for improvement of commercial formulations. The aim of this review is to summarize the available information about the factors that determine breast milk contents of micronutrients.

Lactation--how important is it?

In Africa, with poverty rising, and health care diminishing, a nutritional question is-what are the limits of successful physiological adaptation to low dietary intakes? In this review the practice of lactation is discussed, from both past and present viewpoints. Orthodox Recommended Allowances for lactation are scarcely ever met. Yet, through various adaptations, the huge majority of African and similarly placed mothers lactate successfully and produce milk of good quantity and quality. The benefits from supplements are discussed; broadly, results have been disappointing. Some good and adverse non-dietary practices are considered. Benefits for infant and mother from lactation, even for protracted periods, far exceed drawbacks.

Growth and intakes of energy and zinc in infants fed human milk

The objectives of this study were to examine the growth pattern of healthy infants who were fed human milk exclusively for > or = 5 months and its relationship to intakes of milk, energy, and zinc. Monthly anthropometric measurements were obtained on 71 infants through 7 months of age and on 43 through 9 months. Milk zinc concentrations were determined and milk intake was measured by 3-day test weighing. Mean (+/- SD) calculated energy intake from human milk was 106 +/- 20, 79 +/- 11, 70 +/- 10, and 57 +/- 12 kcal/kg per day at 2 weeks and 3, 5, and 7 months of age, respectively; intake from milk plus solids was 70 +/- 13 kcal/kg at 7 months. Zinc intakes from human milk were 2.3 +/- 0.68, 1.0 +/- 0.43, 0.81 +/- 0.42, and 0.52 +/- 0.31 mg/day at these points. The maximum mean weight-for-age percentile for both sexes was 62 at 2 months; the mean percentile declined to 33 by 7 months and to 25 by 9 months of age. Mean length-for-age percentile declined from 43 at 2 weeks of age to 28 and 26 by 7 and 9 months of age, respectively. Energy intake at 2 weeks of age was positively associated with the weight increment from 2 weeks to 7 months of age (p = 0.003) and with a change in weight-for-age z scores from 2 weeks to 3 months of age (p = 0.028). Mean energy intakes of healthy breast-fed infants are lower through the first 7 months of life than current recommendations. Zinc intakes of breast-fed infants are likely to be adequate, on average, through 5 months of breast-feeding but subsequently are marginal without the introduction of weaning foods. Revision of standards for growth based on observations in breast-fed infants may be appropriate, but the possibility of growth-limiting nutrient deficiencies should also be investigated.

Competition of Mn2+ and Zn2+ with 59Fe2+ and 59Fe3+ for the plasma membrane receptors from lactating mouse mammary gland

Nonlabeled MnCl2 and ZnSO4 compete with 59Fe(2+)-ascorbate and 59Fe2(3+)O3 for transport binding sites situated on the plasma membranes of lactating mouse mammary gland cells. The binding was found to be a process reaching saturation. The heterologous competition used here ruled out the participation of transferrin and to propose that Fe, Mn, and Zn are transported from blood to milk by a mechanism involving one receptor during lactation. Further experiments are necessary to establish the details of the transport mechanism.

The role of zinc in reproduction. Hormonal mechanisms

Zinc is a very important element in the reproductive cycle of species. In humans, it is necessary for the formation and maturation of spermatozoa, for ovulation, and for fertilization. During pregnancy, zinc deficiency causes a number of anomalies: spontaneous abortion, pregnancy-related toxemia, extended pregnancy or prematurity, malformations, and retarded growth. Delivery is adversely affected by deficiency. These different effects of zinc can be explained by its multiple action on the metabolism of androgen hormones, estrogen and progesterone, together with the prostaglandins. Nuclear receptors for steroids are all zinc finger proteins. Zinc supplementation has already proven beneficial in male sterility and in reducing complications during pregnancy. However, it would be worth conducting larger-scale trials to confirm these beneficial effects.