Despite the many jokes about doctors and their love of golf, golf clubs aren’t the only “irons” physicians talk about. Although it’s in the headlines less often than protein, trans fat, or calcium, iron is more than just the metal in a golf club — it’s also an important part of your diet, and a lack of iron can cause some serious problems.
Iron is an essential mineral that is needed for the formation of red blood cells, hemoglobin (the protein in red blood cells that carries oxygen), and myoglobin (the protein that carries oxygen in muscle). In addition to carrying oxygen, iron is involved in energy metabolism, collagen formation, immune system function, and the production of neurotransmitters such as serotonin and dopamine. Approximately two-thirds of the iron in our bodies is found in hemoglobin, with smaller amounts found in myoglobin, some catalytic molecules (enzymes), and in storage molecules such as ferritin (a protein that stores iron and releases it when the blood has too little of it).
Despite iron’s many roles, the total amount of iron in the body only adds up to roughly one teaspoon. About 15% of our body’s iron is stored for future needs or as a backup for when dietary intake is insufficient. Our bodies obtain iron from the food that we eat (or supplements), and on average, we lose about 1 milligram of iron each day (a very small amount) through intestinal blood loss (and some small amounts lost through sweat and urine), although premenopausal women lose more iron than others from blood lost through menstruation.
Food sources of iron
The iron we consume from foods comes in two forms, heme and nonheme. Heme iron is found in meat, poultry, fish, and eggs. Nonheme iron is found in foods of plant origin, including dark green, leafy vegetables, nuts, seeds, legumes, iron-enriched grains, and dried fruits. Certain grain foods such as pasta, white rice, and many types of bread are enriched with iron by food manufacturers, because naturally occurring iron is often lost during food processing. And many cereals are fortified with 100% of the Recommended Dietary Allowance (RDA) for iron. (Click here for a list of dietary sources of heme and nonheme iron.)
The body absorbs anywhere from 15% to 35% of heme iron, compared to 1% to 7% of nonheme iron. However, an individual’s absorption of dietary iron depends on several factors. If iron stores are low, for example, the body compensates by increasing iron absorption from food. Likewise, if iron stores are high, absorption will normally decrease. Iron absorption is increased during a child’s growth spurt, and also during pregnancy, due to the extra demand for this mineral.
Absorption of heme iron is usually unaffected by the rest of your diet. However, some food ingredients can hinder iron absorption from foods containing nonheme iron, including caffeine and calcium. Tannins and polyphenols, which are found in tea, and phytates, found in many plant foods such as legumes and grains, also decrease the absorption of nonheme iron.
Meat proteins and vitamin C, on the other hand, increase iron absorption from foods with nonheme iron. Eating a food rich in vitamin C, such as an orange or a tomato, with a meal can increase absorption of nonheme iron sixfold. Following the Food Guide Pyramid’s recommendation of five servings of fruits and vegetables a day can help to maximize iron absorption.
Soy foods can also be a source of iron; however, like other legumes, soybeans naturally contain phytates, which reduce iron absorption. Fermentation is thought to break down phytates, so fermented soy products such as miso or tempeh provide more iron than nonfermented soy products such as tofu or soy flour.
Another way to increase iron in your diet is to cook foods in iron pots and pans. Small amounts of iron from the cookware leach into foods cooked in them.