Vitamins and Supplements: Do They Work?

The picture is mixed, but thumbs up for vitamin D and calcium.

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The following article comes from the U.S. News ebook, How to Live to 100, which is now available for purchase.

Vitamins and dietary supplements are big—more than 110 million Americans forked over a collective $28 billion in 2010 on little bottles of would-be health magic. Research is unclear, however, on whether shoring up your diet with extra vitamins, minerals, and other supplements helps or hurts—in the short run or in reaching for the century mark.

[See Best Diets Overall.]

For more than a decade, for example, researchers followed 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. In 2008, study participants received phone calls and letters: Stop the pills. Not only was the answer "no," but vitamin E apparently increased the chance of prostate cancer, if very slightly, and selenium seemed to do the same to diabetes risk. Later the same year, researchers from the Physicians' Health Study-II reported that neither vitamin E nor vitamin C reduced the chances of major cardiovascular problems or cancer as hoped.

[See Best Diets for Healthy Eating.]

That so many people seem to believe they need to boost their intake of vitamins and supplements is a triumph of marketing. Most Americans are well-nourished (besides being amply fed). Because much of our food is fortified with nutrients, once-common deficiency diseases such as scurvy and rickets, caused by inadequate 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. Over the 22-year course of the Iowa Women's Health Study, supplemental vitamin B6, folic acid, iron, magnesium, and zinc were associated with a slightly higher risk of premature death, copper to an 18 percent increased risk. Findings were published last year in the Archives of Internal Medicine. The study authors highlighted concerns about the long-term use of supplements and vitamins among those who do not have severe nutritional deficiencies. The pills, they concluded, are best used when recommended by doctors—not for general prevention.

[See To Supplement or Not to Supplement?]

A 2009 editorial in the Journal of the National Cancer Institute, meanwhile, warned that most vitamin studies show no cancer benefits, and that some found unexpected harm. Two studies of supplemental beta carotene, for example, found higher lung cancer rates, and folic acid research suggested a higher risk of colon polyps among those taking supplements than among those in a placebo group.

Still, some researchers maintain that the diets of many Americans fall somewhat short on certain key nutrients—not enough to threaten a return of those debilitating deficiency diseases, but perhaps enough to call for a little extra help. What follows is the current thinking—pro and con—on popular key supplements that have been well-studied.

Multivitamins. 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, a nutrition advocacy group in Washington, D.C. There's no need for anything fancy that claims "heart health" or "prostate health" benefits, he says; an inexpensive, basic brand is fine. In 2008, 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 about breast cancer risk, but prostate cancer still worries him.