Vitamin E increases prostate cancer risk: Study

Vitamin E supplements increase the risk of prostate cancer in healthy, middle-aged and older men, according to research published today that strengthens the evidence that some micronutrients, often marketed as antioxidants, are ineffective at preventing cancer and might even do harm.

Men who took 400 international units (IUs) of vitamin E daily – much more than you’d typically find in a multivitamin -- had higher rates prostate cancer than did men who took a placebo, according to the research, an updated review of the Selenium and Vitamin E Cancer Prevention Trial, or SELECT.

“Supplements are widely used in the absence of evidence they do any good,” said Howard Parnes, chief of the prostate research group at the National Cancer Institute and a co-author of the paper published in the Journal of the American Medical Association.

"This should be a wake-up call for people taking lots of over-the-counter supplements on the basis of what may seem to be a good idea,” Parnes said. “Anything that has biological activity could have an ill effect, as well as a beneficial one.”

Adding to concern for men, the study follows a new U.S. Preventive Services Task Force recommendation that the PSA blood test should no longer be part of routine screening for prostate cancer because the test may cause unnecessary harm. 

The antioxidant vitamin boom began back in the early 1990s when scientists noticed that people who eat foods rich in antioxidants, often found in fruits and vegetables, have lower rates of cancer and heart disease.

Antioxidants, researchers suspect, play a key role by protecting DNA from damage caused by free radicals, which are unstable and potentially damaging molecules.

The results of antioxidant trials in humans, however, have been largely disappointing, as I reported in "Radical thinking on antioxidants."

Earlier research suggesting that selenium or vitamin E might reduce the risk of developing prostate cancer provided the impetus for the SELECT study.

But the study, which began in 2001 and included over 35,000 men, was halted in 2010 because it was clear that neither vitamin E, selenium, nor a combination of the two were reducing cancer. It also showed a worrisome trend of more prostate cancers in those who were taking only vitamin E.

After the use of supplements ended, the researchers continued monitoring the health of more than half the participants via mail questionnaires. The follow-up results showed 17 percent more cases of prostate cancer in those who took vitamin E supplements, a statistically significant difference, the researchers said.

The Council for Responsible Nutrition, the leading trade association representing the dietary supplement industry, said it is risky to examine a nutrient in isolation.

It pointed out that the JAMA study also had a hopeful, albeit confusing, finding: Vitamin E didn’t appear to increase prostate cancer risk when it was combined with selenium, though selenium alone was not shown to be helpful. Moreover, the participants who took vitamin E didn’t show an increase in any other form of cancer or higher rates of cardiovascular disease or diabetes.

“This reinforces the theory that vitamins work synergistically and that drug-like trials of nutrients, when used in isolation from other nutrients, may not be the most appropriate way to study them,” Duffy MacKay, the council’s vice president of scientific and regulatory affairs, said in a statement.

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