Function

Iron, as part of hemoglobin, is essential for the transport of oxygen in the blood; it is also part of some of the enzymes needed for cell respiration. Men's bodies have approx. 3.45 g of iron and women approx. 2.45 g, distributed as follows: 60% to 70% in hemoglobin; 10% to 12% in myoglobin and enzymes; and, as ferritin, 29% in men and 10% in women, stored in the liver, spleen, and bone marrow. Iron is stored in the tissues principally as ferritin. It is absorbed from the food in the small intestine and passes, in the blood, to the bone marrow. There it is used in making hemoglobin, which is incorporated into red blood cells. A red cell, after circulating in the blood for approx. 120 days, is destroyed, and its iron is used over again.

Men require from 0.5 to 1.0 mg of iron a day. A woman of menstrual age requires about twice this amount. During pregnancy and lactation from 2 to 4 mg of iron per day is required. Before puberty and after menopause, women require no more iron than men. Because only a fraction of the iron present in food is absorbed, it is necessary to provide from 15 to 30 mg of iron in the diet to be certain that 1 to 4 mg will be absorbed.

In the first few months of life, infants will use up most of their iron stores, and the typical diet or formula may not have sufficient iron to replenish those stores. It is therefore important to add iron-containing foods to an infant's diet by age 6 months.

Manganese, copper, and cobalt are necessary for the proper use of iron. Copper is stored in the body and reused repeatedly.

There are two broad types of dietary iron. About 90% of iron from food is in the form of iron salts and is called nonheme iron, which is poorly absorbed. The other 10% of dietary iron is in the form of heme iron, which is derived primarily from the hemoglobin and myoglobin of meat and is well absorbed. Iron absorption is influenced by other dietary factors. About 50% of iron from breast milk is absorbed but only about 10% of iron in whole cow's milk is absorbed. The reasons for the higher bioavailability of iron in breast milk are unknown. Ascorbic acid, meat, fish, and poultry enhance absorption of nonheme iron. Bran, oxalates, vegetable fiber, tannins in tea, and phosphates inhibit absorption of iron. Orange juice doubles the absorption of iron from the meal and tea decreases it by 75%.

Deficiency Symptoms

Iron deficiency is characterized by anemia, lowered vitality, exertional breathlessness, pale complexion, conjunctival pallor, retarded development, and a decreased amount of hemoglobin in each red cell.

Note

Sometimes a disturbance in iron metabolism occurs, in which an iron-containing pigment, hemosiderin, and hemofuscin are deposited in the tissues, leading to hemochromatosis. Excessive deposition of hemosiderin in the tissues, such as may occur as a result of excessive breakdown of red cells, is called hemosiderosis. See: hemochromatosis

Sources

The following foods provide iron in the diet: almonds, asparagus, bran, beans, Boston brown bread, cauliflower, celery, chard, dandelions, egg yolk, graham bread, kidney, lettuce, liver, oatmeal, oysters, soybeans, and whole wheat. Other good sources are apricots, beets, beef, cabbage, cornmeal, cucumbers, currants, dates, duck, goose, greens, lamb, molasses, mushrooms, oranges, parsnips, peanuts, peas, peppers, potatoes, prunes, radishes, raisins, rhubarb, pineapple, tomatoes, and turnips.