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.
For more on cancer prevention and nutrition, visit the American Cancer Society.
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, Jou
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