Vitamins and Supplements: Do They Work?

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Late in October, just before his 65th birthday, Robert Marks got a phone call: Stop the pills. For more than a decade, the retired Lutheran minister from Grapeville, Pa., had been among more than 35,000 men enrolled in SELECT, a clinical trial designed to see whether taking selenium and vitamin E might help prevent prostate cancer. But as a letter following up the call explained, not only was the answer "no," but vitamin E apparently increased the chance of prostate cancer, if very slightly, and selenium seemed to raise the risk of diabetes.

The news was another blow in the general battering of vitamin and mineral supplements as weapons in fending off chronic and age-related diseases like cancer and heart disease. In November, researchers from the Physicians' Health Study-II reported that neither vitamin E nor vitamin C reduced the odds of major cardiovascular problems. A few days later, researchers said that more data from the study showed those vitamins didn't help stave off cancer, either. And another recent study found that supplemental B vitamins, including folic acid, didn't lower the risk of breast or other cancers.

Americans are amply fed and, for the most part, well nourished. Because much of our food is fortified with nutrients, once common deficiency diseases such as scurvy and rickets (caused by a lack of vitamin C and D, respectively) have nearly disappeared in this and other developed countries. Researchers generally believe that with a few exceptions, like pregnant women or the elderly, most people don't need supplements.

But if bottles of vitamins and nutritional supplements line your medicine cabinet shelves, hold off before going completely cold turkey. Some researchers maintain that the diets of many Americans still fall short on several essential nutrients—not enough to cause those debilitating deficiency diseases, but perhaps enough to miss out on their benefits without extra help from supplements. While experts say you should be skeptical of most claims about the disease-preventing power of vitamins and minerals, some evidence does support taking a few as a hedge. What follows is the current thinking—pro and con—on some key supplements that are both popular and well studied.

Multivitamins. Millions of people pop a multivitamin every day with little evidence that it does any good. The U.S. Preventive Services Task Force neither recommends nor advises against multivitamins (or other supplements) for preventing cancer or cardiovascular disease. Yet many researchers say a multivitamin has a role as "a very inexpensive insurance policy," says David Schardt, senior nutritionist at the Center for Science in the Public Interest. There's no need for anything fancy that claims "heart health" or "prostate health" benefits, he says; an inexpensive, basic brand is fine. Earlier this year, Harvard Men's Health Watch newsletter editor Harvey Simon recommended against multivitamins. His chief worry was that on top of already fortified foods, the folate in a multi could spur cancer. But a study since then showed that cancer was not increased in women at risk for heart problems who were given folic acid supplements. Simon is now less concerned, at least with regard to breast cancer—prostate cancer still worries him. 

Calcium and vitamin D. Thumbs up. Extra calcium to protect bone health is safe and routinely prescribed for women who get too little from food. And consensus is building that Americans get too little vitamin D, which promotes calcium uptake. It is produced by sun-exposed skin and is difficult to get from unfortified foods—fatty fish are the only major food source. Studies suggest vitamin D also may help fend off cancer and ward off infections. Researchers are hungry for more evidence. "We really need to do the studies," says Len Lichtenfeld, deputy chief medical officer for the American Cancer Society.

The Institute of Medicine has announced it will review the daily recommended dietary allowance of vitamin D, now from 200 to 600 international units depending on age, gender, and race. Experts put the high end anywhere from 800 IU to 2,000 IU a day. The IOM review is due in early 2010. Until then, while the benefits are unproven, adding 1,000 IU of vitamin D won't likely hurt and could help, especially for people who don't get much sun.

Clarified on 12/10/08: An earlier version of this article stated that Harvard Men's Health Watch newsletter editor Harvey Simon says his concerns about multivitamins have recently eased. They have eased somewhat for breast cancer but not prostate cancer.