AN IRRADIATED ELECTROLYTIC IRON FORTIFICANT IS POORLY ABSORBED BY HUMAN SUBJECTS AND IS LESS RESPONSIVE THAN FeSO4 TO THE ENHANCING EFFECT OF ASCORBIC ACID

Authors: SWAIN, JAMES - CASE WESTERN RESERVE UNIV; JOHNSON, LUANN - UNIVERSITY NORTH DAKOTA; Hunt, Janet

Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2006
Publication Date: 8/1/2006
Citation: Swain, J.H., Johnson, L.K., Hunt, J.R. 2006. An irradiated electrolytic iron fortificant is poorly absorbed by human subjects and is less responsive than FeSO4 to the enhancing effect of ascorbic acid. Journal of Nutrition. 136:2167-2174.

Interpretive Summary: Elemental iron powders are small particles of metallic iron that have been useful for food fortification because they are less chemically reactive than more soluble forms of iron such as ferrous sulphate. This lower reactivity causes fewer problems with food discoloration, flavour impairment, and rancidity that reduces shelf life. However, this lower reactivity also reduces our ability to absorb the iron from these sources. We measured human absorption of electrolytic iron, an elemental iron, after neutron activation treatment to produce a readily detectable iron isotope. The iron was poorly absorbed, probably in part because of this treatment. When orange juice with extra ascorbic acid (vitamin C) was served with a hot cereal, iron absorption was improved by 5 times if the cereal was fortified with ferrous sulphate, but only 2 times if fortified with the electrolytic iron. Phytic acid from wheat bran impaired the absorption of both forms of iron. The degree of enhancement of iron absorption by ascorbic acid depends on the form of iron used for fortification.

Technical 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 acids. 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 5 times from FeSO4 vs. 2 times from electrolytic iron (p< 0.01 for interaction). Phytic acid from wheat bran inhibited iron absorption from FeSO4 and electrolytic iron by 73 and 50%, respectively (NS for interaction). Compared to 3 mg, a 20 mg dose reduced fractional absorption from FeSO4, but not electrolytic iron (p< 0.0001 for interaction). Despite a much higher bioavailability (50% relative to FeSO4) of this same electrolytic iron when tested in a pig model (Zinn et al., 1999), the irradiation process likely reduced the bioavailability of the electrolytic iron to 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.