Does Zinc Absorption Reflect Zinc Status?
Unlike iron, zinc absorption is influenced by dietary zinc intake, not zinc status. As dietary zinc increases, the total amount of absorbed zinc increases while the percent absorbed declines. The gastrointestinal tract maintains whole-body zinc homeostasis by adjusting endogenous zinc losses to the amount absorbed. At intakes below about 9 mg/day, zinc absorption occurs primarily by a saturable (carrier) process involving ZIP4, ZnT1, and other transporters. There is no evidence that past zinc intakes, or status, influences zinc absorption. Instead, current zinc intake is the chief determinant of zinc absorption. Supplemental zinc taken with water in the post-absorptive state initially is absorbed more efficiently than food zinc, but absorption efficiency declines within 24 hours presumably due to down-regulation of the zinc transporters. More research is needed to understand the effect of physiological state on zinc absorption.