A new study warns that men who take daily folic acid supplements are at an increased risk of developing prostate cancer.
According to researchers at the University of Southern California (USC), men who consume a daily folic acid supplement of 1 mg daily are more than twice the risk of prostate cancer.
The finding came from a secondary analysis of the Aspirin/Folate Polyp Prevention Study (AFPP), a placebo-controlled randomized trial to determine the impact of aspirin and folic acid on colon polyps in men and women who were at high risk for the disease.
Folic acid (folate) is a B vitamin found in many vegetables, beans, fruits and whole grains. While evidence of its ability to reduce neural tube defects in infants while taken by the mother before or during pregnancy has been well documented, its effects on other conditions are unclear.
"We know that adequate folate levels are important in the prevention of several cancer types, cardiovascular and neurological diseases," says lead author Jane Figueiredo, Ph.D., assistant professor of preventive medicine at the Keck School of Medicine of USC.
"However, little has been known about its role in prostate cancer. Our objective was to investigate the relationship between folic acid supplements and dietary folate and risk of prostate cancer," the expert added.
The study was conducted between 1994 and 2006 and found that aspirin reduced the risk of colon polyps while folic acid had a negative effect and increased the risk of advanced and multiple polyps. The first analysis did not address the impact of folic acid supplements on prostate cancer risk.
In the secondary analysis, researchers looked at prostate cancer incidence among 643 men who were randomly assigned to 1 mg daily folic acid supplements or placebo in the study and who enrolled in an extended follow-up study.
The estimated prostate cancer risk was 9.7 percent at 10 years in men assigned to folate, compared with 3.3 percent in men assigned to placebo.
By contrast, dietary folate intake and plasma folate showed a trend toward reduced risk of prostate cancer, although the difference did not reach statistical significance.
It remains unclear why dietary and circulating folate among non-multivitamin users may be inversely associated with risk, Figueiredo says.
The study has been published in the Journal of the National Cancer Institute.