IRON ABSORPTION. IV. THE ABSORPTION OF HEMOGLOBIN IRON*

TLDR

Iron absorption from hemoglobin, hemin, and ferritin has been compared to ferrous salts in healthy and iron‑deficient subjects. Hemoglobin iron is absorbed as well or better than ferrous salts in normal subjects, shows reduced responsiveness to iron depletion, is unaffected by food or phytate, and is absorbed as a porphyrin complex with delayed plasma appearance, indicating that the current iron‑absorption model based on salts does not apply to all food iron.

Abstract

The absorption of radioiron in rabbit hemoglobin, hemin, and ferritin has been compared to that of ferrous salt in healthy volunteers and in subjects with iron-deficiency anemia. At a dosage level of 5 mg elemental iron, hemoglobin iron was as well or better absorbed than ferrous salts in the normal subject. Absorption of hemoglobin iron increased less, however, in the iron-depleted or iron-deficient subject. In contrast to the absorption of ferrous salts, that of hemoglobin iron was not decreased by food or by phytate nor increased by ascorbic acid. The absorption of hemin iron was also not decreased by food. Iron absorbed from hemoglobin appeared in the plasma later than that from ferrous salts, but was found to be similarly dialyzable at acid pH with EDTA. These findings suggest that iron in heme complexes is absorbed as a porphyrin complex without conversion to the free ionized form. It is further apparent that there is less effective mucosal regulation of absorption of iron in this form. Finally, the present hypothesis of iron absorption based on the behavior of iron salts is not adequate for all types of food iron.