Zinc requirements and zinc intakes of breast-fed infants

Are boys more vulnerable to stunting? Examining risk factors, differential sensitivity, and measurement issues in Zambian infants and young children

BACKGROUND

Stunting remains a considerable public health problem globally, and sex differences in prevalence have been documented. While many risk factors for stunting have been identified, few studies examine how these factors may contribute to sex differences. We test whether: (1) boys and girls are differentially exposed to stunting risk factors, (2) boys and girls respond differently to similar exposures, and (3) these associations are sensitive to the growth measures used.

METHODS

Data comes from 7486 Zambian infants, aged 0-23 months, participating in the SUN (Scaling Up Nutrition) 2.0 Program baseline survey. Surveys and dietary recalls were collected from primary caregivers, and anthropometry was collected for caregivers and children. Stunting was defined as height-for-age z-score (HAZ) <-2. Descriptive statistics and adjusted multilevel logistic regression models controlling for age and province were used to identify sex differences in exposures and risk factors for stunting, respectively. Interaction terms between exposure and infant sex were added to test for sex differences in response. Sensitivity testing with alternate measures of infant size, including height-for-age difference (HAD), was conducted.

RESULTS

Boys were more likely to be stunted than girls (34.5% vs. 25.7%, respectively). Numerous maternal, care giving, diet, and household characteristics were associated with the risk of stunting, but few sex differences were seen in exposure to these factors. Only one risk factor-maternal marital status-showed evidence of moderation by sex at the p < 0.05 level, while a limited number of risk factors did so at the p < 0.10 level. At all ages, boys were longer than girls, and there were no sex-specific differences in the patterns of HAZ or HAD with age. Results were robust to alternate specifications.

CONCLUSIONS

Our results show that Zambian boys have lower mean HAZ scores than girls and a greater prevalence of stunting throughout the first two years We do not find strong evidence that infant feeding practices, environmental exposures, or care giving differ consistently between boys and girls or that boys and girls respond differently to these exposures. Our results instead indicate that further investigation of prenatal factors and/or measurement issues is needed.

Zinc - a scoping review for Nordic Nutrition Recommendations 2023

Zinc is essential for several biological processes including those critical for the immune system, DNA synthesis, cell division, and growth. Zinc is involved in the pathophysiology of chronic diseases and protects proteins and lipids from oxidative damage. Inadequate zinc intake and low plasma zinc concentration are associated to an increased risk of chronic diseases such as cardiovascular diseases and type 2 diabetes; however, the evidence is limited. Zinc deficiency increases the risk of infections and poor growth and may contribute to the high burden of infectious diseases and stunting in children living in low- and middle-income countries. The risk of zinc deficiency in the populations of the Nordic and Baltic countries is low.

The Safe and Effective Use of Plant-Based Diets with Guidelines for Health Professionals

Plant-based diets, defined here as including both vegan and lacto-ovo-vegetarian diets, are growing in popularity throughout the Western world for various reasons, including concerns for human health and the health of the planet. Plant-based diets are more environmentally sustainable than meat-based diets and have a reduced environmental impact, including producing lower levels of greenhouse gas emissions. Dietary guidelines are normally formulated to enhance the health of society, reduce the risk of chronic diseases, and prevent nutritional deficiencies. We reviewed the scientific data on plant-based diets to summarize their preventative and therapeutic role in cardiovascular disease, cancer, diabetes, obesity, and osteoporosis. Consuming plant-based diets is safe and effective for all stages of the life cycle, from pregnancy and lactation, to childhood, to old age. Plant-based diets, which are high in fiber and polyphenolics, are also associated with a diverse gut microbiota, producing metabolites that have anti-inflammatory functions that may help manage disease processes. Concerns about the adequate intake of a number of nutrients, including vitamin B12, calcium, vitamin D, iron, zinc, and omega-3 fats, are discussed. The use of fortified foods and/or supplements as well as appropriate food choices are outlined for each nutrient. Finally, guidelines are suggested for health professionals working with clients consuming plant-based diets.

