An average American adult diet consisting of a variety of common foods bought at a grocery store or eaten in a restaurant or institution would normally contain about 15 milligrams of iron per day. Because of the poor absorption of iron this may be a rather marginal amount. Therefore, to insure adequate iron intake, most people should supplement their diet. Most of the iron enters the blood stream directly and not via the lymphatics. The precise mechanism by which this absorption takes place across the mucosal cells is not known.
Evidence indicates that absorption is regulated to some extent by physiological demand.
The important factors may be iron stores, hypoxia, erythropoietic activity and level of unsaturated iron-binding protein. Thus, persons who are iron-deficient tend to absorb iron more efficiently and in greater quantities than do normal subjects. This phenomenon has been demonstrated with medicinal ferrous sulfate and with food tagged with radioactive Fe 59 . There are several other factors which affect iron absorption. A recent report suggest that egg yolk, despite its relatively large amount of iron, inhibits the absorption of iron.