Folic acid may reduce birth defects and offer numerous other health benefits, but too much of the vitamin may raise the risk of prostate cancer, a surprising study has found.
The study, in the March 10 online issue of the Journal of the National Cancer Institute, found that men who took a daily folic acid supplement of 1 mg daily had more than twice the risk of prostate cancer compared with men who took a placebo.
Folic acid is a B vitamin that has been proven to reduce birth defects in infants if taken before and during pregnancy. But its effects on other conditions, including cancer, are unclear.
One study, called the Aspirin/Folate Polyp Prevention Study (AFPP), conducted between 1994 and 2006, found that while aspirin reduced the risk of colon polyps, folic acid actually increased the risk of advanced and multiple polyps.
In this latest study, researchers at the University of Southern California (USC), looked at prostate cancer rates among 643 men who took either 1 mg folic acid supplements a day or a placebo in the AFPP study and who enrolled in an extended follow-up study.
They found that the estimated prostate cancer risk was 9.7 per cent at 10 years in men who took the folic acid, compared with 3.3 per cent in men who took the placebo, reports the study's lead author Jane Figueiredo, assistant professor of preventive medicine at the Keck School of Medicine of USC.
Interestingly, the men who had high levels of folate in their blood and who ate foods rich in folate -- which include leafy green vegetables and dried beans -- seemed to have a reduced risk of prostate cancer. But the researchers say the difference was not statistically significant.
Figueiredo said the findings are preliminary and is not prepared to recommend that men not take folic acid supplements. More research needs to be done to determine the level of risk from the vitamin.
Folic acid is the synthetic form of folate. It's not clear why folate was not linked to higher protate cancer rates as flic acid was.
Dr. Joel Mason, director of the Vitamin and Carcinogenesis Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston, who was not involved in the study, tells CTV.ca that research into whether there are differences between folic acid and folate is ongoing.
He says it's possible that volunteers in studies in which links were found between folic acid and cancer may simply have taken in too much folate.
But, he says, there has also been some concern over the years that folic acid has characteristics that are unique to itself -- and not to more natural forms of folate -- that are responsible for the cancer link.
"That is speculation," he emphasizes. "Unfortunately, this is a field that no one yet really understands well and so we're kind of stumbling in the dark a bit.
"And it's a little scary because of the issue of folic acid fortification of cereals and grains and the widespread use of vitamin supplements."
It's well-known that adequate folate levels are important in the prevention of neural tube defects, cardiovascular and neurological diseases, as well as several cancer types, such as pancreatic and stomach cancer.
Mason explains that folate is essential because it facilitates the synthesis and repair of DNA. But it may cause problems in those who have the very earliest stages of cancer: pre-cancerous cells.
"Cancer and pre-cancerous cells divide more rapidly than normal cells, by definition," he explains. "So if you give them a lot of this factor that enables them to synthesize DNA more rapidly, then it's going to allow them to proliferate more rapidly."
