Also See:
Coffee Inhibits Iron Absorption
Iron’s Dangers
Int J Vitam Nutr Res Suppl. 1989;30:103-8.
The role of vitamin C in iron absorption.
Hallberg L, Brune M, Rossander L.
Iron requirements remain the same despite the current lower energy requirement. This means that more iron must be absorbed per unit energy. A higher bioavailability of the dietary iron can be achieved by increasing the content of food components enhancing iron absorption (ascorbic acid, meat/fish) or by decreasing the content of inhibitors (e.g., phytates, tannins). The latter is not feasible considering the recent and reasonable trend toward increasing the intake of dietary fibre. The key role of ascorbic acid for the absorption of dietary nonheme iron is generally accepted. The reasons for its action are twofold: (1) the prevention of the formation of insoluble and unabsorbable iron compounds and (2) the reduction of ferric to ferrous iron, which seems to be a requirement for the uptake of iron into the mucosal cells.
Fed Proc. 1983 Apr;42(6):1716-20.
An overview of current information on bioavailability of dietary iron to humans.
Morris ER.
Bioavailability factors can greatly modify the absorption of dietary iron consumed in different meals by an individual. A greater percentage is generally absorbed of heme iron from animal tissues than of nonheme iron of either animal or plant food. The amount of meat in a meal is the only bioavailability factor known to influence absorption of heme iron. Absorption of iron from the exchangeable nonheme iron pool of a meal is influenced by both enhancing and inhibiting substances or factors. Ascorbic acid, meat, fish, and poultry enhance absorption of nonheme iron, and meals may be classified according to relative bioavailability depending on the content of meat, fish, poultry, and/or ascorbic acid. Some low-molecular-weight organic acids may also increase the bioavailability of nonheme iron. Synthetic metal-chelating agents added to foods and the beverages tea and coffee will inhibit absorption of nonheme iron in a concentration-dependent manner. Wheat bran, soy products, cow’s milk, and egg tend to decrease bioavailability of nonheme iron when included in a meal. However, the effect of compounds thought to be responsible for the inhibition in purified form (phytate, fiber, phosphoproteins) is dependent on chemical form and concentration. In some foods there may be as yet unidentified inhibitors or interaction between compounds to inhibit absorption of nonheme iron. Currently available information permits estimation of relative bioavailable iron in a meal.
Ann N Y Acad Sci. 1980;355:32-44.
Interaction of vitamin C and iron.
Lynch SR, Cook JD.
Food iron is absorbed by the intestinal mucosa from two separate pools of heme and nonheme iron. Heme iron, derived from hemoglobin and myoglobin, is well absorbed and relatively little affected by other foods eaten in the same meal. On the other hand, the absorption of nonheme iron, the major dietary pool, is greatly influenced by meal composition. Ascorbic acid is a powerful enhancer of nonheme iron absorption and can reverse the inhibiting effect of such substances as tea and calcium/phosphate. Its influence may be less pronounced in meals of high iron availability–those containing meat, fish, or poultry. The enhancement of iron absorption from vegetable meals is directly proportional to the quantity of ascorbic acid present. The absorption of soluble inorganic iron added to a meal increases in parallel with the absorption of nonheme iron, but ascorbic acid has a much smaller effect on insoluble iron compounds, such as ferric oxide or ferric hydroxide, which are common food contaminants. Ascorbic acid facilitates iron absorption by forming a chelate with ferric iron at acid pH that remains soluble at the alkaline pH of the duodenum. High cost and instability during food storage are the major obstacles to using ascorbic acid in programs designed to combat nutritional iron deficiency anemia.
