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Human Nutrition and Metabolism
Research Communication

Heme-Iron Absorption Is Saturable by Heme-Iron Dose in Women

Institute of Nutrition and Food Technology (INTA) of University of Chile, Santiago, Chile

²To whom correspondence should be addressed. E-mail: fpizarro{at}uec.inta.uchile.cl.

In developed countries where meat is an important constituent of the diet, much of the dietary iron is in the heme-iron form as hemoglobin and myoglobin. Heme-iron is absorbed more efficiently than inorganic iron by the human intestine. Thus, it is important to know how the dose of heme-iron affects iron absorption. The purpose of this study was to establish the dose-effect of heme-iron on the percentage and absolute amount of iron absorbed. Twenty-seven healthy women (28- to 50-y-old) were selected to participate in two iron absorption studies. Through the use of iron isotopes (⁵⁹Fe and ⁵⁵Fe), the studies were performed to characterize the dose–response curve of non–heme-iron absorption (ferrous sulfate), and to establish the dose–response curve of heme-iron absorption (hemoglobin). The labeled hemoglobin was prepared by use of red blood cells from rabbits. The geometric means (±1 SEM range) of non-heme iron absorbed were 0.2 (0.2–0.3), 1.2 (1.0–1.5), 6.7 (5.7–8.0) and 13.0 (11.5–14.6) mg of iron for doses of 0.5, 5, 50 and 100 mg of iron as ferrous sulfate, respectively; and 0.1 (0.1–0.2), 0.4 (0.3–0.4), 2.2 (2.0–2.4) and 2.2 (1.7–3.0) mg of iron for doses of 0.5, 3, 15 and 30 mg of heme-iron as hemoglobin, respectively. The fitted curves for heme and non-heme iron differed (P < 0.04). These results strongly suggest that the heme-iron absorption pathway is saturable.

KEY WORDS: • heme-iron absorption • iron bioavailability • iron fortification • iron status

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