Many foods, beverages, and supplements have been shown to affect the absorption of iron.108
Foods, beverages and supplements that interfere with iron absorption include
Green tea (Camellia sinensis).109, 110, 111, 112 This effect may be desirable for people with iron overload diseases, such as hemochromatosis. The inhibitory effect of green tea on iron absorption was 26% in one study.113
Coffee (Coffea arabica, C. robusta).114, 115, 116
Red wine, particularly the polyphenol component (also found in tea).117, 118 Since wine is also a dietary source of iron, it is not clear whether drinking red wine would lead to a deficiency of iron.
Phytate (phytic acid), found in unleavened wheat products such as matzoh, pita, and some rye crackers; in wheat germ, oats, nuts, cacao powder, vanilla extract, beans, and many other foods, and in IP-6 supplements.119, 120, 121
Whole wheat bran, independent of its phytate content, has been shown to inhibit iron absorption.122
Calcium from food and supplements interferes with heme-iron absorption.123, 124
Soy protein.125, 126
Foods and supplements that increase iron absorption include
Although vitamin C increases iron absorption,134, 135, 136, 137 the effect is relatively minor.138
Taking vitamin A with iron helps treat iron deficiency, since vitamin A improves the absorption and/or utilization of iron.139, 140
Although soy protein has been shown to decrease iron absorption (see above), certain soy-containing foods (e.g. tofu, miso, tempeh) have significantly improved iron absorption.141 Some soy sauces may also enhance iron absorption.142
Alcohol, but not red wine, has been reported to increase the absorption of ferric, but not ferrous, iron.143, 144
Iron has been reported to potentially interfere with manganese absorption. In one trial, women with high iron status had relatively poor absorption of manganese.145 In another trial studying manganese/iron interactions in women, increased intake of "non-heme iron"--the kind of iron found in most supplements--decreased manganese status.146 These interactions suggest that taking multiminerals that include manganese may protect against manganese deficiencies that might otherwise be triggered by taking isolated iron supplements.