The richest sources of heme iron in the diet include lean meat and seafood. Dietary sources of nonheme iron include nuts, beans, vegetables, and fortified grain products. In the United States, about half of dietary iron comes from bread, cereal, and other grain products. Breast milk contains highly bioavailable iron but in amounts that are not sufficient to meet the needs of infants older than 4 to 6 months.

In the United States, Canada, and many other countries, wheat and other flours are fortified with iron. Infant formulas are fortified with 12 mg iron per liter.

Heme iron has higher bioavailability than nonheme iron, and other dietary components have less effect on the bioavailability of heme than nonheme iron. The bioavailability of iron is approximately 14% to 18% from mixed diets that include substantial amounts of meat, seafood, and vitamin C (ascorbic acid, which enhances the bioavailability of nonheme iron) and 5% to 12% from vegetarian diets. In addition to ascorbic acid, meat, poultry, and seafood can enhance nonheme iron absorption, whereas phytate (present in grains and beans) and certain polyphenols in some non-animal foods (such as cereals and legumes) have the opposite effect. Unlike other inhibitors of iron absorption, calcium might reduce the bioavailability of both nonheme and heme iron. However, the effects of enhancers and inhibitors of iron absorption are attenuated by a typical mixed western diet, so they have little effect on most people’s iron status.

Several food sources of iron are listed in Table 2. Some plant-based foods that are good sources of iron, such as spinach, have low iron bioavailability because they contain iron-absorption inhibitors, such as polyphenols.

Table 2: Selected Food Sources of Iron
Food Milligrams
per serving
Percent DV*
Breakfast cereals, fortified with 100% of the DV for iron, 1 serving 18 100
Oysters, eastern, cooked with moist heat, 3 ounces 8 44
White beans, canned, 1 cup 8 44
Chocolate, dark, 45%–69% cacao solids, 3 ounces 7 39
Beef liver, pan fried, 3 ounces 5 28
Lentils, boiled and drained, ½ cup 3 17
Spinach, boiled and drained, ½ cup 3 17
Tofu, firm, ½ cup 3 17
Kidney beans, canned, ½ cup 2 11
Sardines, Atlantic, canned in oil, drained solids with bone, 3 ounces 2 11
Chickpeas, boiled and drained, ½ cup 2 11
Tomatoes, canned, stewed, ½ cup 2 11
Beef, braised bottom round, trimmed to 1/8” fat, 3 ounces 2 11
Potato, baked, flesh and skin, 1 medium potato 2 11
Cashew nuts, oil roasted, 1 ounce (18 nuts) 2 11
Green peas, boiled, ½ cup 1 6
Chicken, roasted, meat and skin, 3 ounces 1 6
Rice, white, long grain, enriched, parboiled, drained, ½ cup 1 6
Bread, whole wheat, 1 slice 1 6
Bread, white, 1 slice 1 6
Raisins, seedless, ¼ cup 1 6
Spaghetti, whole wheat, cooked, 1 cup 1 6
Tuna, light, canned in water, 3 ounces 1 6
Turkey, roasted, breast meat and skin, 3 ounces 1 6
Nuts, pistachio, dry roasted, 1 ounce (49 nuts) 1 6
Broccoli, boiled and drained, ½ cup 1 6
Egg, hard boiled, 1 large 1 6
Rice, brown, long or medium grain, cooked, 1 cup 1 6
Cheese, cheddar, 1.5 ounces 0 0
Cantaloupe, diced, ½ cup 0 0
Mushrooms, white, sliced and stir-fried, ½ cup 0 0
Cheese, cottage, 2% milk fat, ½ cup 0 0
Milk, 1 cup 0 0


* DV = Daily Value. The U.S. Food and Drug Administration (FDA) developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for iron on Nutrition Facts and Supplement Facts labels and used for the values in Table 2 is 18 mg for adults and children age 4 years and older. FDA requires food labels to list iron content. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.

The U.S. Department of Agriculture’s (USDA’s)  lists the nutrient content of many foods and provides a comprehensive list of foods containing iron arranged by nutrient content and by food name.

Dietary supplements

Iron is available in many dietary supplements. Multivitamin/multimineral supplements with iron, especially those designed for women, typically provide 18 mg iron (100% of the DV). Multivitamin/multimineral supplements for men or seniors frequently contain less or no iron. Iron-only supplements usually deliver more than the DV, with many providing 65 mg iron (360% of the DV).

Frequently used forms of iron in supplements include ferrous and ferric iron salts, such as ferrous sulfate, ferrous gluconate, ferric citrate, and ferric sulfate. Because of its higher solubility, ferrous iron in dietary supplements is more bioavailable than ferric iron. High doses of supplemental iron (45 mg/day or more) may cause gastrointestinal side effects, such as nausea and constipation. Other forms of supplemental iron, such as heme iron polypeptides, carbonyl iron, iron amino-acid chelates, and polysaccharide-iron complexes, might have fewer gastrointestinal side effects than ferrous or ferric salts.

The different forms of iron in supplements contain varying amounts of elemental iron. For example, ferrous fumarate is 33% elemental iron by weight, whereas ferrous sulfate is 20% and ferrous gluconate is 12% elemental iron. Fortunately, elemental iron is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of iron supplied by various forms of iron supplements.

Approximately 14% to 18% of Americans use a supplement containing iron. Rates of use of supplements containing iron vary by age and gender, ranging from 6% of children aged 12 to 19 years to 60% of women who are lactating and 72% of pregnant women.

Calcium might interfere with the absorption of iron, although this effect has not been definitively established. For this reason, some experts suggest that people take individual calcium and iron supplements at different times of the day.

Monday, July 20, 2020 - 09:49