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Current dietary zinc intake has a greater effect on fractional zinc absorption than does longer term zinc consumption in healthy adult men ^1,2,3

¹ From the Program in International and Community Nutrition and the Department of Nutrition, University of California, Davis, CA (JMP, JCK, and KHB); Children's Hospital of Oakland Research Institute, Oakland, CA (CSC, JS, TQN, and JCK); General Clinical Research Center (GCRC), University of California, San Francisco, CA (DD); United States Department of Agriculture, Agricultural Research Service, Cornell University, Ithaca, NY (RW); and the California Department of Public Health, Sanitation and Radiation Laboratory, Richmond, CA (RR)

Background: No studies have examined the independent effects of current and longer-term dietary zinc intakes on zinc absorption.

Objective: We determined the effects of current compared with longer-term zinc intake on fractional zinc absorption (FZA).

Design: We studied 9 men whose usual zinc intakes were >11 mg/d. FZA was measured at baseline, depletion (0.6 mg Zn/d for 1 wk and 4 mg Zn/d for 5 wk), and repletion (11 mg Zn/d for 4 wk with 20 mg supplemental Zn/d for first 7 d). During 2 successive days after each dietary period, subjects consumed either adequate-zinc meals (11 mg Zn/d) with a zinc stable isotope tracer for 1 d, followed by low-zinc meals (4 mg Zn/d) with zinc tracer, or vice versa. Five days after oral dosing, a zinc tracer was infused intravenously. FZA was measured with the use of a modified double isotope tracer ratio method with urine samples collected on days 5–7 and 10–12 of absorption studies.

Results: Plasma and urinary zinc did not vary by dietary period. Mean FZA was greater from low-zinc meals than from adequate-zinc meals (60.9% ± 13.8% compared with 36.1% ± 8.9%; P < 0.0001), whereas mean total absorbed zinc was greater from adequate-zinc meals than from low-zinc meals (3.60 ± 0.91 compared with 2.48 ± 0.56; P < 0.0001), regardless of the longer-term dietary period.

Conclusions: FZA was inversely related to current zinc intake, but there was no detectable effect of longer-term dietary zinc. If longer- term zinc intake does modify FZA, such changes are smaller than those caused by current zinc intake, or they occur only after more severe zinc depletion.