Zinc Signaling in the Mammary Gland: For Better and for Worse

Zinc (Zn²⁺) plays an essential role in epithelial physiology. Among its many effects, most prominent is its action to accelerate cell proliferation, thereby modulating wound healing. It also mediates affects in the gastrointestinal system, in the testes, and in secretory organs, including the pancreas, salivary, and prostate glands. On the cellular level, Zn²⁺ is involved in protein folding, DNA, and RNA synthesis, and in the function of numerous enzymes. In the mammary gland, Zn²⁺ accumulation in maternal milk is essential for supporting infant growth during the neonatal period. Importantly, Zn²⁺ signaling also has direct roles in controlling mammary gland development or, alternatively, involution. During breast cancer progression, accumulation or redistribution of Zn²⁺ occurs in the mammary gland, with aberrant Zn²⁺ signaling observed in the malignant cells. Here, we review the current understanding of the role of in Zn²⁺ the mammary gland, and the proteins controlling cellular Zn²⁺ homeostasis and signaling, including Zn²⁺ transporters and the Gq-coupled Zn²⁺ sensing receptor, ZnR/GPR39. Significant advances in our understanding of Zn²⁺ signaling in the normal mammary gland as well as in the context of breast cancer provides new avenues for identification of specific targets for breast cancer therapy.

Infant Complementary Feeding of Prebiotics for theMicrobiome and Immunity

Complementary feeding transitions infants from a milk-based diet to solid foods, providing essential nutrients to the infant and the developing gut microbiome while influencing immune development. Some of the earliest microbial colonisers readily ferment select oligosaccharides, influencing the ongoing establishment of the microbiome. Non-digestible oligosaccharides in prebiotic-supplemented formula and human milk oligosaccharides promote commensal immune-modulating bacteria such as Bifidobacterium, which decrease in abundance during weaning. Incorporating complex, bifidogenic, non-digestible carbohydrates during the transition to solid foods may present an opportunity to feed commensal bacteria and promote balanced concentrations of beneficial short chain fatty acid concentrations and vitamins that support gut barrier maturation and immunity throughout the complementary feeding window.

A dynamic model for predicting growth in zinc-deficient stunted infants given supplemental zinc

Background

Zinc deficiency limits infant growth and increases susceptibility to infections, which further compromises growth. Zinc supplementation improves the growth of zinc-deficient stunted infants, but the amount, frequency, and duration of zinc supplementation required to restore growth in an individual child is unknown. A dynamic model of zinc metabolism that predicts changes in weight and length of zinc-deficient, stunted infants with dietary zinc would be useful to define effective zinc supplementation regimens.

Objective

The aims of this study were to develop a dynamic model for zinc metabolism in stunted, zinc-deficient infants and to use that model to predict the growth response when those infants are given zinc supplements.

Design

A model of zinc metabolism was developed using data on zinc kinetics, tissue zinc, and growth requirements for healthy 9-mo-old infants. The kinetic model was converted to a dynamic model by replacing the rate constants for zinc absorption and excretion with functions for these processes that change with zinc intake. Predictions of the dynamic model, parameterized for zinc-deficient, stunted infants, were compared with the results of 5 published zinc intervention trials. The model was then used to predict the results for zinc supplementation regimes that varied in the amount, frequency, and duration of zinc dosing.

Results

Model predictions agreed with published changes in plasma zinc after zinc supplementation. Predictions of weight and length agreed with 2 studies, but overpredicted values from a third study in which other nutrient deficiencies may have been growth limiting; the model predicted that zinc absorption was impaired in that study.

Conclusions

The model suggests that frequent, smaller doses (5-10 mg Zn/d) are more effective for increasing growth in stunted, zinc-deficient 9-mo-old infants than are larger, less-frequent doses. The dose amount affects the duration of dosing necessary to restore and maintain plasma zinc concentration and growth.

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 vegetarian diets

Well planned vegetarian diets can provide adequate amounts of zinc from plant sources. Vegetarians appear to adapt to lower zinc intakes by increased absorption and retention of zinc. Good sources of zinc for vegetarians include whole grains, tofu, tempeh, legumes, nuts and seeds, fortified breakfast cereals and dairy products. The inhibitory effects of phytate on absorption of zinc can be minimised by modern food-processing methods such as soaking, heating, sprouting, fermenting and leavening. Absorption of zinc can be improved by using yeast-based breads and sourdough breads, sprouts, and presoaked legumes. Studies show vegetarians have similar serum zinc concentrations to, and no greater risk of zinc deficiency than, non-vegetarians (despite differences in zinc intake).

