Absorption of Iron from the Diet

The dietary requirement for iron depends on the amount and composition of the food, the amount of iron lost from the body, and variations in physiological state such as growth, onset of menses, and pregnancy. The average North American diet contains about 6 mg of iron per 1000 calories and supplies about 10-15 mg/d. Of that ingested, 8-10% (1-1.5 mg/d) is absorbed. Thus, dietary factors that affect absorption are more important than the iron content of the diet and may be more important for correction of iron deficiency than addition of iron to the diet. 

Senescent red blood cells are catabolized by the macrophages, the salvaged iron is temporarily stored, and made available via transferrin for erythron and for hemoglobin synthesis. 

Ferrous iron is absorbed principally from the mature enterocytes lining the absorptive villi of the duodenum. The amount of iron absorption by these enterocytes is 

At normal levels of iron intake, absorption requires uptake from the intestinal lumen by the mucosa and transfer from the mucosa to the portal blood. Both events are inversely affected by the state of body iron stores. In iron deficiency states, nonferrous metals such as cobalt and manganese, which have an ionic radius similar to that of iron and form octahedral complexes with six-coordinate covalent bonds, also are absorbed at an increased rate. Oral administration of a large dose of iron reduces (or temporarily inhibits) the absorption of a second dose of iron by the absorptive enterocytes even in the presence of systemic iron deficiency. The mechanism of mucosal block, which resists acquiring additional iron by the en-teroeytes with high amounts of intracellular iron, is not yet understood. It probably involves set points established in the enterocytes for iron recently consumed in the diet (dietary regulator). 

Iron absorption also is affected by erythropoiesis. When erythropoiesis is accelerated by bleeding, hemolysis, or hypoxia, iron absorption is increased. Conversely, 

---

Absorption of iron from the diet is an inefficient process which may be enhanced or inhibited by the iron status of the individual consuming the diet, the form of iron in individual foods, and interactions between foods consumed in a single meal (1-4) Because of this, estimates of iron bioavailability obtained from iron absorption measurements are necessary in... 

---