Iron Sources & Supplements

Food Sources

The amount of iron in food (or supplements) that is absorbed and used by the body is influenced by the iron nutritional status of the individual and whether or not the iron is in the form of heme. Because it is absorbed by a different mechanism than nonheme iron, heme iron is more readily absorbed and its absorption is less affected by other dietary factors. Individuals who are anemic or iron deficient absorb a larger percentage of the iron they consume (especially nonheme iron) than individuals who are not anemic and have sufficient iron stores.

Heme iron: Heme iron comes mainly from hemoglobin and myoglobin in meat, poultry, and fish. Although heme iron accounts for only 10-15% of the iron found in the diet, it may provide up to one third of total absorbed dietary iron. The absorption of heme iron is less influenced by other dietary factors than that of nonheme iron.

Nonheme iron: Plants, dairy products, meat, and iron salts added to foods and supplements are all sources of nonheme iron. The absorption of nonheme iron is strongly influenced by enhancers and inhibitors present in the same meal.

Enhancers of nonheme iron absortion

Vitamin C (ascorbic acid): Vitamin C strongly enhances the absorption of nonheme iron by reducing dietary ferric iron (Fe³⁺) to ferrous iron (Fe²⁺) and forming an absorbable iron-ascorbic acid complex.

Other organic acids: Citric, malic, tartaric, and lactic acids have some enhancing effects on nonheme iron absorption.

Meat, fish, and poultry: Aside from providing highly absorbable heme iron, meat, fish, and poultry also enhance nonheme iron absorption. The mechanism for this enhancement of nonheme iron absortion is not clear.

Inhibitors of nonheme iron absorption

Phytic acid (phytate): Phytic acid is present in legumes, grains, and rice and is an inhibitor of nonheme iron absorption. Small amounts of phytic acid (5 to 10 mg) can reduce nonheme iron absorption by 50%. The absorption of iron from legumes, such as soybeans, black beans, lentils, mung beans, and split peas, has been shown to be as low as 2%.

Polyphenols: Polyphenols, found in some fruits, vegetables, coffee, tea, wines, and spices, can markedly inhibit the absorption of nonheme iron. This effect is reduced by the presence of vitamin C.

Soy protein: Soy protein, such as that found in tofu, has an inhibitory effect on iron absorption that is independent of its phytic acid content.

National surveys in the U.S. indicate that the average dietary iron intake is 16-18 mg/day in men, 12 mg/day in pre- and postmenopausal women, and about 15 mg/day in pregnant women. Thus, the majority of premenopausal and pregnant women in the U.S. consume less than the RDA for iron and many men consume more than the RDA. In the U.S., most grain products are fortified with iron. The iron content of some relatively iron-rich foods is listed in milligrams (mg) in the table below. For more information on the nutrient content of foods you eat frequently, search the USDA food composition database.

Food	Serving	Iron content (mg)
Beef	3 ounces*, cooked	2.31
Chicken, dark meat	3 ounces, cooked	1.13
Oysters	6 medium	5.04
Shrimp	8 large, cooked	1.36
Tuna, light	3 ounces, canned	1.30
Black-strap molasses	1 tablespoon	3.50
Raisin bran cereal	1 cup, dry	5.00
Raisins, seedless	1 small box (1.5 ounces)	0.89
Prune juice	6 fluid ounces	2.27
Prunes, dried	~ 5 prunes (1.5 ounces)	1.06
Potato, with skin	1 medium potato, baked	2.75
Kidney beans	1/2 cup, cooked	2.60
Lentils	1/2 cup, cooked	3.30
Tofu, firm	1/4 block (~1/2 cup)	6.22
Cashew nuts	1 ounce	1.70

*A three-ounce serving of meat is about the size of a deck of cards.

Supplements

Iron supplements are indicated for the prevention and treatment of iron deficiency. Individuals who are not at risk of iron deficiency (e.g., adult men and postmenopausal women) should not take iron supplements without an appropriate medical evaluation for iron deficiency. A number of iron supplements are available, and different forms provide different proportions of elemental iron. Ferrous sulfate (heptahydrate) is 22% elemental iron; ferrous sulfate (monohydrate) is 33% elemental iron; ferrous gluconate is 12% elemental iron; ferrous fumarate is 33% elemental iron. If not stated otherwise, all of the iron doses discussed in this presentation represent elemental iron.

See also: