Zinc and infant nutrition

https://doi.org/10.1016/j.abb.2016.06.011Get rights and content

Highlights

  • Zinc is critical for infant growth and development.

  • Zinc nutrition depends on zinc bioavailability.

  • Zinc deficiency is a major global health issue that affects young children.

  • Alterations in zinc transporters can cause zinc-deficient breast milk.

Abstract

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.

Introduction

Infancy is a critical phase of life that requires adequate nutrition to sustain growth and development. Pioneers in the field of zinc biology identified many years ago that at birth, a neonate has only small pools of metabolically available zinc, as evidenced by early onset growth failure in conditions of zinc restriction, despite the presence of normal tissue zinc levels [1]. Thus establishing the zinc requirements for infants has been of great importance. This chapter discusses the importance of zinc nutrition, sources of dietary zinc and its bioavailability, requirements for mineral supplementation, risk factors for zinc deficiency, the effects of zinc deficiency and its contribution to the global burden of disease. The consequences of mutations and epigenetic changes to key zinc transporters provide insights into the cellular mechanisms regulating zinc homeostasis that are of particular importance to the health and development of infants and young children.

Section snippets

Essentiality of zinc

Zinc has many diverse roles in biological processes. At the cellular and molecular level, zinc is required for the structural and catalytic function of hundreds of enzymes that regulate the major metabolic pathways of the body [2]. As a structural component of transcription factors [3], zinc has a key role in regulation of gene expression and is involved in signal transduction and neuronal transmission [4], [5]. Numerous cellular processes require zinc including cell proliferation,

Nutrition and body zinc status

The concept of body zinc status is based on the notion of acquisition of zinc that is sufficient for optimal biological processes. Body zinc status may be a consequence of dietary zinc intake, phytate consumption, gastrointestinal health, rate of zinc excretion and reabsorption, and other factors, many of which are not clear [13]. As there are numerous biological functions of zinc, many measures of zinc status have been considered, including zinc levels blood, urine, hair, feces, sweat, and

Dietary zinc requirements of infants

Dietary requirements for essential nutrients including zinc provide estimates of whether intakes are adequate for optimal body function. The RDA (recommended dietary allowance) is the daily intake amount of a nutrient that is considered to be sufficient to meet the requirements of 97.5% of healthy individuals over the age of 6 months. RDAs for zinc vary between different countries and range from 1.5 to 2 mg/day for 0–6 months of age, 3–8 mg/day for 7–12 months of age and 4–9 mg/day for 1–3 year

Zinc in human breast milk and infant formulas

Neonates are born with a substantial storage of zinc (25% of total body zinc) bound primarily to metallothioneins in the liver, that accumulate in the last trimester of gestation [26], [27], [28]. These hepatic zinc reserves are progressively reduced until they reach a constant level at approximately 4 months of age [28], [29]. However, unlike iron and copper, the major source of zinc in the neonatal period is breast milk [29]. The zinc concentration in human milk is highest in colostrum

Zinc bioavailability in milk

Stable isotope studies and zinc loading tests show that human milk has a greater zinc bioavailability than cow’s milk and infant formulas [40], [41]. Zinc absorption in healthy adults was on average 41% from human milk, 28% from cow’s milk, 31% from casein-based formula and only 14% from soy based formula [40]. A higher fractional absorption of zinc from human milk (54%) was found in infants [50]. An important factor in zinc bioavailability is the whey-to-casein ratio as zinc is more

Dietary factors influencing zinc nutrition in infants

Micronutrient interactions can affect zinc bioavailability and absorption. This can be through competition of transport processes or through zinc chelation. Iron supplements may interfere with zinc absorption [63], [64]. Cadmium can inhibit zinc absorption while some amino acids including histidine and methionine increase zinc absortion [65]. Dietary zinc bioavailability is influenced by many food constituents including phytate, a plant ligand of inositol phosphate that is present in cereals

Vegetarianism

Meat and seafood are major sources of dietary zinc, while the zinc in plant-based diets containing folate, fibre and phytochemicals, is less available [68]. Although grains, nuts and seeds can provide amounts of zinc similar to those found in animal tissues, adult populations with vegetarian diets have been found to have low zinc intakes [69], [70], [71], [72] and in some cases reduced serum zinc levels [73]. Other studies on adults show no effects of vegetarian diets on serum zinc [70], [72],

Effect of maternal zinc status on infant health

Although 82% of all pregnant women worldwide are estimated to be zinc deficient [76], zinc levels in human milk were found to be unrelated to maternal zinc status as measured by maternal plasma zinc levels [77], and the zinc status of the lactating mother does not influence transfer of zinc into milk [78], [79], [80], [81], [82], [83], [84], [85]. Additionally, the majority of studies show no correlation between maternal age, parity or smoking habits on zinc levels in milk [78], [86], [87], [88]

Zinc deficiency in infants

Zinc deficiency is a prevalent condition in countries with poor nourishment and particularly affects infants and young children. Due to the numerous roles of zinc in cell growth, differentiation and function and the lack of body stores, the infant is particularly susceptible to the adverse effects of zinc deficiency. Zinc deficiency accounts for the deaths of over half a million infants and children under 5 years of age, per year [13]. The WHO estimates that 800,000 deaths per year are due to

Zinc supplementation

Preterm babies represent approximately about 12% of births in USA, and have a higher risk of micronutrient deficiency than term babies [113]. Zinc fortification of this group has been recommended [114]. Preterm babies are recommended to have zinc supplements ranging from 200 to 500 μg/kg/day for infants born between 27 and 40 weeks gestation [22]. Very low birthweight premature infants, less than 1.5 kg at birth are recommended to have supplementation of 10 mg Zn/day beginning at week 1 until

Genetic conditions in infants that are associated with zinc deficiency

The most frequently occurring form of zinc deficiency is due to nutritional insufficiency. Rarer forms of zinc deficiency that are inherited may be found in exclusively breast-fed babies, who present with symptoms characteristic of nutritional zinc deficiency, including dermatitis, diarrhoea, alopecia, loss of appetite, impaired immune function and neuropsychiatric changes [109], [123]. This type of zinc deficiency (transient neonatal zinc deficiency) is caused by reduced levels of zinc in the

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