Iron

Iron, one of the most abundant metals in the universe and one of the most important in the body, is a key component of hemoglobin, a part of red blood cells that carries oxygen to body cells. Cells require oxygen to break down glucose and produce energy. Iron is also part of myoglobin, a muscle protein that stores and carries oxygen that the muscles use to contract. Iron works with many enzymes in energy metabolism and is needed to make amino acids as well as certain hormones and neurotransmitters. Iron also is a part of enzymes found in leukocytes (white blood cells—part of the immune system). About 15 percent of your body's iron is stored for future needs (in the bone marrow, spleen, and liver) and mobilized when dietary intake is inadequate.

• Hemoglobin— A protein in rod blood cells that carries oxygen to the body's cells.
• Myoglobin— A muscle protein that stores and carries oxygen that the muscles will use to contract

About one-third of iron in the American diet comes from beef and enriched breads, rolls, and crackers. Other sources include shellfish, legumes, fortified cereals, green leafy vegetables, and poultry.

Only about 15 percent of dietary iron is absorbed in healthy individuals. The greatest influence on iron absorption is the amount stored in your body. Iron absorption significantly increases when body stores are low. When iron stores are high, absorption decreases to help protect against iron overload. The body also absorbs iron more efficiently when there is a high need for red blood cells, such as during growth spurts or pregnancy or due to blood loss.

The ability of the body to absorb and use iron from different foods varies. The predominant form of iron in animal foods, called heme iron, is absorbed and used twice as readily as iron in plant foods, called nonheme iron. Animal foods also contain some nonheme iron. The presence of vitamin C in a meal increases nonheme iron absorption, as does consuming meat, poultry, and fish. Calcium, substances found in tea and coffee, oxalic acid (in some vegetables such as spinach), and phytic acid (in grain fiber) can decrease the absorption of nonheme iron. Some proteins found in soybeans also inhibit nonheme iron absorption.

• Heme iron— The predominant form of iron in animal foods, it is absorbed and used more readily as iron in plant foods.
• Nonheme iron— A form of iron found in all plant sources of iron and also as part of the iron in animal foot sources.

Iron deficiency is the most common nutritional deficiency. Iron deficiency results in feelings of being tired, irritable, or depressed. If severe enough, it results in iron-deficiency anemia, a condition in which the size and number of red blood cells are reduced. The blood hemoglobin concentration also falls. This condition may result from inadequate intake of iron, inadequate intestinal absorption, excessive blood loss (from heavy menses, ulcers, or types of cancer), and/or increased needs. Women of childbearing age, pregnant women, older infants and toddlers, and teenage girls are at greatest risk of developing iron deficiency anemia because they have the greatest needs. Premenopausal women have higher needs for iron than men because of monthly blood loss during menstruation.

• Iron-deficiency anemia— A condition in which the size and number of red blood cells are reduced; may result from inadequate iron intake or from blood loss; symptoms include fatigue, pallor, and irritability.

Signs of iron-deficiency anemia include feeling tired and weak, decreased work and school performance, slow cognitive and social development during childhood, difficulty maintaining body temperature, and decreased immune function. During pregnancy, iron deficiency is associated with increased risk of premature delivery, giving birth to infants with low birth weight, and maternal complications. Iron supplementation, such as ferrous sulfate pills, authorized by a physician are generally helpful.

Although the body generally avoids absorbing huge amounts of iron, some people can absorb large amounts. The problem with iron is that once it is in the body, it is hard to get rid of. For individuals who can absorb much iron, large doses of iron supplements can damage the liver and do other damage, a condition called iron overload or hemochromatosis. This condition is usually caused by a genetic disorder.

• Iron overload (hemochromatosis)— A common genetic disease in which individuals absorb about twice as much iron from their food and supplements as other people.

It is especially important to keep iron supplements away from children, because they are so toxic they can kill. Consuming 1 to 3 grams of iron can be fatal to children under 6, and lower doses can cause severe symptoms such as vomiting and diarrhea. It is important to keep iron supplements tightly capped and away from children's reach.

Iron in Foods 

Foods	Milligrams Iron
Meat and Poultry
Beef liver, 3 ounces	5.3
Sirloin steak, 3 ounces	2.6
Hamburger, 3 ounces, lean	1.8
Chicken breast, 3 ounces	0.9
Shellfish
Oysters, breaded, fried, 1	3.0
Clams, raw, 3 ounces	2.6
Vegetables
Spinach, 1 cup, frozen, cooked	2.9
Legumes
Great Northern beans, 1 cup	4.9
Black beans, 1 cup	2.9
Tofu, 2-1/2 inch × 2-3/4 inch × 1 inch cube	2.3
Eggs
Egg yolk, 1	0.9
Dried Fruits
Apricots, 1/4 cup	1.5
Raisins, 1/4 cup	0.7
Breads and Cereals
Corn flakes cereal, 1 ounce	1.8
Whole-wheat bread, 1 slice	1.0
White bread, 1 slice	0.7
Source: Nutritive Value of Foods, U.S. Department of Agriculture Home and Garden Bulletin No. 72, 1989.