Basic Iron Metabolism

Most of the iron within the body is found in hemoglobin within erythrocytes (about 1800 mg of iron). Iron is stored in macrophages (and to a lesser extent in hepatocytes), which represents the storage pool of iron (about 1600 mg of iron). Small amounts of iron are found in myoglobin and in plasma (bound to transferrin) (see image to the right and below). Iron is conserved within the body. The typical adult human body contains about 3000-4000 mg of iron. Only about 1 mg of iron is lost from the body per day (through blood loss or sloughed mucosal epithelial cells) and must be replaced through the diet. The majority of iron required by the body is acquired by recycling iron from senescent red cells.

Iron metabolism is essential for maintaining health and for the production of erythrocytes, or red blood cells. The intestines extract iron from iron rich foods, which is then stored in the body’s cells as the iron compound ferritin.

Too little ferritin leads to anemia, a condition characterized by insufficient levels of red blood cells or hemoglobin. Excessive ferritin leads to an organ-damaging condition known as iron overload.

Red Blood Cells And Ferritin

Iron metabolism is vital to the formation and proper function of red blood cells. Erythrocytes transport oxygen from the lungs to cells throughout the body. To perform this task, red blood cells require ferritin. Ferritin is stored in the red blood cells’ hemoglobin, where it aids in the binding of oxygen molecules.

Iron Metabolism And Recycled Ferritin

The human body excels at iron metabolism, iron regulation and iron storage. The body’s iron regulation processes are so efficient that only a tiny percent of the body’s iron content relies on daily intestinal iron metabolism.

The total iron content in the average adult male is four grams. Only one to two milligrams of the daily iron requirement comes from the metabolism of iron rich foods. Most of the body’s iron content comes from recycled ferritin.

As cells die and are reabsorbed into the body, iron regulation processes redirect ferritin released from dead cells—particularly red blood cells—to the bone marrow. In the bone marrow, recycled iron is made available to growing erythrocytes.

Iron Metabolism And Iron Excretion

The body’s complex system of iron regulation and ferritin recycling ensures that as little iron is excreted as possible. On average, an adult male loses only 0.9 milligrams a day through the intestines, skin cell exfoliation, sweat and urine. Bleeding can also deplete iron reserves.

Women lose more iron than men because of menstrual bleeding and the high iron demands of pregnancy and lactation. Ferritin lost due to menstrual bleeding adds 0.4 milligrams to a woman’s daily iron loss, so women lose 1.3 milligrams for every 0.9 milligrams of iron lost by men. Iron loss due to pregnancy adds yet another four milligrams to this total.

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