Folic acid supplements linked to prostate cancer risk
From Wednesday's Globe and Mail
March 11, 2009 at 8:33 AM EDT
New research suggests that men who take folic acid supplements may be putting themselves at significantly greater risk for developing prostate cancer, which raises fresh questions about the safety and efficacy of taking vitamins for disease prevention.
The findings add to a growing body of evidence that too much folic acid may not protect against certain types of cancer.
The study involved nearly 650 men who either took daily folic acid supplements of one milligram or a placebo. Researchers, who followed the men for about 10 years, found those who took folic acid supplements had a risk of developing prostate cancer double that of those who took placebos.
More than 1,200 runners participated in the annual Harry's Spring Run-Off to fight prostate cancer last weekend in Vancouver's Stanley Park.
"We didn't expect it to be harmful," said Jane Figueiredo, assistant professor of preventative medicine at the University of Southern California's Keck School of Medicine in Los Angeles.
"But it's sort of like a threshold effect. If you get too much, we now know the safety of chronic high exposure to folate might not be as good as what we hoped for."
The study, published online yesterday at the Journal of the National Cancer Institute website, was conducted using research collected for an earlier study examining the links between folic acid, aspirin and colorectal cancer.
Folic acid is the synthetic form of folate, which is a B vitamin that occurs naturally in leafy greens and other fruits and vegetables. It helps produce and maintain healthy cells and is involved in numerous biological functions.
In recent years, public health officials have urged women of child-bearing age to take folic acid supplements because the nutrient reduces the chances of have a baby with a birth defect such as spina bifida. Folic acid is also added to grain products sold in Canada, such as white flour and enriched pasta, to help ensure that pregnant women have adequate levels.
But a growing amount of evidence indicates too much folic acid - particularly more than one milligram a day - may do more harm than good.
A man would have to take about 2.5 multivitamins a day to ingest one milligram of folic acid, the amount linked to possible prostate cancer risks. But considering folic acid is added to many food products, and that folate occurs naturally in many foods, men who take supplements could easily exceed one milligram a day, according to the study's lead author.
"There's been a large body of evidence again just suggesting too much folate is probably not a good thing," Prof. Figueiredo said.
But that doesn't mean folate is bad. On the contrary, researchers found those men who didn't take folic acid supplements, but had small amounts of naturally occurring folate present in their blood, seemed to have a decreased incidence of prostate cancer.
"What we're seeing is many of them [supplements] are not appearing to be beneficial in the way that we had anticipated and could be harmful," Prof. Figueiredo said.
An editorial published with the study questions the use of multivitamins and supplements to prevent cancer and other diseases.
"The prospects for cancer prevention through micronutrient supplementation have never looked worse," Alan Kristal of the Fred Hutchinson Cancer Research Center in Seattle and Scott Lippman of the department of thoracic/head and neck medical oncology at the University of Texas M.D. Anderson Cancer Center.
The authors noted that several large credible studies, including research into the effects of vitamins C and E and beta carotene, found the supplements did not seem to help prevent cancer.
Prof. Figueiredo said the findings are too preliminary to warrant a recommendation against taking folic acid supplements. She said more research must be conducted to determine the level of risk too much folate could have, but that it's also important to remember a healthy diet is, in many ways, a good defence against disease.