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About one third of Americans take a daily multivitamin. The reasons vary. Some people want to supplement their already healthy diet. Pregnant women are often advised to take them, as are vegetarians.  Some people have chronic illnesses that require them.  But no matter the reason, most people take multivitamins as a quick way to supplement vitamins and minerals that they may not get from their daily diet. 

According to a report from the University of California-Berkeley School of Public Health’s 2013 Wellness Report on Dietary Supplements, Americans spend about $28 billion per year on supplements, such as multivitamins and herbal supplements, and the industry continues to grow.

What are supplements?

A dietary supplement is a substance taken by mouth, most often in pill form.  It usually contains a concentrated dose of a vitamin, mineral, herb, amino acid, plant extract, or hormone. 

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The main purpose of supplements, of course, is to fill in your diet with concentrated doses of a substance you need – usually essential vitamins or minerals – that for whatever reason, you’re not getting in your diet. 

What do the studies say?

As supplements have come into popular use, they’ve been subjected to scientific study, though perhaps not as systematically as they should be.  A growing body of research, and some recent studies in particular, seem to paint a mixed picture of the benefits of supplements, specifically multivitamins.

 In October 2012, the Journal of the American Medical Association (JAMA) found that the use of a daily multivitamin in men was associated with about an 8 percent reduction in cancer cases over 10 years. 

A couple of weeks later, JAMA came out with another study that found that the use of a daily multivitamin in men has no impact on their cardiovascular health. 

Both of these findings came from an analysis of one big study called the Physicians’ Health Study II.  This is a database of 14,641 male U.S. physicians, aged 50 or older.  The study has tracked the men throughout their lives, taking note of lifestyle habits, any diseases they may develop, and cause of death once it occurs.

For this particular study on multivitamins, half of the men were given a daily multivitamin and the other half were given a placebo.  This is significant because most studies on multivitamins have been purely observational--meaning that the study participants are not asked to change anything about their lifestyle, and no control group is used to test the causality of a result.

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These JAMA studies were large-scale, randomized, double blind and placebo-controlled, which allowed researchers to say with some certainty that the multivitamins were the cause of the results.  In this case, the results were a modest reduction in cancer, but no discernible difference in cardiovascular health.