A secondary analysis by researchers at the University of Southern California looked at 643 men in the Aspirin/Folate Polyp Prevention (AFPP) Study who took 1,000 mcg of folic acid daily as a supplement or a placebo for 10 years. Lead researcher Dr. Jane Figueredo found the folic acid supplement group had nearly three times the risk of developing prostate cancer compared to control subjects who took a placebo. The results of this study appeared in the March 10, 2009 online issue of the Journal of the National Cancer Institute.

While aspirin use in the AFPP study was associated with a lower risk of developing polyps, those taking 1,000 mcg of folic acid actually had somewhat more polyps develop. These results were somewhat surprising because previous studies have shown that low levels of dietary folate are associated with an increased risk of colon and several other types of cancer including prostate cancer. The AFPP study ran from 1994 to 2006. After 10 years of follow-up an estimated 9.7% of the men taking the folic acid supplement developed prostate cancer compared to only 3.3% of those taking the placebo.The B-vitamin folate comes in several forms. The synthetic form is folic acid and it is believed to be more efficiently absorbed than naturally occurring folate found in foods such as beans, whole grains, fruits and vegetables. Folic acid is now added to enriched grain products mainly to reduce the risk of spina bifida. In addition many men started taking folic acid supplements often in doses of 1,000 mcg to 5,000 mcg as a way to lower elevated homocysteine (Hcy) levels in their blood. While folic acid supplements do lower Hcy and elevated Hcy is associated with more cardiovascular disease (CVD), recent clinical trials with folic acid supplements failed to reduce CVD events. Unfortunately, there are many men who are still taking high doses of folic acid for a variety of reasons.Given the dubious efficacy of folic acid supplements to lower CVD risk or slow the development of precancerous colon polyps and now with data linking at least high dose folic acid with prostate cancer, the time has come to discourage men from taking high doses of folic acid.Prostate cancer remains the number one cancer killer among non-smoking U.S. men. About 220,000 U.S. men will be diagnosed with prostate cancer and about 28,000 men are expected to die from it. A lack of sunshine and vitamin D are increasingly linked to a higher risk of developing prostate cancer. The consumption of more red meat and processed meats is also linked to increased risk of developing prostate cancer as is a diet high in dairy products and calcium. Being overweight or obese and having insulin resistance also appears to promote the growth of prostate cancer. We may now have to add high doses of at least the synthetic form of the B-vitamin folate (folic acid) to the list of suspected promoters of prostate cancer.  Bottom Line:The results of this study certainly should not be interpreted to mean avoiding foods high in folate would help prevent prostate cancer. Indeed, while the evidence is not consistent men whose intake of folate rich foods such as beans, fruits, vegetables, and whole grains is high appear to have a reduced risk of prostate cancer as well as a lower risk of several other cancers and CVD. Indeed, even in this recent study higher levels of natural folate in the blood showed a trend toward a lower risk of prostate cancer. This is not the case with the synthetic form of folate. It seems clear that taking high doses of folic acid as a supplement makes no sense for men.  By James J. Kenney, PhD, RD, FACN.