HOMEOSTASIS OF ZINC IN MARGINAL HUMAN ZINC-DEFICIENCY - ROLE OF ABSORPTION AND ENDOGENOUS EXCRETION OF ZINC

Although biochemical and immunologic aspects of mild or marginal human zinc deficiency have been well characterized, there is a paucity of d ata regarding the effects of prolonged marginal zinc deficiency on zin c homeostasis. It appears that human beings are able to maintain zinc homeostasis by increasing efficiency of zinc absorption and decreasing endogenous excretion of zinc when they are subjected to short-term di etary zinc restriction. However, a mild deficiency of zinc in human be ings under usual circumstances is an outcome of chronic exposure to di ets low in zinc lasting for many months and years. Therefore, it is im portant to determine whether or not the adapted zinc homeostasis durin g the short duration of dietary zinc deprivation is also maintained du ring a prolonged period of dietary zinc restriction. We assessed the e fficiency of zinc absorption as well as endogenous zinc excretion duri ng a 6-month period of dietary zinc restriction (63.1 mumol/day) in hu man volunteers by using a stable zinc (Zn-70). Prolonged marginal zinc deficiency did not impair the functional role of endogenous zinc excr etion in zinc homeostasis, but efficiency of zinc absorption was not s ustained and decreased in the majority of our volunteers when the zinc -restricted diet was continued for 6 months. Such altered mechanisms o f zinc homeostasis suggest that chronic human zinc deficiency warrants reassessment of dietary zinc requirement to preserve normal zinc stat us in the subsets of population that are vulnerable to zinc deficiency .