Iron in ferritin or in salts (ferrous sulfate) is equally bioavailable in nonanemic women

Abstract

Recent studies in humans suggest that ferritin iron in soybeans has high bioavailability. However, direct evidence for this is lacking because the soybeans were intrinsically labeled; thus, iron bound to other ligands, such as phytate, was also labeled. The objectives of the study were to evaluate the absorption of iron from extrinsically labeled, purified ferritin (horse spleen) reconstituted with either high-phosphate iron mineral (plant-type) or low-phosphate iron mineral (animal-type) and to compare it with iron absorption from ferrous sulfate. Nonanemic, healthy young women were fed a standard breakfast meal supplemented with (59)Fe-labeled ferritin or ferrous sulfate, in randomized order. Fifteen subjects received ferritin with the low-phosphate iron mineral, and 15 subjects received ferritin with the high-phosphate iron mineral. Iron absorption was measured in a whole-body counter after 14 and 28 d and by red blood cell incorporation after 28 d. There was no significant difference in iron absorption between ferritin and ferrous sulfate: low-phosphate iron mineral ferritin (x +/- SD: 21.4 +/- 14.7%) compared with ferrous sulfate (21.9 +/- 14.6%), or high-phosphate iron mineral ferritin (22.2 +/- 19.2%) compared with ferrous sulfate (16.7 +/- 7.1%). Results obtained by using whole-body retention of iron and red blood cell incorporation differed with the type of iron, which suggests that pathways for iron uptake and utilization differed for the 2 forms. Iron is equally well absorbed from ferritin and ferrous sulfate independent of the phosphate content of the ferritin iron mineral. Thus, dietary ferritin iron is likely to be a good source of iron.