Deciding what to eat for dinner can be mind-bending. How do we keep track of the ever-evolving recommendations for what to put on, and leave off, the plate? Red meat might cause cancer! But don't replace it with tofu—soy concoctions might be carcinogenic, too! Don't even try to figure out where carbs stand this week. And the verdict on coffee, chocolate, and alcohol changes faster than you can order a mocha martini.
Vitamins—with their promise to bridge the gap between the nutrients our bodies need and those they get—have always seemed reassuringly simple: Just pop a multivitamin and let your body soak in those extra nutrients. But not any longer. During the past few years, study after study has raised doubts about what, if any, good vitamins actually do a body. They could even pose some real medical risks.
Half of all American adults take some sort of nutritional supplement. But research on a wide variety of patient populations and medical conditions has failed to find much evidence that multivitamins, the most commonly used of the lot, prevent major chronic diseases in healthy people. The most recent knock came this spring, when a study of more than 160,000 post-menopausal women, published in the Archives of Internal Medicine, found that the all-in-one pills did not prevent cancer, heart attacks, or strokes and did not reduce overall mortality.
Individual vitamins and minerals haven't fared much better under scientific scrutiny, with research debunking some of the reputed benefits of vitamin B6, calcium, niacin, and others. In 2006, the National Institutes of Health convened an independent panel of experts to evaluate the evidence that vitamins could prevent chronic disease. The scientists ultimately issued a report stating that studies "do not provide strong evidence for beneficial health-related effects of supplements taken singly, in pairs, or in combinations."
The news on antioxidants, the darlings of the vitamin menagerie, is even more troubling. These compounds, which include vitamins A, C, and E, selenium, beta carotene, and folate, fight free radicals, unstable compounds thought to damage cells and contribute to aging. But not only do antioxidant supplements fail to protect against heart disease, stroke, and cancer; they actually increase the risk of death, according to a 2007 analysis of research on more than 232,000 people, published in the Journal of the American Medical Association, as well as other studies.
Exactly why they might increase mortality is unclear, but doctors at prominent research institutions—including New York's Memorial Sloan-Kettering Cancer Center and Seattle's Fred Hutchinson Cancer Research Center—have highlighted some unsettling connections between supplemental antioxidants and an increased risk of a variety of cancers. Popping certain kinds of antioxidant pills can feed latent cancers growing in the body, for instance, and reduce the effectiveness of chemotherapy. These observations make a certain intuitive sense, since vitamins and minerals play an important role in the replication of healthy cells—why shouldn't they be doing the same for cancerous cells? (Feeding mice a diet poor in antioxidants, on the other hand, can actually help shrink their brain tumors.) Scientists are also beginning to suspect that the body may actually need free radicals—which help kill cancer cells, ensure optimal immune function, and regulate blood sugar, among other things—so we shouldn't necessarily be mopping them all up.
The list of worrisome findings goes on, but it doesn't seem to have put a dent in the $25 billion supplement industry. Sales are not only robust but rising in the United States. Doctors still recommend multivitamins as part of basic preventative care. Despite the demonstrated risk, as many as 80 percent of cancer survivors swallow a daily dose, according to a study published in the Journal of Clinical Oncology in 2008.