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Folic Acid Supplementation May Increase Cancer Risk


In a study published in the November 18th issue of the Journal of the American Medical Association, heart patients in Norway had a 21% increased risk of cancer when they took large doses of folic acid and vitamin B12 over patients who did not supplement the vitamins.

Dr. Marta Ebbing of Norway’s Haukeland University Hospital and colleagues analyzed data from two studies that included almost 7,000 patients with ischemic heart disease treated with B vitamin supplements for an average of three and a half years between 1998 and 2005. The combinations inclued Vitamins B6, B12, and folic acid.

The original intent of the study was to determine if taking B vitamins improved cardiovascular outcomes. Both folic acid and B12 help break down the amino acid homocysteine in the body. High levels of homocysteine is thought to be a risk factor for heart disease and stroke.

The patients were followed for an average of three years after the study ended, during which time 10% of the patients who took the supplements were diagnosed with cancer versus 8.4% of those who did not. 75% of the cancer-related deaths were due to lung cancer.

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Folic acid helps the body grow new cells. Researchers felt that consumption of high doses of folic acid over a span of more than three years may add to the growth of cancers. This has lead to questions regarding the advantages of fortifying foods with folic acid.

The United States fortifies flour and grain products to decrease the incidence of neural tube defects in pregnancy. Because Norway does not fortify its food products with folic acid, researchers felt this was a good population to study the effects of controlled supplementation. The amount of supplementation given to the patient in the Norway study was significantly higher than what most people in the United States receive from food fortification.

The study is not the first to suggest that folic acid may increase a person’s risk of cancer. A study in March 2009 suggested that folic acid supplements raise the risk of prostate cancer, and a study from April 2009 found an increased risk of colon cancer. Animal studies have suggested that folic acid enhance the growth of abnormal tissue in the colon, though the results were inconsistent.

A confounding factor of the study was smoking. About 70% of the patients in the study were current or former smokers, including 94% of those who developed lung cancer. “The real headline of this study should be that smoking increases the risk of lung cancer,” said Andrew Shao, VP for Scientific and Regulatory Affairs with the Council for Responsible Nutrition (CRN). Shao goes on to say that the fact that lung cancer rates have also dropped since mandatory fortification began suggest that the B vitamins do not promote lung cancer.

The study authors acknowledged that the study lacked information on family history of cancer and the environmental exposure to tobacco.

Dr. Bettina Drake of the Alvin J. Siteman Cancer Center in St. Louis offered this statement in an accompanying editorial in the JAMA issue: “While the results by Ebbing and colleagues provide some short-term data that is important in helping us understand the complexities in the association between folic acid and cancer risk, this report does not nullify the vast potential long-term benefits that folic acid fortification may have on population health.”