Zinc absorption as a function of the dose of zinc sulfate in aqueous solution.

Background: Zinc supplements are used extensively in medicine and research and for public health purposes in the prevention and treatment of zinc deficiency. However, little is known about the efficiency of zinc utilization after different doses.
Objective: The objective was to determine the relation between dose of aqueous zinc and absorbed zinc (AZ) in healthy adults.
Design: Eight healthy adults (3 men and 5 women) aged 33.8 +/- 9.8 y (x +/- SD) received 3 pairs of zinc doses (2 and 5, 10 and 15, and 20 and 30 mg) in random order in 3 phases (1 pair per phase). There was a 3-wk washout between phases. Aqueous zinc sulfate labeled with 70Zn or 68Zn was orally administered in the postabsorptive state on days 1 and 6, respectively; intravenous 67Zn was administered 1 h after the first oral zinc dose. Two urine samples were collected daily from days 3 to 15; zinc isotopic ratios were determined by inductively coupled plasma mass spectrometry. Fractional absorption of zinc (FAZ) was determined by dual-isotope-tracer ratio; AZ was calculated by multiplying FAZ by dose.
Results: Mean (+/-SD) AZ values at doses of 2.2, 5.2, 10.4, 15.2, 20.3, and 30.1 mg ingested Zn were 1.6 +/- 0.4, 3.5 +/- 1.3, 7.4 +/- 1.0, 9.5 +/- 2.2, 11.0 +/- 4.4, and 11.2 +/- 2.1 mg, respectively. A saturable dose-response model, the Hill equation, was selected to model the relation of AZ to ingested zinc. Parameter estimation by nonlinear regression predicted a maximum zinc absorption of 13 mg for larger doses.
Conclusions: Increases in aqueous zinc doses >20 mg result in relatively small and progressively diminishing increases in AZ postabsorptively in healthy adults.