Taking a daily multivitamin does not lower the risk of stroke or heart attack in middle-aged and older men, according to a large study published Monday in the Journal of the American Medical Association (JAMA).

The study, conducted by researchers at Harvard Medical School and the Harvard School of Public Health, followed 14,641 male doctors who had volunteered to participate in the ongoing Physician’s Health Study II. The mean age of the doctors at the start of the study (1997) was 64 years.

The doctors were randomly assigned to take either a daily multivitamin (Pfizer’s Centrum Silver) or a placebo. After 11 years, there were 1,732 cases of cardiovascular “events,” such as heart attacks and strokes, but the rate of those events did not show a statistically significant difference between the multivitamin and placebo groups.

The study has its limitations, of course. The doctors were generally healthy, with relatively good dietary habits. Few smoked (less than 4 percent) and most exercised at least once a week (about 60 percent). It’s not clear, therefore, if the findings would be similar in other, less healthy populations.

But research suggests that it would. In 2009, another large study, this time involving more than 160,000 women, also found that taking a daily multivitamin did nothing to lower the risk of heart disease.

The women’s study found, in addition, no association between vitamin supplements and cancer risk. The Physician’s Health Study II, other the other hand, did find a modest (8 percent) decrease in the overall cancer risk in men who were taking multivitamins. Those results were published in JAMA last month.

That finding, however, contrasted with other recent studies that have suggested taking supplements may do more harm than good. A 2011 study involving 35,000 men reported, for example, that taking supplements of vitamin E and selenium (both of which are usually found in multivitamins) was associated with a slightly higher risk of developing prostate cancer. And a study involving 38,000 Iowa women reported that older women who took multivitamins and other supplements were 2.4 percent more likely to die during a 19-year period than their peers who did not use supplements.

‘A distraction’ from effective preventions

As Dr. Eva Lonn, a professor of cardiology at McMaster University in Hamilton, Ontario, points out in an editorial that accompanies the JAMA study, 40 percent of Americans spend billion of dollars each year on multivitamins, despite the lack of evidence that the pills offer any health benefits to most people. (There are, of course, some people, including pregnant women and individuals with specific vitamin-deficiency-related diseases, whose health does benefit from supplements.)

But the unnecessary economic burden on consumers is not what’s most troubling to Lonn and other health officials. She’s concerned that people who take multivitamins may be less likely to engage in proven preventive health behaviors.

“Many people with heart disease risk factors or previous [cardiovascular disease] events lead sedentary lifestyles, eat processed or fast foods, continue to smoke, and stop taking lifesaving prescribed medications, but purchase and regularly use vitamins and other dietary supplements, in the hope that this approach will prevent a future [heart attack] or stroke,” she writes. “This distraction from effective [cardiovascular disease] prevention is the main hazard of using vitamins and other unproven supplements. The message needs to remain simple and focused: [cardiovascular disease] is largely preventable, and this can be achieved by eating healthy foods, exercising regularly, avoiding tobacco products, and, for those with high risk factor levels or previous [cardiovascular disease] events, taking proven, safe, and effective medications.”

The JAMA study is available free on the publication’s website. Lonn’s editorial, however, is behind a paywall.