Absorption of stable70 Zn in healthy young men in relation to zinc intake

Zinc absorption was measured in two groups of four healthy young men using the method of stable tracer isotope neutron activation analysis. All absorption measurements were made using a test dose of ZnCl2 in subjects who participated in an overnight fast and also in subjects from whom food was withheld for 5 h after ingestion of tracer. In one group of experimental subjects, dietary zinc intake was held constant (approximately 15 mg/day), and three different test doses of the tracer were administered at weekly intervals. Fractional absorption was 81% from a 4.52-mg dose, 67% from a 6.47 mg dose and 61% for a 24.52-mg dose. In the other group of subjects, dietary zinc was reduced from approximately 15 mg to less than 2 mg/day. This was accompanied by a significant increase in fractional zinc absorption of a fixed tracer zinc dose (1.19 mg), from 81 to 92%. This increase, which occurred within 6 days, was also measurable when the tracer zinc dose was increased to 4.76 mg. These data indicate that there is a significant effect of the dose level of stable zinc isotope on its fractional absorption. They also demonstrate that a restriction in dietary zinc intake results in a prompt increase in the absorption of a fixed pulse dose of zinc in healthy young men.