Losses are greater in menstruating women because of blood loss. Humans typically lose only small amounts of iron in urine, feces, the gastrointestinal tract, and skin. Transferrin is the main protein in blood that binds to iron and transports it throughout the body. Much of the remaining iron is stored in the form of ferritin or hemosiderin (a degradation product of ferritin) in the liver, spleen, and bone marrow or is located in myoglobin in muscle tissue. Most of the 3 to 4 grams of elemental iron in adults is in hemoglobin. Heme iron, which is formed when iron combines with protoporphyrin IX, contributes about 10% to 15% of total iron intakes in western populations. Plants and iron-fortified foods contain nonheme iron only, whereas meat, seafood, and poultry contain both heme and nonheme iron. ĭietary iron has two main forms: heme and nonheme. Iron is also necessary for physical growth, neurological development, cellular functioning, and synthesis of some hormones. As a component of myoglobin, another protein that provides oxygen, iron supports muscle metabolism and healthy connective tissue. Iron is an essential component of hemoglobin, an erythrocyte (red blood cell) protein that transfers oxygen from the lungs to the tissues. Iron is a mineral that is naturally present in many foods, added to some food products, and available as a dietary supplement. For a general overview of Iron, see our consumer fact sheet on Iron. This is a fact sheet intended for health professionals.
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