Millions of Americans take a daily multivitamin hoping it will help keep them healthy, and now a large clinical trial has shown that it actually has a modest effect on preventing cancer—at least in older men.
The long-running Brigham and Women’s Hospital study involved nearly 15,000 male physicians over age 50 and found that those who took a Centrum Silver multivitamin, for an average of 11 years, had an 8 percent lower risk of getting cancer compared with those who were randomly chosen to get placebos.
“This is a modest reduction, but our results suggest that low doses of multiple vitamins and minerals in a supplement might work together to prevent disease beyond addressing vitamin and mineral deficiencies,” said study co-author Howard Sesso, an associate epidemiologist in the Brigham’s Division of Preventive Medicine.
The results contrast with findings of some previous research of individual vitamins, which showed either no reduction in cancer risk, or even a small increase.
Sesso and his colleagues presented the findings Wednesday at the American Association for Cancer Research meeting in Anaheim, Calif., and published the study online in the Journal of the American Medical Association.
Taking multivitamins wasn’t found to lead to fewer deaths from cancer. There was a slight difference in mortality favoring supplements, but because of the small number of cancer deaths among the doctors, that difference was not statistically significant.
The men in the study tended to be white non-smokers, who ate little red meat and about four servings of fruits and vegetables a day, and nutritional researchers not involved in the study noted that the cancer preventive benefits may not apply to everyone.
“These are very encouraging results, but women weren’t included in this study, nor were younger men, nor those from a range of ethnicities,” said Dr. Demetrius Albanes, a nutritional epidemiologist at the National Cancer Institute. “It’s one trial, and we’ve seen many cases where one trial doesn’t always give the final answer.”
A study Albanes helped conduct nearly two decades ago found that male smokers who took vitamin E and beta carotene supplements weren’t any less likely to get lung cancer than those who took placebos and that beta carotene may have actually raised the risk of cancer. The surprising finding led some doctors to stop recommending vitamins altogether.
Highly-respected entities such as the US Preventive Services Task Force and the National Institutes of Health Office of Dietary Supplements have for years stated that there’s insufficient evidence to recommend for or against a daily multivitamin, and whether that advice will change remains to be seen.
Laboratory research has shown that vitamins and minerals could protect against cancer by preventing the growth and proliferation of cancer cells, reducing the formation of blood vessels that help cancer spread, and protecting against DNA damage that could give rise to cancer cells. “That’s just a short list of what these nutrients do,” said Albanes. But getting the right level of nutrients in the right balance appears vital for cancer prevention.
The American Cancer Society said it hasn’t decided whether to alter its recommendation that people get nutrients from a healthy diet, not supplements. “This study is an important addition to the body of evidence the Society reviews in establishing its guidelines,” Susan Gapstur, the organization’s vice president of epidemiology research, said in a statement. “Typically, we like to see these kinds of findings replicated by other studies, and in other populations.”
The Brigham researchers didn’t find any downsides to taking a daily supplement that contains no more than the recommended daily allowance for most vitamins and minerals. Study co-author Dr. JoAnn Manson said the findings “underscore the principle that more isn’t necessarily better.”
While it’s not certain whether the results apply to women, Manson said “there’s no strong biological basis for assuming that these results would apply only to men.” The study didn’t find that multivitamins were any more effective at protecting against prostate cancer, which occurs only in men, as compared with non-gender specific cancers such as leukemia, lung, and colon cancer.
In the study, 1,290 men out of 7,317 who took multivitamins were diagnosed with cancer compared with 1,379 cancer diagnoses in the 7,324 men who took placebos.
Some nutrition experts, however, said the new findings shouldn’t sway people to take a multivitamin. “I don’t take a multivitamin, and I’m not planning to start taking one,” said Marion Nestle, a nutrition professor at New York University. “I’m not at all impressed with this evidence that they matter for most people. In fact, if you eat a lot of processed foods, which are often fortified, you’re getting the same vitamins and minerals found in these supplements.”
Consumers will, no doubt, draw their own conclusions from the findings and decide for themselves whether to purchase an over-the-counter multivitamin for nickel or two a pill.
Study participant Dr. David Chapin, a gynecologist at Beth Israel Deaconess Medical Center who recently found out he had been taking a placebo, said he’s probably going to start taking a daily supplement since it “seems silly not to” given the minimal risk and modest benefits. Harvard Medical School nutrition professor Dr. George Blackburn, who also participated in the study, said he also plans to taking multivitamins.