An Irradiated Electrolytic Iron Fortificant Is Poorly Absorbed by Humans and Is Less Responsive than FeSO4 to the Enhancing Effect of Ascorbic Acid1–3

Abstract

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.