How Does Coffee Block The Absorption Of Iron In Humans?

Iron is a metallic mineral that is required for your health. According to Dr. Elson Haas, author of "Staying Healthy with Nutrition," iron is found in every cell in your body, although most of your body's iron is found in hemoglobin, the oxygen-carrying pigment in your red blood cells. Your daily iron requirements are influenced by your age and sex and whether you are pregnant, but everyone needs at least some dietary iron. Certain components in coffee can interfere with your body's absorption of iron.

Heme or Nonheme Iron

The Office of Dietary Supplements reports that the iron in your diet occurs in two forms. The form that your body can absorb most easily is called heme iron. As its name implies, the iron atom in heme iron is surrounded by a hemoglobin-like molecule that protects it from chemical changes that would make it more difficult to absorb across your intestinal lining. Heme iron is found in red meats, poultry and fish. In contrast, nonheme iron is derived from plant sources, and it is somewhat harder for your body to absorb. Most dietary iron -- and that found in most supplements -- is non-heme iron.

Impaired Absorption

The amount of iron you absorb from your food or supplement depends on your body's need for iron -- you absorb iron more efficiently when your body stores are low. Absorption is also related to the proportions of heme and nonheme iron in your diet and other dietary factors that either improve or impair absorption. The Iron Disorders Institute notes a variety of substances that can impair intestinal iron absorption, including anti-ulcer medications, calcium, oxalates, phytates, tannins, certain egg proteins and polyphenols.

Coffee and Iron

At least two substances in coffee interfere with iron absorption. Chlorogenic acid, a polyphenol found in coffee, and coffee-based tannins both bind to iron, forming insoluble compounds that then cannot be absorbed from your intestine. The degree to which coffee interferes with iron absorption depends on the timing of your coffee consumption and how strong your coffee is. The March 1983 issue of "The American Journal of Clinical Nutrition" demonstrated that strong coffee consumed at the time of your meal could reduce iron absorption by more than 90 percent. This interference is far more pronounced with nonheme iron.

Considerations

Dietary recommendations for iron vary from 0.27 mg daily for infants to 33 mg for premenopausal women following a vegetarian diet. According to a review in the May 2000 issue of "The American Journal of Clinical Nutrition," drinking coffee at the time of your meals or up to several hours afterward can interfere with the absorption of dietary iron. Likewise, the benefits of an iron supplement can be largely negated by drinking coffee at or near the time you take your supplement. For optimal iron absorption, do not drink coffee within two hours of consuming your most iron-rich meal of the day or taking your iron supplement.