Zinc supplementation reduces fractional zinc absorption in young and elderly Korean women

Background: Adjustments in zinc losses and absorption are thought to maintain zinc homeostasis with changes in intake, but the capacity to make these adjustments appears to be affected by aging. Zinc status of the individual may also influence adjustments in fractional zinc absorption. Objective: The purpose of this study was to compare the effects of changes in zinc status due to zinc supplementation on fractional zinc absorption in young and elderly Korean women. Design: Zinc status and absorption were measured initially in 15 young (20-24 yr) and 15 elderly women (64-75 yr) confined to a metabolic unit and consuming a typical Korean diet. Upon discharge from the unit the women were supplemented with 22 mg zinc/d for 28 days. On d 20, the women returned to the unit for measurement of zinc status and absorption. Fractional zinc absorption (FZA) was estimated from the same typical Korean breakfast at both time points using the dual isotopic tracer method. Zinc stable isotopic ratios were measured in urine samples collected for 3 days following isotope administration. Results: Plasma and urinary zinc concentrations increased significantly with zinc supplementation in the young but not the elderly women. FZA decreased following zinc supplementation in the young women from 22 to 8% (p < 0.0001) and in the elderly women from 19 to 10% (p < 0.0001). The decline in young women was greater than that in elderly women (p < 0.05). Conclusions: Both young and elderly women reduced their efficiency of zinc absorption with zinc supplementation. But, plasma and urinary zinc concentrations did not increase in the elderly following zinc supplementation suggesting that age altered the use of the additional zinc.