What is folic acid?

Quick Answer
The synthetic, oxidized form of the B vitamin folate that is used in commercial vitamin supplements and food fortification.
Expert Answers
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Cancers treated or prevented: Colorectal cancer, breast cancer

Delivery routes: Natural dietary sources, fortified foods, oral supplements

How this substance works: Folate is an essential cofactor in the de novo synthesis of purines and thymidylate and therefore plays a role in DNA synthesis, replication, stability, and repair. Evidence suggests that folate deficiency can lead to DNA damage and is associated with macrocytic anemia, neural tube defects, and cancer. In 1998, the US Food and Drug Administration (FDA) began requiring the fortification of all flour and cereal grains with folic acid. These products are thus a major source of folic acid in the US population. Large epidemiological studies that followed subjects for many years have found that higher dietary intake of folate and folic acid supplementation decreased the risk of colon and breast cancer. A possible explanation for its protective effect is that folate prevents DNA damage that may lead to the development of cancer.

Side effects: Research results on the benefits of folate in preventing cancer are inconsistent. Despite population studies showing positive effects of higher folate intake, studies in animals and humans also have shown that folic acid supplementation increased the risk of breast cancer and the development of colon polyps. These mixed results suggest that folate has a dual role in the development of cancer. In normal tissues, folate appears to suppress the development of cancer, presumably by preventing mutations. Once early lesions or tumors have developed, however, folate appears to promote their progression in colorectal and breast cancers. In these cases, folic acid may provide a source of nucleotides for rapidly proliferating tissues, including tumors. Indeed, antifolate drugs are sometimes used in the treatment of cancer. Thus, the timing, dose, and form of folate appear to be critical in whether this substance prevents or actually promotes certain types of cancers. For these reasons, the National Institutes of Health (NIH) do not currently recommend folic acid supplements to reduce the risk of cancer.


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