Millions of Americans take daily multivitamin/mineral pills, which are by far the most commonly used supplements. Ask them why, and most will say they take the pills to make up for nutritional shortfalls in their diet, to help prevent a variety of diseases, or just to stay healthy in general.
And yet, there has been remarkably little solid, consistent evidence to back up the purported benefits of multivitamins (the same is true of individual vitamin or mineral supplements).
So multi users may have felt half-vindicated by two recent Harvard studies in the Journal of the American Medical Association, one focusing on cancer, the other on cardiovascular disease.
Over the years, many large studies have observed that people who take a multi have a lower risk of heart attacks, various cancers, and other diseases—though other observational studies have not, and a few have suggested increased risks. Still, such studies can’t prove cause and effect, since people who take multis on their own may be more health-conscious than non-users and may be healthier (or perhaps less healthy) to begin with.
That’s where randomized clinical trials, which compare an intervention such as a drug to a placebo, come in. But such trials on multis have been relatively small and short and have yielded mostly disappointing results. Thus, a few years ago, a panel of advisers at the National Institutes of Health concluded that the evidence concerning multivitamins is limited and inconclusive.
The new Harvard studies both involved 14,641 male doctors over 50, who were part of the long-running Physicians’ Health Study. Half were randomly assigned a basic daily multivitamin/mineral pill for "seniors," and half were given a placebo. Theywere followed for an average of 11 years.
The first study found that the multi users were 8 percent less likely to develop cancer. That’s a modest reduction in risk for an individual, but it adds up across the population,working out to 13 cases of cancer prevented among 1,000 men taking a multi for a decade. Cancer mortality rates were not significantly reduced in the multi group.
The second study found no reduction in heart attacks, strokes, or cardiovascular deaths in the multi group. There were no major adverse effects in either study.