Multivitamin/mineral pills are the most commonly used supplements in the United States. A multi can be a good way to make up for nutritional shortfalls. But many people expect too much from their multivitamins, which are purported to help prevent a wide range of diseases. Over the years, various observational studies have indeed suggested that people who take a multi have a lower risk of various diseases. The results of clinical trials, however, have been largely disappointing.
What the studies show
A few years ago, a panel of advisors at the National Institutes of Health concluded that the evidence concerning the effectiveness and safety of multivitamins is limited and inconclusive.
A 2009 study published in the Archives of Internal Medicine analyzed data from the landmark Women’s Health Initiative and found that multivitamin use did not reduce the risk of cancer or cardiovascular disease. Meanwhile, two studies published in the American Journal of Clinical Nutrition in 2010 analyzed a decade of data from more than 30,000 Swedish women. One found that women who took multivitamins were 27 percent less likely to have a heart attack. In contrast, the second study linked multivitamin use to a 19 percent increased risk of breast cancer. Still, these were observational studies, and do not prove cause and effect.
In 2012, two clinical trials from Harvard involving 14,600 physicians found that those taking a basic multivitamin were eight percent less likely to develop cancer over 11 years compared to those taking a placebo. But they did not have a reduced risk of heart attack or stroke. In 2013, an Australian meta-analysis of 21 randomized controlled trials, published in the American Journal of Clinical Nutrition, concluded that multivitamin use has no effect on all-cause mortality rates.
Of course, multivitamins vary greatly, so even if there are benefits, it would be very hard to know which components are responsible, or at what doses.
A risk of taking too much?
Multivitamins are generally assumed to be safe, but some contain excessive doses of nutrients—10 or more times the recommended daily intakes. For instance, large doses of copper can interfere with the absorption of zinc, and vice versa.
Are you a candidate?
Consider taking a daily multi if you are in one of the following groups.
• You are a woman of childbearing age. Women capable of becoming pregnant need at least 400 micrograms daily of folate (the form in supplements is called folic acid). This B vitamin helps prevent neural tube birth defects. In addition, premenopausal women can benefit from the iron in a basic multi.
• You are pregnant or breastfeeding. You should probably take a multi, but discuss your special needs with your doctor.
• You are on a weight-loss diet or are a heavy smoker or drinker.
But keep in mind
If you take a multivitamin/mineral pill, it cannot substitute for a healthy, balanced diet. Foods—particularly fruits, vegetables and whole grains—provide fiber as well as many potentially beneficial compounds not found in any pill.
Originally published January 2013. Updated January 2014.