Researchers affiliated with the Aspirin/Folate Polyp Prevention Study have reported that supplementation with folic acid significantly increases the risk of prostate cancer. The details of this study were reported in the March 18, 2009 issue of the Journal of the National Cancer Institute.[1]

The role of micronutrients in relationship to cancer incidence has become a major focus among researchers. Some dietary choices have been shown to reduce the risk of developing certain types of cancers; however, newer research has also shown exogenous vitamins do not lower the incidence of cancer and in some instances they may increase cancer risks. Thus, there is evolving evidence that exogenous vitamin supplementation is no substitute for micronutrients in food.

The Aspirin/Folate Polyp Prevention Study was a placebo-controlled, randomized trial of aspirin and folic acid supplementation for the prevention of colorectal adenomas. The study included 643 men who were randomly assigned to placebo or supplementation with folic acid. The men completed food frequency questionnaires (FFQ) and also provided nonfasting blood samples for the measurement of circulating levels of folate and other B vitamins. The men were followed for a median of seven years.

The results of this study indicated that the estimated probability of being diagnosed with prostate cancer was 9.7% for the men in the folic acid group compared with 3.3% in the placebo group. Interestingly, both an increased baseline dietary folate intake and a high baseline level of circulating folate in the placebo group was associated with a decreased incidence in prostate cancer. These researchers concluded that daily supplementation with 1 mg of folic acid was associated with an increased risk of prostate cancer; however, they acknowledged that supplementation may have different effects from dietary intake.

Comments: Vitamin supplementation has little or no effect on the incidence of cancer. However, this is one of the few studies to show direct harm of vitamin supplementation by increasing cancer risk.

Reference:

[1] Figueiredo JC, Grau MV, Haile RW, et al. Folic acid and risk of prostate cancer: Results from a randomized clinical trial. Journal of the National Cancer Institute. 2009; 101: 432-435.