Zinc is an essential nutrient for man, and deficiency states are increasingly being recognized. In infants, dietary requirements for zinc are not well defined, in part because the metabolism of zinc is poorly understood. Also, the availability of zinc from milks, formulas and other foods consumed by infants is not defined well, and the mechanisms by which infants remain in positive zinc balance despite variation in level and source of dietary zinc are largely unknown. In recent years methodological advances have enabled the use of stable (non-radioactive) isotopes as tracers, which has greatly expanded the ability to study the metabolism of zinc and of factors that influence its availability. We have successfully performed studies of zinc metabolism in infants and propose a series of further studies designed to advance and refine our understanding of zinc metabolism in infants. We are using inductively-coupled plasma mass spectrometry (ICP/MS) with a newly developed advanced direct injection nebulizer.
In Specific Aim 1 we propose to refine and simplify the methodology of isotopic tracer studies in infants. This will include a technique for the quantitative collection of stools in infants living at home. This will for the first time make it possible to study the availability of zinc in breast-fed infants.
In Specific Aim 2 we propose non-invasive mechanistic studies designed to explore the effect of varying doses of zinc and of mild zinc deprivation on percent absorption of zinc. We will also determine endogenous excretion of zinc using a technique that has only recently become feasible due to improved analytical sensitivity.
In Specific Aim 3 we will explore the effect of a number of dietary conditions (i.e., breast vs formula) and dietary components (e.g., fiber) on the availability of zinc. These studies will greatly expand our understanding of zinc metabolism in infancy. Specifically, they will define what mechanisms infants use in order to maintain positive zinc balance in the face of varying dietary conditions.
