The present study is designed in three sequential steps. Study I evaluates an additional tool to measure zinc absorption. In this method, we will determine whether 24-hour urine zinc is a feasible alternative to the AUC which is obtained from the zinc tolerance curve and whether it can provide additional useful data. Study II is designed to evaluate the effect of gastric acidity on absorption of two zinc salts, the acetate and the oxide. In Study III, absorption in elderly subjects, one group with normal gastric acidity, and one with achlorhydria, will be compared. Absorption of both zinc acetate and zinc oxide will be measured. In this way, the inter-relationships among the effects of age, gastric acidity, and zinc salt will be established.