Zinc deficiency in infants and children: a review of its complex and synergistic interactions

Zinc deficiency is estimated to contribute to over half a million deaths per year in infants and children under 5 years of age. This paper reviews the features of mild-to-moderate zinc deficiency, which include growth faltering, deficits in immune function and altered integrity and function of the gastro-intestinal tract. Sub-clinical features include oxidative stress and a pro-inflammatory state. The homeostatic response to low dietary zinc intake by increasing absorption is limited, especially if the source of zinc is of poor bioavailability, and conservation of endogenous intestinal losses is a critical component of adaptation. Owing to low zinc intakes, older breastfed infants, especially those of low birthweight, are predictably at risk of zinc deficiency if complementary food choices are unfortified and/or low in zinc. Host factors such as young age, poor intra-uterine zinc accretion owing to poor maternal status and/or prematurity, and gastro-intestinal dysfunction also potently predispose to zinc deficiency. Environmental enteropathy, which is prevalent in low-resource settings, may substantially impair zinc absorption and/or increase endogenous losses, and thus lead to relatively high zinc requirements. Emerging evidence highlights common features between chronic inflammation and zinc deficiency, and each may exacerbate the other. More investigations of zinc homeostasis in populations in low-resource settings are needed to better quantify absorption capacity and losses. Effective preventive strategies must address potentially higher zinc requirements as well as the underlying context that perpetuates a vicious cycle of zinc deficiency and multiple adverse outcomes.

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.

Effects of zinc supplementation on the incidence of mortality in preschool children: a meta-analysis of randomized controlled trials

Background

Previous trials have shown that zinc supplementation can decrease the risk of diarrhea, pneumonia, and malaria in children; however, the effects of zinc supplementation on mortality remain unclear. This study aimed at evaluating the benefits and risks of zinc supplementation on both total mortality and cause-specific mortality.

Methodology and Principal Findings

We searched PubMed, EmBase, and the Cochrane Central Register of Controlled Trials to identify randomized controlled trials in preschool children reporting total mortality or cause-specific mortality. Relative risk (RR) was used as a measure of the effect of zinc supplementation on the risk of mortality using a random effect model. Of the 1,520 identified articles, we included 8 trials reporting data on 87,854 children. Overall, zinc supplementation had no effect on total mortality (RR, 0.76; 95% CI: 0.56–1.04; P = 0.084), diarrhea-related mortality (RR, 0.80; 95% CI: 0.53–1.20; P = 0.276), pneumonia-related mortality (RR, 0.52; 95% CI: 0.11–2.39; P = 0.399), malaria-related mortality (RR, 0.90; 95% CI: 0.77–1.06; P = 0.196), or other causes of mortality (RR, 0.98; 95% CI: 0.67–1.44; P = 0.917). Subgroup analysis indicated that zinc supplementation was associated with a reduction in total mortality risk if the participants were boys, aged greater than 12 months, and the duration of the follow-up period was less than 12 months.

Conclusions/Significance

Zinc supplementation does not have an effect on total mortality, diarrhea-related mortality, pneumonia-related mortality, malaria-related mortality, or other causes of mortality. Subgroup analysis suggested that zinc supplementation can effectively reduce the risk of total mortality if the participants were boys, aged greater than 12 months, and the duration of the follow-up period was less than 12 months.

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.

Nutritional management of the breastfeeding dyad

Milk is successfully produced by mothers regardless of their nutritional status. Nevertheless, the concentrations of some nutrients, specifically vitamins A, D, B1, B2, B3, B6, and B12, fatty acids, and iodine, in human milk depend on or are influenced by maternal diet. A healthy and varied diet during lactation ensures adequate maternal nutrition and optimal concentration of some nutrients in human milk. Exclusive breastfeeding meets the nutritional needs of infants for 6 months of life with the exception of vitamins D and K, which should be given to breastfed infants as supplements.

Comparison of complementary feeding strategies to meet zinc requirements of older breastfed infants

BACKGROUND

The low zinc intake from human milk at ∼6 mo of age predicts the dependence on complementary foods (CF) to meet the zinc requirements of older breastfed-only infants.

OBJECTIVE

The objective of this study was to compare major variables of zinc homeostasis and zinc status in 9-mo-old breastfed infants who were randomly assigned to different complementary food regimens.

DESIGN

Forty-five exclusively breastfed 5-mo-old infants were randomly assigned to receive commercially available pureed meats, iron-and-zinc-fortified infant cereal (IZFC), or whole-grain, iron-only-fortified infant cereal (IFC) as the first and primary CF until completion of zinc metabolic studies between 9 and 10 mo of age. A zinc stable-isotope methodology was used to measure the fractional absorption of zinc (FAZ) in human milk and CF by dual-isotope ratios in urine. Calculated variables included the dietary intake from duplicate diets and 4-d test weighing, the total absorbed zinc (TAZ) from FAZ × diet zinc, and the exchangeable zinc pool size (EZP) from isotope enrichment in urine.

