Many foods, beverages, and supplements have been shown to affect the absorption of iron.110
Foods, beverages and supplements that interfere with iron absorption include
Green tea (Camellia sinensis).111, 112, 113, 114 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.115
Coffee (Coffea arabica, C. robusta).116, 117, 118
Red wine, particularly the polyphenol component (also found in tea).119, 120 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.121, 122, 123
Whole wheat bran, independent of its phytate content, has been shown to inhibit iron absorption.124
Calcium from food and supplements interferes with heme-iron absorption.125, 126
Soy protein.127, 128
Foods and supplements that increase iron absorption include
Although vitamin C increases iron absorption,136, 137, 138, 139 the effect is relatively minor.140
Taking vitamin A with iron helps treat iron deficiency, since vitamin A improves the absorption and/or utilization of iron.141, 142
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.143 Some soy sauces may also enhance iron absorption.144
Alcohol, but not red wine, has been reported to increase the absorption of ferric, but not ferrous, iron.145, 146
Iron has been reported to potentially interfere with manganese absorption. In one trial, women with high iron status had relatively poor absorption of manganese.147 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.148 These interactions suggest that taking multiminerals that include manganese may protect against manganese deficiencies that might otherwise be triggered by taking isolated iron supplements.