Taking vitamins you don't need isn't just a waste of money—it could put your health at risk, too.
Myth: A multivitamin can make up for a bad diet
An insurance policy in a pill? If only it were so. One study in the Archives of Internal Medicine looked at findings from the Women's Health Initiative, a long-term study of more than 160,000 midlife women. The data showed that multivitamin-takers are no healthier than those who don't pop the pills, at least when it comes to the big diseases—cancer, heart disease, stroke. "Even women with poor diets weren't helped by taking a multivitamin," says study author Dr. Neuhouser.
Myth: Anyone could benefit from a multivitamin
Vitamin supplements came into vogue in the early 1900s, when it was difficult or impossible for most people to get a wide variety of fresh fruits and vegetables year-round. Back then, vitamin-deficiency diseases weren't unheard-of: the bowed legs and deformed ribs of rickets (caused by a severe shortage of vitamin D) or the skin problems and mental confusion of pellagra (caused by a lack of the B vitamin niacin). But these days, you're extremely unlikely to be seriously deficient if you eat an average American diet, if only because many packaged foods are vitamin-enriched. (Still, watch out for these silent signs of a vitamin deficiency.) Sure, most of us could do with a couple more daily servings of produce, but a multi doesn't do a good job at substituting for those. "Multivitamins have maybe two dozen ingredients—but plants have hundreds of other useful compounds," says Marian Neuhouser, PhD, of the cancer prevention program at the Fred Hutchinson Cancer Research Center in Seattle, Washington. "If you just take a multivitamin, you're missing lots of compounds that may be providing benefits."
Myth: Vitamin pills can prevent heart disease
At one point, researchers hoped antioxidant vitamins like C, E, and beta-carotene could prevent heart disease by reducing the buildup of artery-clogging plaque. B vitamins were promising, too, because folate, B6, and B12 help break down the amino acid homocysteine—and high levels of homocysteine have been linked to heart disease. Unfortunately, none of those hopes have quite panned out. (Don't miss these other secrets vitamin manufacturers are keeping from you.) An analysis of seven vitamin E trials concluded that it didn't cut the risk of stroke or of death from heart disease. The study also scrutinized eight beta-carotene studies and determined that, rather than prevent heart disease, those supplements produced a slight increase in the risk of death. Other big studies have shown vitamin C failing to deliver. As for B vitamins, research shows that yes, these do cut homocysteine levels …but no, that doesn't make a dent in heart danger. One 2016 study of 160 patients with heart failure did find that vitamin D3 supplements boosted heart function (but a placebo didn’t), but more research is needed. Instead of taking pills, the American Heart Association recommends eating a varied diet rich in fruits, vegetables, and whole grains.
Myth: Vitamin C is a cold fighter
In the 1970s, Nobel laureate Linus Pauling popularized the idea that vitamin C could prevent colds. Today, drugstores are full of vitamin C–based remedies. But don’t get dragged in to the hype. In 2013, researchers analyzed a raft of studies going back several decades and involving more than 11,000 subjects to arrive at a disappointing conclusion: Vitamin C didn't ward off colds, except among marathoners, skiers, and soldiers on subarctic exercises. Of course, prevention isn't the only game in town. Taking the vitamin daily does seem to reduce the time you'll spend sniffling—but not enough to notice. Adults typically have cold symptoms for 12 days a year; a daily pill could cut that to 11 days. Kids might go from 28 days of runny noses to 24 per year. Those who took vitamin C every day also had less severe symptoms. Taking C only after symptoms crop up doesn't help, so researchers conclude that patients decide for themselves whether year-round pill-popping for minimal benefit is worth the money.
Myth: Taking vitamins can protect against cancer
Researchers know that unstable molecules called free radicals can damage your cells' DNA, upping the risk of cancer. They also know that antioxidants can stabilize free radicals, theoretically making them much less dangerous. So why not take some extra antioxidants to protect yourself against cancer? Because research so far has shown no good comes from popping such pills. (Unlike these 37 science-backed ways to prevent cancer.) A number of studies have tried and failed to find a benefit, like one that randomly assigned 5,442 women to take either a placebo or a B-vitamin combo. Over the course of more than seven years, all the women experienced similar rates of cancers and cancer deaths. In Dr. Neuhouser's enormous multivitamin study, that pill didn't offer any protection against cancer either. Nor did C, E, or beta-carotene in research done at Harvard Medical School. Plus, a recent Creighton University study found that even though post-menopausal women who took vitamin D and calcium supplements for five years had a lower risk of developing cancer, there wasn’t a big enough difference to be statistically significant. In other words, it might have just been a coincidence.
Myth: Hey, it can't hurt
The old thinking went something like this—sure, vitamin pills might not help you, but they can't hurt either. However, a series of large-scale studies has turned this thinking on its head, says Demetrius Albanes, MD, a nutritional epidemiologist at the National Cancer Institute. (Don't miss these other 55 health myths that won't go away.) The shift started with a big study of beta-carotene pills. It was meant to test whether the antioxidant could prevent lung cancer, but researchers instead detected surprising increases in lung cancer and deaths among male smokers who took the supplement. No one knew what to make of the result at first, but further studies have shown it wasn't a fluke—there's a real possibility that in some circumstances, antioxidant pills could actually promote cancer (in women as well as in men). For instance, a more recent 10-year study looking at more than 77,000 adults over 50 found that vitamin B6 and B12 supplements increased lung cancer risk for men (though not for women). Other studies have raised concerns that taking high doses of folic acid could raise the risk of colon cancer. (Learn more about supplements that increase your risk of cancer.) Still others suggest a connection between high doses of some vitamins and heart disease. Vitamins are safe when you get them in food, but in pill form, they can act more like a drug, Albanes says—with the potential for unexpected and sometimes dangerous effects.