Effects of Vitamin C on Iron Absorption

Jessica Beck, Ohio Northern University, PharmD Candidate 2014
Iron is an essential component of many proteins involved in oxygen transport in the human body and also plays an integral part in the regulation of cell growth and differentiation. The bioavailability of iron depends on several factors, including the form that it takes. Heme iron is the most readily absorbed form of iron and is found in foods such as red meat, shellfish, poultry, and fish. Nonheme iron is less readily absorbed by the body and is found in foods such as fortified cereal, rice, black beans, soybeans, eggs, wheat, and spinach. Although nonheme iron is harder for the body to absorb, it is still an important source of dietary iron. When patients become deficient in iron and diet alone cannot restore iron levels back to normal within a sufficient time frame, iron supplementation with reduced compounds such as ferrous sulfate is indicated. 
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin thought to increase the absorption of nonheme iron. Vitamin C acts as a reducing agent to facilitate iron absorption from the GI tract and to enable its mobilization from storage. The vitamin C and iron combine to form an iron chelate complex, which increases the solubility of iron in the small intestine, resulting in increased uptake across the mucus membranes of the duodenum. For this reason, the vitamin C must be consumed at the same time as the iron in order to be effective. Foods such as broccoli, bell peppers, red cabbage, sweet potatoes, tomatoes, cantaloupe, oranges, mangos, and strawberries are considered excellent sources of vitamin C. Vitamin C can also be taken in oral supplement form. Simultaneous consumption of 25-100 mg of vitamin C has been shown to increase the absorption of nonheme iron by four-fold. However, an excess of 200 mg of vitamin C per 30 mg of elemental iron is required to enhance the absorption of highly available iron salts, such as ferrous sulfate. The amount of iron absorption is considered directly proportionate to the amount of vitamin C taken in. 
In addition, vitamin C is also thought to counteract the effects of dietary phytates and tannins, which are known inhibitors of iron absorption. Phytates, found in grains, legumes, nuts, and rice, can decrease the absorption of iron by up to 50 percent. Tannins are found in wine, chocolate, teas, and coffee. Eating foods containing vitamin C or taking vitamin C supplements along with these foods can make up for their inhibiting effects by chemically reducing iron and preventing the formation of less soluble compounds.
Several clinical studies have shown the ability of vitamin C to increase serum iron, ferritin, and hemoglobin concentrations. Overall, increased vitamin C intake through supplementation or dietary consumption represents an important strategy for improving an individual’s iron status. However, it is important to assess each individual patient’s needs, as supplementation is not always necessary, especially for patients whose diet contains plenty of vitamin C.
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