The first major study of long-term daily multivitamin use by nearly 15,000 older men found that it has a modest effect in reducing overall cancer but not, unfortunately, in lowering the risk for prostate cancer.
The study was published online today in the Journal of the American Medical Association, to coincide with the American Association for Cancer Research meeting in Anaheim.
Multivitamins are the most common dietary supplement, regularly taken by at least one-third of U.S. adults. Although there has been no hard evidence that taking a multivitamin can prevent cancer or any other chronic disease, many Americans take the supplements anyway, figuring they can't hurt and they might help.
Researchers with Brigham and Women's Hospital and Harvard Medical School in Boston, who conducted the study, found that older men who took multivitamins over an 11-year period had an 8 percent lower incidence of cancer - a small but statistically significant reduction.
"It's a very mild effect [but] ... at least this doesn't suggest a harm," as some previous studies on single vitamins have, Ernest Hawk, M.D., vice president of cancer prevention at the University of Texas MD Anderson Cancer Center and formerly of the National Cancer Institute told the Associated Press.
The research was part of the Physicians Health Study II, a randomized, double-blind, placebo-controlled study of 14,641 male U.S. physicians who were age 50 or older when the study began in 1997. Previous trials that looked at whether taking individual supplements, like vitamin E or C, would protect against cancer have found either no benefit or, in the case of vitamin E, an increased risk of prostate cancer.
This new study, however, looked at multivitamins, which offer a broad, low-dose combination of nutrients that more closely mirrors a healthy diet. Subjects either took a daily multivitamin (Centrum Silver, formulated for age 50-plus) or an equivalent placebo.
Although researchers found that the men taking the multivitamin had less cancer overall, there was no significant effect on the rate of prostate cancer. There was also no significant reduction in certain site-specific types of cancer, such as colorectal, lung or bladder, or in overall cancer deaths.
And while the overall reduction in cancer for vitamin takers was 8 percent, the actual number of men protected from cancer was pretty small: Among multivitamin users, there were 17 incidents of cancer per 1,000 persons in a year, compared with 18.3 cancer cases per 1,000 in the placebo group. That's a little more than a one-cancer-case-per-year difference between the two groups.
Still, researchers concluded that the results support "the potential use of multivitamin supplements in the prevention of cancer in middle-aged and older men."
They also noted that multivitamins may have different results in women, younger men or older men less healthy than those in this study.
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