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 less than 0.06) and repletion (p less than 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.