RESULTS

Mean daily zinc intakes were significantly greater for the meat and IZFC groups than for the IFC group (P < 0.001); only intakes in meat and IZFC groups met estimated average requirements. Mean (±SEM) TAZ amounts were 0.80 ± 0.08, 0.71 ± 0.09, and 0.52 ± 0.05 mg/d for the meat, IZFC, and IFC groups, respectively (P = 0.027). Zinc from human milk contributed <25% of TAZ for all groups. The EZP correlated with both zinc intake (r = 0.43, P < 0.01) and TAZ (r = 0.54, P < 0.001).

CONCLUSION

Zinc requirements for older breastfed-only infants are unlikely to be met without the regular consumption of either meats or zinc-fortified foods.

Proton Pump Inhibitors Interfere With Zinc Absorption and Zinc Body Stores

Background

Proton pump inhibitors (PPIs) cause a sharp elevation of gastro-duodenal luminal pH which in turn has resulted in reports of reduced absorption of magnesium and certain other nutrients.

Methods

Gastroesophageal reflux disease (GERD) patients on long-term PPI therapy (> 6 months) or healthy test subjects (not on any acid preventive or neutralizing medication) were administered oral doses of zinc gluconate (26.2 mg zinc, twice daily) for 14 days followed by 5 cc venous blood samples. Plasma was analyzed for total zinc content by atomic absorption spectrophotometry. Baseline plasma and red blood cell zinc levels were also measured in these two groups when not taking any zinc supplementation.

Results

Plasma zinc levels of healthy controls increased by 126% during the period of zinc supplementation compared to only a 37% increase for individuals on long-term PPI therapy. On their normal diet (with no zinc supplementation), PPI-users had a 28% lower plasma zinc level than healthy controls (P < 0.005).

Conclusions

PPI use dramatically reduces supplemental zinc uptake and can result in decreased zinc body stores. Certain individuals on long-term PPI therapy, such as infants being treated for colic, may be at risk for decreased systemic levels of trace metals needed for developmental, regenerative and immunological requirements.

Effects of zinc exposure on zinc transporter expression in human intestinal cells of varying maturity

OBJECTIVES

Zinc (Zn) homeostasis in adults is achieved principally through a balance between intestinal absorption and excretion involving adaptive mechanisms programmed by levels of dietary Zn. Zn absorption in infants is not as tightly regulated as that in adults, which may induce potential toxicity in infants due to the relatively high capacity of Zn absorption. We hypothesized that intestinal Zn homeostasis is developmentally regulated and depends on intestinal maturation, which in turn affects Zn transporter regulation.

MATERIALS AND METHODS

Cultured human fetal (FHs 74 Int, F) and adult (Caco-2: undifferentiated, U; differentiated, D) intestinal cells were used to determine developmental differences in Zn uptake and effects of Zn exposure on Zn transporters.

RESULTS

Zn uptake rates in F and U cells were higher compared with D cells (F, 9-fold; U, 3-fold). F cells were more intolerant to Zn exposure than were U or D cells (LD50 = 67.9 +/- 5.3; 117.0 +/- 5.2; 224.4 +/- 3.7 micromol/L, respectively). Two mechanisms were involved in developmental regulation of Zn homeostasis: differential Zn transporter expression and differential response to Zn exposure. In F cells, zinc-regulated transporter (ZRT)/iron-regulated transporter (IRT)-like protein (Zip)4 expression was undetectable; Zn (50 micromol/L) increased levels of Zn transporter (ZnT)1, ZnT2, and metallothionein-1 mRNA and ZnT1 protein. U and D cells had higher mRNA expression of ZnT1 (U: 5-fold; D: 7-fold, respectively) and ZnT2 (U: 2-fold; D: 9-fold, respectively) than F cells, and D cells also had higher Zip4 expression (3-fold) than U cells. In U cells, Zn exposure increased Zip4 protein level, but not membrane-associated abundance. However, in D cells, Zn exposure decreased both the Zip4 protein level and membrane-associated abundance.

CONCLUSIONS

Zn absorption is developmentally regulated through intestinal Zn efflux and sequestration and import mechanisms, which may be responsible for differences in Zn absorption observed between infants and adults.

