Vitamin E May Increase Risk of Prostate Cancer

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Adding to the evidence that regularly taking dietary supplements may do more harm than good, researchers at the Cleveland Clinic have found that men taking vitamin E are not protected from prostate cancer, and may even be at higher risk for disease, compared with men not using the supplements.

The new study is only the latest blow to E, a popular supplement that has been touted as a powerful way to prevent everything from prostate and breast cancer to heart disease, vision loss and Alzheimer’s. In recent years, however, in-depth studies have broken vitamin E’s healthy spell, finding that people who take it are no better off than people who don’t.

Still, based on animal studies and early population studies, scientists had believe that vitamin E supplementation could be a smart and inexpensive way to prevent prostate tumors, given that the vitamin’s antioxidant effects may combat potentially damaging changes to the DNA in prostate cells.

“This finding was surprising, because all the evidence previously suggested that vitamin E may be protective against prostate cancer,” says the Cleveland Clinic’s Dr. Eric Klein, lead author of the new study published in the Journal of the American Medical Association.

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The current study is a follow-up to one of the first rigorous studies of the effects of vitamin E and selenium on prostate cancer risk, published by Klein and colleagues in 2008. That study, in which men were randomly assigned to take either supplement, or both together, or a placebo, Klein and his team found no difference in cancer risk among any of the groups, suggesting that vitamin E offered no protective anticancer benefit. Based on those results, the study was stopped. Additional analysis revealed that vitamin E may even boost risk of developing tumors.

To further understand what was going on, Klein continued the study with the majority of participants, who had stopped taking supplements but had agreed to continue providing information on their prostate cancer status for an additional 18 months.

In that time, Klein and his team found that even after the men had stopped taking vitamin E, their risk of prostate cancer remained higher than that of men who had originally been assigned a placebo. “The effect seemed to continue even after the supplements stopped,” he says, suggesting that vitamins have powerful effects on body systems that may have lasting consequences. “People have to get out of the idea that taking vitamins is innocuous, and that their effects stop when they stop taking them.”

Klein doesn’t know exactly how vitamin E may increase the risk of prostate, but is hoping that his biobank of tissue samples from participants in the trial, which contains their starting levels of vitamin E and selenium, might provide some clues. By accounting for these baseline levels of the vitamin, he or others hope to determine whether it’s vitamin E itself, or whether it’s the dose of the vitamin, that may be contributing to prostate cancer. For example, people who are deficient in vitamin E may be able to take supplements safely and may even benefit from some anticancer effect, while those who are already getting enough of the vitamin may, by taking extra doses, trigger some as-yet unknown mechanism that prompts prostate cancer cells to grow abnormally.

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So, it’s still possible that vitamin E supplements may help prevent some disease. So far, the most promising results are with Alzheimer’s patients. In some studies, people with early signs of dementia show slower rates of cognitive decline if they take vitamin E than if they don’t. But even here, the evidence isn’t strong enough for doctors to recommend that those on the road to Alzheimer’s take E to ward off their disease.

Overall, it seems, the growing consensus is that unless you need supplements to treat a specific deficiency, nutrients and vitamins are best obtained through a healthy diet. And that goes for E as well, says Klein, since it won’t help you avoid cancer. “There doesn’t seem to be much benefit to taking vitamin E if you are otherwise healthy,” says Klein.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.