The typical daily diet of most Americans contains approximately 10 to 20 mg of iron. (3) Sources of dietary iron include heme iron from meats and nonheme iron from whole grains and vegetables. Many processed foods, such as breakfast cereal, are fortified with iron.
However, the normal individual absorbs only 5% to 15% of dietary iron, or about 1 to 2 mg daily. Females may absorb slightly more iron than males as they require more iron to replace that lost through menstruation and to meet the increased need for iron in pregnancy.
Absorption of iron occurs through the mucosal cells (enterocytes) in the duodenum (proximal small intestine). Dietary iron that is not absorbed is excreted in the feces. Intestinal absorption provides the means for regulating the amount of iron in the body, and the amount absorbed is mediated by the level of storage iron.
The amount of iron absorbed is normally low because iron is well conserved within the body. Heme iron from senescent (aged) erythrocytes is cycled back into the iron pool and reused for incorporation into developing erythrocytes. Furthermore, iron is normally lost from the body only in very small amounts, primarily through desquamation of mucosal cells in the gastrointestinal tract and losses through body secretions, including urine, sweat and feces. Therefore, under normal conditions, very little dietary iron needs to be absorbed to maintain iron homeostasis.(4)