Effect of zinc supplementation on mortality in children aged 1-48 months: a community-based randomised placebo-controlled trial

BACKGROUND

Studies from Asia have suggested that zinc supplementation can reduce morbidity and mortality in children, but evidence from malarious populations in Africa has been inconsistent. Our aim was to assess the effects of zinc supplementation on overall mortality in children in Pemba, Zanzibar.

METHODS

We enrolled 42,546 children aged 1-36 months, contributing a total of 56,507 child-years in a randomised, double-blind, placebo-controlled trial in Pemba, Zanzibar. Randomisation was by household. 21 274 children received daily supplementation with zinc 10 mg (5 mg in children younger than 12 months) for mean 484.7 days (SD 306.6). 21,272 received placebo. The primary endpoint was overall mortality, and analysis was by intention to treat. This study is registered as an International Standard Randomised Clinical Trial, number ISRCTN59549825.

FINDINGS

Overall, there was a non-significant 7% (95% CI -6% to 19%; p=0.29) reduction in the relative risk of all-cause mortality associated with zinc supplementation.

INTERPRETATION

We believe that a meta-analysis of all studies of mortality and morbidity, will help to make evidence-based recommendations for the role of zinc supplementation in public health policy to improve mortality, morbidity, growth, and development in young children.

Zinc-deficiency dermatitis in breast-fed infants

We report ten infants (mean gestational age: 30 weeks; range: 25 to 40 weeks) with zinc deficiency dermatitis who developed erosive, impetiginized periorificial dermatitis at 10 weeks of age (corresponding to a mean gestational age of 41.4 weeks, with a range of 36-44 weeks), but who were otherwise well. Cutaneous symptoms were initially misdiagnosed as eczema or impetigo in 8/10 (80%) children who received either topical (4/8) and/or systemic (6/8) antibiotics. Topical corticosteroids were applied in 4/10 infants for a mean time of 4 weeks (range: 2 to 5 weeks) before the correct diagnosis was established by decreased serum zinc levels; skin atrophy (telangiectasia, thinning) as a complication of topical steroid treatment (class II steroids) was observed in two infants. All children responded to oral therapy with zinc sulfate or zinc gluconate (1.5-4 mg/kg/d). Skin lesions started to clear within 24 h after the initiation of therapy and had completely cleared in all infants after 14 days of therapy (range: 3-14 days). We conclude that nutritional zinc deficiency is a frequently misdiagnosed problem in thriving, fully breast-fed preterm babies. It is attributable to the decreased zinc content of human milk as compared to cow's milk, and the increased demand of zinc in rapidly thriving preterm infants. It seems advisable to routinely check serum zinc levels in fully breast-fed preterm infants who do not receive regular oral zinc supplementation once they reach a gestational age of 40 weeks.

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.

Longitudinal study of diet and iron deficiency anaemia in infants during the first two years of life

The objectives of this study were: (i) to investigate the energy, iron, zinc, calcium and vitamin C intakes of a group of healthy term Caucasian infants resident in Dunedin, New Zealand, prospectively from age 9 months to 2 years; and (ii) to determine the prevalence of iron deficiency anaemia among these infants. A self-selected sample of 74 Caucasian mothers and their infants born in Dunedin, New Zealand, between October 1995 and May 1996 were recruited. Dietary intake was determined using estimated diet records at 9, 12, 18 and 24 months of age. Haemoglobin concentration, mean corpuscular volume andzinc protoporphyrin concentration were determined at the same ages. The infants' zinc, calcium and vitamin C intakes appeared adequate. Their median iron intakes ranged from 4.3 mg (at 12 months) to 7.0 mg (at 9 months) per day and were below estimated requirements at all ages. At 9, 12 and 18 months of age, 7% (n = 4) of the infants had iron deficiency anaemia. None of the infants had iron deficiency anaemia at 24 months. The iron intakes of this group of Caucasian infants and young children appeared inadequate. However, their rate of iron deficiency anaemia was lower than has been reported in previous New Zealand studies.

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.

The role of zinc in the growth and development of children

This review concerns the importance of zinc in growth, development, and cognitive function in children and the deleterious consequences of its deficiency on children's health. Possible strategies to overcome zinc deficiency and the results of some supplementation trials are discussed.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

Complementary feeding practices and dietary intakes from complementary foods amongst weanlings in rural Malawi

OBJECTIVE

The objectives of this study were to estimate the quantity and nutritive quality of the complementary diet in rural Malawi, and to identify feeding practices, nutrients and dietary modifiers of iron and zinc bioavailability that may limit the quality of the diet.

