By Liz Szabo, USA TODAY
Researchers have more disappointing news for people who hope to protect their health with vitamins.
In the longest-running trial of its kind, doctors found that folic acid and other B vitamins didn't prevent breast cancer or cancer in general, according to a seven-year study of 5,442 women in today's Journal of the American Medical Association.
Researchers randomly assigned some of the women to take the supplements folic acid, vitamin B-6 and vitamin B-12 and others to get placebos. Neither the women nor their doctors knew which pills they were taking a type of trial that is widely considered the "gold standard" for medical evidence.
Despite the negative results, some women should still take folic acid, says author Shumin Zhang, an epidemiologist at Boston's Brigham and Women's Hospital and Harvard Medical School. Experts recommend that women who are pregnant or of childbearing age take folic acid because it has been shown to prevent neural-tube defects, such as spina bifida.
But Zhang's paper is the latest in a series of large, well-designed studies that fail to show that vitamins prevent cancer. These same B vitamins also failed to cut the risk of heart disease, according to a study published in JAMA in May.
Last week, the National Cancer Institute stopped a trial of 35,000 men after finding that the antioxidants vitamin E and selenium didn't prevent prostate cancer but could increase some health risks. And last year, a large analysis in JAMAfound that the risk of premature death increased 7% for people who take beta-carotene, 16% for those who take vitamin A and 4% for vitamin E.
"It would be wonderful if taking a pill could reduce our risk of developing any kind of cancer," says the American Cancer Society's Michael Thun, who wasn't involved in the new study. "People are hoping for an easy solution, and that's difficult to find."
The only trial to really prove that supplements reduce cancer risk was done in malnourished people in China, Thun says. In communities where most people have adequate overall nutrition, vitamins don't seem to have much of an effect. That may be particularly true for health-conscious people with the money to afford supplements, he says: "The people who are most likely to take multivitamin supplements are the least likely to have a vitamin deficiency."
Yet Thun notes that vitamins could have had small benefits that Zhang's study wasn't large enough to detect. And because cancer can take many years to develop, even a seven-year study may not have been long enough to measure the vitamins' effects, authors say.
Zhang says she noticed one intriguing trend: Among those taking the vitamins, women who were 65 and older had a lower risk of breast cancer and cancer in general. That makes sense, she says, because older people need more of these vitamins in their diets, although the finding based on an analysis that broke the data down according to numerous factors could have been the result of chance. Scientists will have to do a lot more research to fully understand if older women really benefit, she says.