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 average 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.
Iron is absorbed through the duodenum's mucosal cells (enterocytes) (proximal small intestine). Dietary iron that is not absorbed is excreted in the feces. Intestinal absorption regulates the amount of iron in the body, and the level of storage iron mediates the amount absorbed.
The amount of iron absorbed is ordinarily 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 typically lost from the body only in tiny amounts, primarily through desquamation of mucosal cells in the gastrointestinal tract and losses through body secretions, including urine, sweat, and feces. Therefore, very little dietary iron must be absorbed under normal conditions to maintain iron homeostasis.4
