Iron absorption from the whole diet in men: how effective is the regulation of iron absorption?

Iron absorption from the whole diet, which contained a highly bioavailable form of iron, was measured for 5 d in 31 health men, including 12 blood donors. Nonheme iron in all meals was labeled with an extrinsic, inorganic radioiron tracer added in amounts to ensure uniform specific activity in all meals. Heme iron was labeled similarly by using hemoglobin biosynthetically labeled with another radioiron tracer. There was a good inverse relation between total absorption and concentration of serum ferritin up to approximately 60 micrograms/L. In subjects with serum ferritin > 60 micrograms/L there was no relation to iron absorption. At this serum ferritin concentration, absorption decreased to a level just sufficient to cover basal iron losses, implying that at a serum ferritin concentration > or = 60 micrograms/L no further accumulation of iron stores will occur by dietary iron absorption. The findings thus suggest that in normal subjects there is no risk of developing iron overload by iron absorption from the diet even if the diet is fortified. Similar findings were made previously in two studies in women, both of which indicated an effective control of absorption. At the same serum ferritin concentration the absorption per kilogram body weight was the same in men and women served identical diets with a high iron bioavailability. These new observations strongly suggest that translation of serum ferritin concentration into amounts of stored iron should be made with caution and that in subjects with high serum ferritin concentrations, other causes than increased iron stores should be considered. There was effective control of both heme- and nonheme-iron absorption but their relations to iron status were different.