Comparison of estimates of zinc absorption in humans by using 4 stable isotopic tracer methods and compartmental analysis

Abstract

Adjustment of gastrointestinal absorption is the primary means of maintaining zinc homeostasis; however, a precise, accurate method for measuring zinc absorption in humans has not been identified. The purpose of this study was to compare the estimates of the fraction of dietary zinc absorbed (FZA) by using 4 stable isotopic tracer methods: mass balance (MB) corrected for endogenous secretion, fecal monitoring (FM), deconvolution analysis (DA), and the double isotopic tracer ratio (DITR) method. All 4 methods were applied to a single data set for each of 6 women. FZA was also determined for each subject by using a detailed compartmental model of zinc metabolism, and that value was used as the reference with which the simpler methods were compared. The estimates of FZA (&xmacr; +/- SD) determined by DA (0.27 +/- 0. 08) and the DITR technique in plasma (0.30 +/- 0.10), 24-h urine samples (0.29 +/- 0.09), and spot urine samples (0.291 +/- 0.089) all compared well with the FZA reference value from the compartmental model (0.30 +/- 0.10). The MB and FM methods tended to overestimate FZA compared with the reference value. The determination of FZA by MB or FM is laborious, is sensitive to subject compliance, and may result in an overestimate. DA, although relatively accurate, has the disadvantage of requiring multiple blood drawings over several days. In contrast, the DITR technique applied to a spot urine specimen obtained >/=3 d after tracer administration provides an accurate measure of FZA and is easy to implement; therefore, it is the recommended method for determination of FZA.