Iron
Last Updated on Sunday, 28 February 2010 20:56
Iron, one of the most abundant metals on Earth, is essential to most life forms and to normal human physiology. Iron is an integral part of many proteins and enzymes that maintain good health. In humans, iron is an essential component of proteins involved in oxygen transport, and it is also essential for the regulation of cell growth and differentiation.
A deficiency of iron limits oxygen delivery to cells, resulting in fatigue, poor work performance, and decreased immunity. On the other hand, excess amounts of iron can result in toxicity and even death.
Almost two-thirds of iron in the body is found in hemoglobin, the protein in red blood cells that carries oxygen to tissues. Smaller amounts of iron are found in myoglobin, a protein that helps supply oxygen to muscle, and in enzymes that assist biochemical reactions. Iron is also found in proteins that store iron for future needs and that transport iron in blood. Iron stores are regulated by intestinal iron absorption.
Recommended Intake
The Food & Nutrition Board at the Institute of Medicine of the National Academies established recommended dietary allowances for iron for children and adults. They are listed in below in milligrams (mg) per day.
| Age | Males (mg/day) | Females (mg/day) | Pregnancy (mg/day) | Lactation (mg/day) |
|---|---|---|---|---|
| 0 to 6 months | 0.27* | 0.27* | ||
| 7 to 12 months | 11 | 11 | N/A | N/A |
| 1 to 3 years | 7 | 7 | N/A | N/A |
| 4 to 8 years | 10 | 10 | N/A | N/A |
| 9 to 13 years | 8 | 8 | N/A | N/A |
| 14 to 18 years | 11 | 15 | 27 | 10 |
| 19 to 50 years | 8 | 18 | 27 | 9 |
| 51+ years | 8 | 8 | N/A | N/A |
* Iron in human breast milk is well absorbed by infants. It is estimated that infants can use greater than 50 percent of the iron in breast milk as compared to less than 12 percent of the iron in infant formula. The amount of iron in cow's milk is low, and infants poorly absorb it.
Sources of Heme Iron
| Food | Milligrams per serving | Percent Daily Value * |
|---|---|---|
| Chicken liver, cooked, 3½ ounces | 12.8 | 70 |
| Oysters, breaded and fried, 6 pieces | 4.5 | 25 |
| Beef, chuck, lean only, braised, 3 ounces | 3.2 | 20 |
| Clams, breaded, fried, ¾ cup | 3.0 | 15 |
| Beef, tenderloin, roasted, 3 ounces | 3.0 | 15 |
| Turkey, dark meat, roasted, 3½ ounces | 2.3 | 10 |
| Beef, eye of round, roasted, 3 ounces | 2.2 | 10 |
| Turkey, light meat, roasted, 3½ ounces | 1.6 | 8 |
| Chicken, leg, meat only, roasted, 3½ ounces | 1.3 | 6 |
| Tuna, fresh bluefin, cooked, dry heat, 3 ounces | 1.1 | 6 |
| Chicken, breast, roasted, 3 ounces | 1.1 | 6 |
| Halibut, cooked, dry heat, 3 ounces | 0.9 | 6 |
| Crab, blue crab, cooked, moist heat, 3 ounces | 0.8 | 4 |
| Pork, loin, broiled, 3 ounces | 0.8 | 4 |
| Tuna, white, canned in water, 3 ounces | 0.8 | 4 |
| Shrimp, mixed species, cooked, moist heat, 4 large | 0.7 | 4 |
Sources of Nonheme Iron
| Food | Milligrams per serving | Percent Daily Value* |
|---|---|---|
| Ready-to-eat cereal, 100% iron fortified, ¾ cup | 18.0 | 100 |
| Oatmeal, instant, fortified, prepared with water, 1 cup | 10.0 | 60 |
| Soybeans, mature, boiled, 1 cup | 8.8 | 50 |
| Lentils, boiled, 1 cup | 6.6 | 35 |
| Beans, kidney, mature, boiled, 1 cup | 5.2 | 25 |
| Beans, lima, large, mature, boiled, 1 cup | 4.5 | 25 |
| Beans, navy, mature, boiled, 1 cup | 4.5 | 25 |
| Ready-to-eat cereal, 25% iron fortified, ¾ cup | 4.5 | 25 |
| Beans, black, mature, boiled, 1 cup | 3.6 | 20 |
| Beans, pinto, mature, boiled, 1 cup | 3.6 | 20 |
| Molasses, blackstrap, 1 tablespoon | 3.5 | 20 |
| Tofu, raw, firm, ½ cup | 3.4 | 20 |
| Spinach, boiled, drained, ½ cup | 3.2 | 20 |
| Spinach, canned, drained solids ½ cup | 2.5 | 10 |
| Black-eyed peas (cowpeas), boiled, 1 cup | 1.8 | 10 |
| Spinach, frozen, chopped, boiled ½ cup | 1.9 | 10 |
| Grits, white, enriched, quick, prepared with water, 1 cup | 1.5 | 8 |
| Raisins, seedless, packed, ½ cup | 1.5 | 8 |
| Whole wheat bread, 1 slice | 0.9 | 6 |
| White bread, enriched, 1 slice | 0.9 | 6 |
*Daily Values were developed by the U.S. Food and Drug Administration to help consumers compare the nutrient contents among products within the context of a total daily diet. The daily value for iron is 18 milligrams. Foods providing 20 percent or more of the daily value are considered to be a high source of a nutrient, but food providing lower percentages of the daily value also contribute to a healthful diet.