DESIGN

This cross-sectional study design included an anthropometric survey, a feeding practices questionnaire, and an interactive, 24 h recall dietary data survey.

SETTING

Four rural villages in Balaka district, southern Malawi.

SUBJECTS

Mothers resident in the study communities with breastfed children aged up to 24 months were eligible.

RESULTS

Stunting was prevalent among these weanlings. Maize was the predominant food source, with limited contribution of animal foods. Deficits in dietary energy and several nutrients were found when compared to estimated needs. When expressed per kg body weight, energy intakes appeared adequate. The bioavailability of zinc was low due to a high phytate:zinc molar ratio. Iron bioavailability was also low due to low intake of absorption enhancers such as meat/fish/poultry protein and ascorbic acid. Dietary quality was poorest for 6 to 8-month-old infants.

CONCLUSIONS

Iron, zinc and calcium were the most limiting nutrients to the quality of the diet, partly exacerbated by the poor bioavailability of iron and zinc. Increased total intake and bioavailability of iron and zinc would improve the complementary diets.

SPONSORSHIP

This study was funded by the Thrasher Research Fund, Salt Lake City, Utah, USA.

Food and nutrient intake in a cohort of 8-month-old infants in the south-west of England in 1993

OBJECTIVE

To investigate food and nutrient intakes in 8-month-old infants.

DESIGN

Prospective study.

SETTING

Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC), south-west England.

SUBJECTS

A total of 1131 singleton Caucasian infants (82% of those invited) from a 10% random sample of ALSPAC, known as Children in Focus (CIF).

METHODS

Diet was assessed using a structured 3-day unweighed dietary record. Food and nutrient intakes were compared with intakes from the 6--9 month age group of a British infant feeding survey, which formed part of the National Diet and Nutrition Survey (NDNS). Nutrient intakes were compared with dietary reference values (DRV).

RESULTS

Intakes of energy and most nutrients were very similar between CIF and NDNS. The main difference was in the type of fat eaten resulting in a higher polyunsaturated to saturated fatty acid ratio in CIF (0.34) compared with NDNS (0.21). Other differences included the much lower calcium and iodine intakes in CIF compared with the NDNS. Differences in the proportion of consumers of formula and cow's milk accounted for most of the nutrient differences. Energy intakes were similar to the estimated average requirements (EAR), however, breastfed infants were slightly below and non-breastfed were slightly above the EAR. Mean intakes of zinc and vitamin D were below the Reference Nutrient Intakes.

CONCLUSIONS

The diets of 8-month-old infants in this study were adequate in most nutrients. Breastfed infants had slightly lower energy intakes than non-breastfed infants.

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 zinc and iron sources, physical growth and cognitive development of breastfed infants

Iron and zinc are trace minerals that are of critical importance to the young infant for normal growth and development. Exclusive feeding of human milk provides adequate amounts of both of these nutrients for normal term infants for approximately the first 6 mo. of life. Current recommendations for introduction of complementary foods at this age do not emphasize the order of introduction of specific foods because the infant's gastrointestinal tract is considered mature at this time. Consideration of nutritional needs at 6 mo. has generally focused on the increasing risk of iron deficiency the longer the diet is without an additional source of iron. Recently, there has been more recognition of the risk of zinc deficiency in the second half of the first year of life in breastfed infants. Review of common feeding practices indicates that early complementary foods are typically iron fortified but low in zinc. Several studies have now investigated the effects of meat as an earlier complementary food on iron and zinc status. Results of these studies, although requiring further verification, suggest that increased meat intake by breastfed infants >6 mo. old would adequately support both iron and zinc requirements.

Zinc homeostasis in healthy infants fed a casein hydrolysate formula

BACKGROUND

The results of earlier, nonquantitative studies suggested that absorption of zinc from a semielemental (casein hydrolysate) formula was inferior to absorption from a cow's milk-based formula. The objective of this study was to compare fractional, total and net zinc absorption, and fecal excretion of endogenous zinc in the same healthy young infants when fed a casein hydrolysate versus cow's milk-based formula.

METHODS

Fractional absorption of zinc and fecal excretion of endogenous zinc were determined from measurement of cumulative fecal excretion of unabsorbed tracer and by an isotope dilution technique, respectively, after oral administration of a 70Zn tracer with all formula feedings for 1 day. Six infants were assigned randomly to receive the test or control formula, and the other formula was administered 2 to 5 weeks later.

