Studies on the Bioavailability of Zinc in Man. Effects of the Guatemalan Rural Diet and of the Iron-Fortifying Agent, NaFeEDTA

Abstract

By serial determination of the change in plasma zinc concentration following a standard dose of 110 mg of zinc sulfate heptahydrate, containing 25 mg of elemental zinc, the biological availability of zinc was evaluated in human subjects. Plasma zinc concentration was stable in the fasting state. Following the standard dose of zinc (25 mg) in water, plasma zinc concentration rose above the fasting, baseline levels by 61.0, 68.0, 52.0 and 37.8 µg/dl, respectively, at the first four hourly sampling intervals. Four hours after a standard meal, based on the traditional rural diet of Guatemala and consisting of 120 g of corn tortillas, 120 g of black bean gruel, 40 g of sweet rolls and 250 ml of coffee sweetened with 15 g of sugar, plasma zinc concentration was significantly lower (-18 µg/dl) than the fasting level. Addition of 25 mg of zinc to the black bean gruel in the meal prevented this decline, but did not increase plasma zinc above fasting levels; apparently zinc absorption was inhibited by the meal. Probably, phytates, dietary fiber and calcium are major factors, and coffee is a minor factor in this inhibition. The chelate of iron with ethylenediaminetetraacetate (NaFeEDTA), an iron-fortifying agent proposed for use in Guatemala, at doses of 15 mg, equivalent to that in a cup of coffee sweetened with 15 g of fortified sugar, and at doses of 40 mg, equivalent to that consumed in a day by rural Guatemalans, did not significantly depress zinc uptake. Moreover, no influence of 15 mg of NaFeEDTA beyond that of coffee or food, itself, was detected. High doses of NaFeEDTA, outside of the normal range, impaired zinc absorption, and the EDTA moiety, rather than iron, was responsible. Our data suggest that fortification of sugar with NaFeEDTA at one part per thousand would not influence zinc nutriture, but that the basic Guatemalan diet, itself, impairs zinc nutriture.