November 4 (HealthDay News) -- Taking folic acid or other B vitamin supplements won't lower your risk of cancer, new research shows.

However, the good news is that it won't increase your risk either, according to the study, which was published in the Nov. 5 issue of the Journal of the American Medical Association.

"In women at risk of cardiovascular disease, we found that folic acid, vitamin B6 and vitamin B12 had no beneficial or harmful effects on the risk of invasive cancer or breast cancer," said study author Dr. Shumin Zhang, an associate professor of medicine at Brigham and Women's Hospital and Harvard Medical School, in Boston.

Because adequate levels of folic acid in women have been proven to prevent serious birth defects, the government has mandated that folic acid be added to cereals and breads since January 1998, according to the U.S. Centers for Disease Control and Prevention.

Additionally, about one-third of U.S. adults take a daily multi-vitamin that contains folic acid, B6 and B12, according to the study. Some studies have suggested that supplements of these nutrients might be protective against cancer, though results have been inconsistent, according to background information in the study.

One study even suggested that such supplements might raise the risk of cancer.

To address these concerns, Zhang and colleagues reviewed data on 5,442 women who participated in the Women's Antioxidant and Folic Acid Cardiovascular Study. All of the women were over 42 years old, and had either preexisting cardiac disease or three or more risk factors for heart disease.

The study participants were randomly assigned to receive either a supplement containing 2.5 milligrams (mg) of folic acid, 50 mg of vitamin B6 and 1 mg of vitamin B12, or a placebo. The study lasted 7.3 years, from April 1998 through July 2005.

During that time, 379 women developed invasive cancer -- 187 in the active treatment group and 192 in the placebo group. Of the women who developed cancer, 154 developed breast cancer -- 70 in the active treatment group and 84 in the placebo group. None of these differences were statistically significant.

However, when the researchers broke the data down by age, they did note what appeared to be a protective effect from the supplement treatment in women over 65. Zhang said this might be because older women generally have a higher need for these nutrients. But she also said these results should be "interpreted with caution," because the study wasn't designed to look at age differences. "It's something that needs further study," she added.

Victoria Stevens, strategic director of laboratory services for the American Cancer Society, agreed. "There was a suggestion of a protective effect in older women that I think is worth following-up," Stevens said.

The bottom line, according to Stevens, is that "supplements aren't a magic bullet" for cancer prevention.

"There are really good reasons for women to take folic acid, especially if they're planning on having a baby, because there's really conclusive evidence that it can reduce birth defects. But, for the average woman in terms of cancer risk, folic acid and B vitamins don't seem to increase or reduce risk," Zhang said.

SOURCES: Shumin Zhang, M.D., Sc.D., associate professor, medicine, Brigham and Women's Hospital and Harvard Medical School, Boston; Victoria Stevens, Ph.D., strategic director, laboratory services, American Cancer Society, Atlanta; Nov. 5, 2008, Journal of the American Medical Association