MONDAY, Oct. 11, 2010 (HealthDay News) -- Despite reducing levels of a protein associated with heart disease, supplements containing the B vitamin folic acid don't reduce the risk for cardiovascular disease, death or cancer, according to a new large-scale analysis of studies on the issue.
Folic acid helps prevent devastating neural tube birth defects such as spina bifida. Since it also lowers blood levels of the protein homocysteine, which is linked with heart and blood vessel disease and other ills, some scientists hoped that the powerful vitamin might lower the risk of heart disease, stroke or cancer.
The current meta-analysis suggests that even taken at high doses, folic acid supplements don't have that effect.
The report is published in the Oct. 11 issue of the Archives of Internal Medicine.
"Vitamins are necessary to prevent diseases of deficiency like scurvy and rickets, but more is not necessarily better and may be harmful," said Dr. Jeffrey A. Tice, assistant professor of medicine in residence at the University of California, San Francisco and author of an accompanying journal editorial.
To examine folic acid supplements' possible role in preventing cancer, heart disease or stroke, a team led by Robert Clarke, from the University of Oxford in England, collected data on 37,485 people who took part in eight trials comparing the value of folic acid supplements against placebo. These trials represented all the large randomized studies available that were designed to lower plasma homocysteine levels for the prevention of cardiovascular disease.
Over five years, there were 9,326 major coronary events, including strokes and new heart procedures. In addition, 3,010 patients developed cancer and 5,125 people died, according to the report.
Even though those taking folic acid saw a 25 percent reduction in homocysteine levels, they were just as likely to have a heart attack or stroke as those receiving a placebo. In fact, 24.9 percent of these adverse events were among those taking folic acid and 24.8 percent were among those receiving placebo, the researchers found.
There was also no significant difference between the groups in the likelihood of developing cancer (8.7 percent versus 8.2 percent) or dying (13.8 percent versus 13.6 percent), Clarke's group noted.
The researchers acknowledged that some benefit in taking folic acid might emerge after five years -- the length of the study period -- but said that was unlikely because most heart-protective benefits from medications tend to emerge within a few years of treatment.
However, the researchers found no harmful effects from taking folic acid in multivitamin supplements or in folate-fortified foods. (Because getting enough folic acid before and during pregnancy prevents most neural tube birth defects, many cereals and other foods are fortified with folic acid.)
"One-third of adults in the United States and one-quarter of those in the United Kingdom report taking daily multivitamin supplements containing folic acid," the authors write. "Although the lack of any other benefits [other than preventing neural tube defects] is disappointing (albeit fairly definitive), the lack of any significant adverse effects on vascular events, cancer incidence, cancer mortality and overall mortality provides reassurance about the safety of population-wide folic acid fortification," they added.
But, Tice cautioned, high-dose folic acid therapy does not reduce the risk for strokes, heart attacks or cancer.
He also suggested that consumers be cautious about high-dose supplements. "High doses of other vitamins with a strong scientific rationale for long-term health benefits, such as the antioxidants vitamin E and beta carotene, are now known to be harmful," Tice said.
"Be wary of the current enthusiasm for vitamin D and omega-3 fatty acids until large randomized studies are completed," he added. "The best way to optimize your health is to exercise regularly, eat a nutritious diet, avoid smoking and maintain a healthy weight."
For more information on folic acid, visit the U.S. National Library of Medicine.