Hemoglobin (Hb) contains about 70% of the body iron, and storage iron accounts for most of the remainder. One gram of Hb contains 3.4 mg of iron, and 1 ml of packed red blood cells (RBCs) contains about 1 mg of iron. Iron intake averages about 10 mg/day, of which about 10% is absorbed. Iron loss averages about 1 mg/day in men and nonmenstruating women and about 2 mg/day in menstruating women. There is an additional iron requirement for pregnant and lactating women.

Most body iron originates from dietary iron in the ferric state, which is converted to the ferrous state after ingestion and absorbed predominantly in the duodenum and jejunum. Iron circulates in the blood coupled to a beta globulin, transferrin. Bone marrow RBC precursors use a portion of the available iron; about 60% of the remainder is stored within reticulum cells in bone marrow, liver, and spleen as ferritin and about 40% as hemosiderin. Iron from ongoing RBC death and hemoglobin breakdown is the primary source of iron storage material.

Approximately 50% more oral iron is absorbed if taken 45-60 minutes before food ingestion than if taken with food. Meat inhibits absorption less than dairy products or foods with high fiber content. Coffee and tea also inhibit absorption, whereas vitamin C (given with iron) enhances absorption. Iron in human milk is absorbed much more readily than that in cow’s milk.