Validation of an Extrinsic Iron Label in Monitoring Absorption of Nonheme Food Iron in Normal and Iron-deficient Rats

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Abstract
Absorption of an extrinsic iron label as a means of monitoring absorption of nonheme food iron was assessed in iron-deficient and iron-replete female rats utilizing a dual isotope technique that allowed simultaneous administration of an intrinsic iron label (corn, soybean, or wheat biosynthetically labeled) and an extrinsic iron label. The method was assessed under diverse conditions including changes in quantity of test food, inclusion of other foods, addition of chelates, and use of normal and iron-deficient animals. This diversity produced a wide range in iron absorption, yet, in each case, absorption of the extrinsically labeled iron closely paralleled absorption of the intrinsically labeled iron. The ratio of the absorption of extrinsic to intrinsic iron was consistent in all 16 studies and for all 113 animals, averaging 1.14. The data mirrors prior human studies, suggesting that the extrinsic iron label enters the soluble nonheme iron pool and can serve to estimate the extent of iron absorption from that pool. Whereas the extrinsic iron label technique cannot assess absorption of insoluble iron as iron phosphates or large particulate iron, it appropriately permits study of factors that enhance or inhibit absorption of nonheme food iron, particularly in animals of varying iron status.