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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

An Irradiated Electrolytic Iron Fortificant Is Poorly Absorbed by Humans and Is Less Responsive than FeSO₄ to the Enhancing Effect of Ascorbic Acid^1–3,

U.S. Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND

^* To whom correspondence should be addressed. E-mail: jhunt{at}gfhnrc.ars.usda.gov.

Despite extensive use, information on the bioavailability of elemental iron powders to humans, as influenced by dose and other dietary constituents, is limited. Three experiments were conducted to assess the absorption of electrolytic iron powder relative to FeSO₄, as affected by iron dose and by ascorbic or phytic acid. Iron absorption by 56 volunteers was measured from a farina cereal breakfast radiolabeled with ⁵⁹FeSO₄ or an electrolytic ⁵⁵Fe powder irradiated by neutron activation. Absorption was determined from whole-body counting (⁵⁹Fe) and blood isotope incorporation 2 wk later. Absorption of iron from the irradiated electrolytic powder was 5–15% that of FeSO₄. Ascorbic acid (160 mg) enhanced iron absorption from FeSO₄ by almost 4-fold but only doubled absorption from electrolytic iron (P for interaction < 0.01). Phytic acid from wheat bran inhibited iron absorption from FeSO₄ and electrolytic iron by 73 and 50%, respectively (P for interaction, NS). Compared with 3 mg, a 20-mg dose reduced fractional absorption from FeSO₄, but not electrolytic iron (P for interaction < 0.0001). Despite a much higher bioavailability (50% relative to FeSO₄) of this same electrolytic iron when tested previously in a pig model, the bioavailability of the irradiated electrolytic iron was poor in humans. The diminished influence of ascorbic acid on the absorption of less soluble iron sources such as elemental iron powders may be an important consideration when choosing iron fortificants.