Millions of Americans take daily multivitamin/mineral pills, which are by far the most commonly used supplements. They may have felt somewhat 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. Meanwhile,randomized clinical 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 was 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.
The cancer study couldn’t specify which types of cancer were prevented because the numbers were too small for each one— except that there was no effect on prostate cancer.
It also could not assess which particular vitamins and minerals may have been responsible for the observed benefit. Multivitamin formulas and dosages vary greatly. The one used in this study provided about 100 percent of the Daily Values for most vitamins and minerals and was similar to many basic store-brand multis.
It’s not known whether multivitamins may also help reduce the risk of cancer in women, younger men or various racial/ethnic groups, since there have been no comparable multivitamin studies involving them.
The men in the study, being physicians, were mostly well-nourished; it’s possible that people with poorer diets would benefit more. Researchers are continuing to follow the men, and results may further improve over a longer period, since cancer can take decades to develop. Or the apparent cancer benefit may disappear.
Bottom line: If you want to take a multi, there’s no reason to choose more than a basic formula supplying 100 percent of the Daily Values for most vitamins and minerals (look for one with no iron if you’re a man or postmenopausal woman). Some multis supply excessive doses—1,000 percent of the Daily Values or more.
The following groups are most likely to have nutritional needs that a multi may fill: people over 60, women of childbearing age, strict vegetarians and people on weight-loss diets.
But keep in mind, a multi can’t substitute for a healthy, balanced diet. Foods— particularly fruits, vegetables and whole grains—provide many potentially beneficial compounds not found in any pill.