Facts About Iron

Part 1: What is iron, what affects its absorption, and how much do you need?

Iron is an essential mineral and an important component of proteins involved in oxygen transport and metabolism(1,2). Almost two-thirds of the iron in your body is found in hemoglobin, the protein in red blood cells that carries oxygen to your body’s tissues. Smaller amounts of iron are found in myoglobin, a protein that helps supply oxygen to muscle, and in enzymes that assist biochemical reactions in cells. About 15 percent of your body’s iron is stored for future needs and mobilized when dietary intake is inadequate. The remainder is in your body’s tissues as part of proteins that help your body function. Adult men and post-menopausal women lose very little iron except through bleeding. Women with heavy monthly periods can lose a significant amount of iron. Your body usually maintains normal iron status by controlling the amount of iron absorbed from food(1,3).

There are two forms of dietary iron: heme and nonheme. Iron in meat, fish, and poultry is found in a chemical structure known as heme. Heme iron is absorbed very efficiently by your body (1,3-4). Iron in plants such as lentils and beans is arranged in a different chemical structure called nonheme iron. Nonheme iron is not as well absorbed as heme iron(1,3-4). Flours, cereals, and grain products that are enriched or fortified with iron are good dietary sources of nonheme iron (5). The addition of iron to infant formulas, cereals, and grain products has been credited with improving the iron status of millions of infants, children, and women. The tables of selected food sources of heme and nonheme iron suggest many dietary sources of iron.

Iron absorption refers to the amount of dietary iron that your body obtains from food. Healthy adults absorb about 15% of the iron in their diet, but your actual absorption is influenced by your body’s iron stores, the type of iron in the diet, and by other dietary factors that either help or hinder iron absorption(1,3,6-9).

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(1,3).

Absorption of heme iron is very efficient and not significantly affected by the composition of your diet(1). Only 1% to 7% of the nonheme iron in vegetable staples such as rice, maize, black beans, soybeans and wheat is absorbed when consumed as a single food (3). However, dietary factors can significantly improve nonheme iron absorption (1,3, 6-9). Meat proteins and vitamin C will improve the absorption of nonheme iron (1,10). Diets that include a minimum of 5 servings of fruits and vegetables daily, as recommended by the Food Guide Pyramid, should provide plenty of vitamin C to boost nonheme iron absorption. Calcium, polyphenols and tannins found in tea, and phytates, which are a component of plant foods such as legumes, rice and grains, can decrease the absorption of nonheme iron(1,11-15). Some proteins found in soybeans also inhibit nonheme iron absorption (1,16). Most healthy individuals can maintain normal iron sores when the diet provides a wide variety of foods as suggested by the Food Guide Pyramid. It is most important to include foods that enhance nonheme iron absorption when total daily iron intake does not meet the RDA, when iron losses are exceptionally high, or when no heme iron is usually consumed.

The Recommended Dietary Allowance (RDA) is the daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each life-stage and gender group(1). The 2001 RDAs for iron (in milligrams) for infants ages 7 to 12 months, children and adults(1) are:

2001 RDAs for Iron

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