RESULTS

Mean (+/-SD) fractional absorption of zinc from the casein hydrolysate formula (0.47 +/- 0.17) was double that from the cow's milk-based formula (0.22 +/- 0.04; P = 0.01) with a correspondingly greater total zinc absorption (3.23 +/- 1.67 mg Zn/day vs. 1.55 +/- 0.55 mg Zn/day; P = 0.05). Because the excretion of endogenous zinc in the feces did not differ between formulas (0.90 +/- 0.44 mg Zn/day vs. 0.91 +/- 0.29 mg Zn/day), net absorption of zinc was also higher with the casein hydrolysate formula (2.33 +/- 1.65 mg Zn/day vs. 0.81 +/- 0.67 mg Zn/day; P = 0.02).

CONCLUSIONS

Retention of zinc appeared to be adequate to meet the needs for growth during feeding with cow's milk-based formula and was more than adequate during short-term feeding with the casein hydrolysate formula.

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.

Low plasma zinc concentrations in young infants with cystic fibrosis

OBJECTIVES

The purpose of this study was to examine the zinc status of young infants with cystic fibrosis before and after the initiation of pancreatic enzyme therapy.

STUDY DESIGN

Cross-sectional data were obtained for infants with cystic fibrosis identified by newborn screening. Plasma zinc concentrations were measured and analyzed according to enzyme use at the time of the blood draw. On a subgroup of infants, zinc concentrations were determined again after several weeks with enzyme therapy.

RESULTS

Mean (+/-SD) plasma zinc concentration for the infants studied before the initiation of enzyme therapy was 10.4 +/- 2.2 micromol/L (68.3 +/- 14.7 microgram/dL) (n = 48), which was significantly lower than the mean for those receiving enzymes for >/=2 weeks, 11.8 +/- 2. 3 micromol/L (77.1 +/- 14.9 microgram/dL) (n = 15) (P =.03). For the group not yet receiving enzymes, 29% of infants had zinc concentrations in the deficient range. Data were available before and after enzyme therapy for 30 infants and indicated a mean increase of 1.64 +/- 3.0 micromol/L (10.7 +/- 19.3 microgram/dL) (P =. 005).

CONCLUSIONS

These data suggest that many of the infants were zinc deficient at the time of diagnosis. We conclude that zinc should be included among the specific micronutrients given consideration in the management of cystic fibrosis, particularly in infants.

Zinc and phytate intake of rural Gambian infants: contributions from breastmilk and weaning foods

Zinc and phytate intakes of 183 rural Gambian infants were obtained from weighed records of breastmilk and food intake and measured contents in foods. Total zinc intake of 2.7 mg/d in the first month of age declined to 1.5 mg/d at 3 months, then increased to 4.3 mg/d by 17 months. Breastmilk was an important source of zinc, but the predominant cereal and groundnut-based foods had high [phytate]/[Zn] molar ratios ranging from 13 to 28, indicating potential impaired zinc bioavailability. The [phytate]/[Zn] molar ratio for the diet as a whole was low in early infancy, but increased to 13 in the second year. In contrast, this ratio was less than 6 for the diet of 48 Cambridge breastfed infants up to 18 months. A further disadvantage to the Gambian infants was indicated by their lower intake of protein of animal origin. However, calcium intake was estimated in both communities to be below the level which could give rise to zinc chelation in association with phytate. Compared to 'basal' and 'normative' requirements, total zinc intake of the Gambian infants showed the greatest shortfall between 3 and 12 months, making this the age band for maximum probable benefit from focused intervention programmes.

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.

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.

Dietary fiber in weaning cereals: a study of the effect on stool characteristics and absorption of energy, nitrogen, and minerals in healthy infants

We evaluated the effect of increased dietary fiber (DF) content in weaning cereals based on wheat/soy (8.0 and 1.8% DF) and wheat/milk (5.3 and 2.0% DF) in healthy, formula-fed infants 7-17 weeks old. The study had a cross-over design, each infant acting as his or her own control. Stool characteristics and anthropometry were monitored over 4-week periods in groups of 34 (wheat/soy) and 23 (wheat/milk) infants. Absorption of zinc (Zn) and calcium (Ca) was studied by measuring the fecal excretion of stable isotopes during 72 h (70Zn and 42Ca) in a subgroup of the infants consuming wheat/soy cereals. Iron (Fe) bioavailability was evaluated by analysis of the incorporation of 58Fe into erythrocytes 14 days after administration. Fractional absorption (X +/- SD: 8.0 versus 1.8% DF) was 45.3 +/- 27.5 versus 41.2 +/- 19.4% of 70Zn and 63.4 +/- 15.8 versus 64.4 +/- 10.6% of 42Ca. Bioavailability of 58Fe varied between 1.0% and 5.4% (8.0% DF) and from <0.9% to 9.1% (1.8% DF). No significant difference in energy (95.3 +/- 2.0% versus 95.7 +/- 1.2%) or nitrogen (92.6 +/- 2.3% versus 93.0 +/- 1.6%) apparent absorption from the total diet was found during consumption of cereal with 8.0 and 1.8% DF. The intake of cereal decreased with higher DF content in the wheat/soy product: 34 +/- 23 g/d (8.0% DF) versus 42 +/- 23 g/d (1.8% DF), p < 0.01. While consuming the 8.0% DF product, 11 infants were reported to have "gritty stools"; no other differences were observed between different groups in stool characteristics or anthropometry. These results demonstrate no negative effect on the absorption of energy and nutrients with higher dietary fiber intake in primarily formula-fed infants. The impact of increased dietary fiber levels remains unknown in less well-nourished infants.

Effects of different levels of dietary zinc on the gilthead, Sparus aurata during the growing season

Gilthead were fed three diets. Diet A was the control diet, whereas diets B and C were supplemented with 300 and 900 mg Zn/kg, respectively. Fish fed with diet C, at the end of the experiment, showed the lowest weight. Zinc concentrations presented the higher values in gills, liver, and kidney. Muscle and brain had the lower mean values and showed a tight control of zinc levels. These results reinforce the hypothesis that zinc in the CNS should be strictly controlled in order to maintain the functional role of the metal. Significant differences in tissue zinc concentrations were obtained between fish fed different amounts of zinc, the metal concentrations being higher in tissues of fish fed diet C. The tissue decrease of zinc, found at the end of the experiment, may depend on a lower feed consumption or on different zinc requirements during the cold season. These changes, even if not univocal among the three diets, may be associated with the life cycle of fish. Furthermore, copper concentrations were little affected by the different concentrations of zinc in the three diets; liver and kidney presented the highest concentrations; liver showed a significant decrease in copper content at the end of the experiment. We conclude that: zinc concentrations of the diet may affect the gilthead weights and the tissual metal content; and zinc concentrations in the diets, depending on the growth rate, may be varied depending on the season.

Effects of zamic as a means for zinc supplementation in growing children

We investigated the effects of zinc supplementation in case of moderate growth retardation in which GH treatment could not be used. Zamic (ZA, an association containing arginine, L-methionine, and zinc; from Aguettant pharmaceuticals) was compared with arginine aspartate (AA) (5 g) in a crossover randomized trial (6 mo of each treatment at random order over 1 yr). We present preliminary results of 24 children who completed the study (3 girls, 21 boys, age 9-13 yr). Subjects had to be prepubertal, with no GH deficiency diagnosed. In 15 subjects growth velocity was lower than 5 mm/mo: In this case ZA improved growth velocity (rising from 3.105 +/- 0.229 to 5.4 +/- 0.69 mm/mo p < 0.01), whereas the effect of AA was not significant. The increase in growth velocity was higher with ZA (+2.44 +/- 0.657 mm/mo) than AA (+0.438 +/- 0.450 mm/mo) p < 0.05. These results suggest that ZA is more efficient than AA, consistent with the hypothesis that zinc needs are increased in those children in this period of life.

Zinc deficiency in an exclusively breast-fed preterm infant

A formerly premature, exclusively breast-fed infant with severe zinc deficiency syndrome is presented. He showed the characteristic erosive skin changes, including alopecia, as seen in acrodermatitis enteropathica. In addition, he manifested a failure to thrive and irritability. The diagnosis was confirmed by reduced serum levels of zinc (2.3 mumol/l) and alkaline phosphatase (45 U/l). We consider the reduced zinc supply in the breast milk (5.7 mumol/l) as the most likely cause of the disease. Therapy consisted of oral zinc supplements (50 mumol/kg/day) for a period of 30 weeks. Symptoms and laboratory values normalized completely and did not recur on a normal diet.

CONCLUSION

A diet of breast milk can, in rare circumstances, cause insufficient zinc intake resulting in severe zinc deficiency syndrome with characteristic dermatological features. Therapy consists of temporary oral zinc supplementation at a daily dose of 50 mumol/kg.