Zinc tolerance tests in zinc deficient and zinc supplemented diets

Seven men consumed a low-zinc (3.3 mg/day) diet for 8 wk, followed by zinc-repletion (+15 mg/day) for 12 days. Zinc tolerance tests (50 mg) were administered initially and following depletion and repletion periods. Plasma zinc after 2 h in the zinc tolerance test was marginally higher after both the depletion (p < 0.06) and repletion (p < 0.001) periods as compared to the initial test. No changes were seen in parotid zinc tolerance tests or fasting levels of zinc in plasma or parotid saliva. In a subsequent study, zinc tolerance tests were given to normal subjects before and after 12 days of zinc supplementation (15 mg/day). Again, zinc levels in plasma were increased following zinc supplementation at the 2nd h post-zinc dose, but levels in saliva did not change. The elevation of plasma zinc curves with both zinc deficiency and supplementation suggests that this test is not a reliable indicator of zinc status.