New studies show that the popular supplement may increase the risk of cancer.

by Melinda Wenner Moyer

If you’ve been taking vitamin E because you heard it helps prevent prostate cancer or heart disease, you may want to stop. The supplement — taken in some form by almost 40 percent of all American men — was shown by a long-term study funded by the National Cancer Institute to increase the incidence of prostate cancer by an alarming 17 percent.

Vitamin E is essential to human health; without the fat-soluble nutrient, your body wouldn’t function properly. The nutrient may improve immune function and dilate blood vessels, which can help prevent the blood clots that lead to heart attacks. It’s also a known antioxidant, meaning it should supposedly help mop up cancer-causing free radicals. For this reason, some experts have suggested that older men take a large dose of vitamin E daily to help prevent prostate cancer. Trial participants took 400 IU per day, which is nearly 20 times more than the FDA’s daily recommendation for the nutrient. But, “lots of men in this age group — over 50 — buy these supplements at the doses that we used and take them,” says trial co-author Dr. Eric Klein, a urologist at the Cleveland Clinic.

So how could it be that vitamin E increases cancer risk? One possibility, says Klein, is that when people take too much vitamin E, their bodies aren’t able to absorb other cancer-fighting vitamins. Still another theory is that vitamin E somehow spurs budding cancer cells to grow, literally “feeding the tumor,” says Dr. Lisa Ganjhu, a gastroenterologist and internist at St. Luke’s–Roosevelt Hospital in New York City.

It’s not just vitamin E that has come under scrutiny, though — recent studies have called the safety of many vitamin supplements into question. A 2007 analysis of 68 clinical trials published in the Journal of the American Medical Association reported that beta-carotene, vitamin A, and vitamin E supplements can increase a person’s risk of premature death by 5 percent. A 2009 trial of nearly 7,000 men found that taking folate and vitamin B12 pills increases cancer risk in people with heart disease. And a large trial funded by the National Cancer Institute discovered that beta-carotene and vitamin A supplements increase the risk of fatal lung cancer in smokers.

None of this research means that you should swear off all vitamins. “For the average healthy guy with a reasonable diet, I recommend about 1,000 IU of vitamin D whenever daily sun exposure is not happening, as well as one gram of an omega-3 oil supplement from algae or krill,” says Dr. David Katz, founder of Yale University’s Prevention Research Center. But, he adds, “it’s important to remember: supplement, not substitute. There is nothing in a pill that can replace eating well.”