Vitamins seem like such a good thing that drugstores have whole aisles devoted to them, including products that promise a healthy prostate.
Those concoctions often contain hefty doses of vitamin E, because some studies have suggested that this darling of antioxidant enthusiasts prevents prostate cancer. But now the largest study to ask head-on if that's true has come up with a surprising answer: Daily vitamin E supplements may actually raise a man's risk of prostate cancer.
"The practical implication," says Dr. Ian Thompson, a study author, "is that a man should go to his medicine cabinet and look to see if he's taking a vitamin E supplement and very seriously consider whether he should continue taking it."
Even if he's not taking a separate daily dose of vitamin E, it's probably in his daily multivitamin pill, often far in excess of the recommended daily allowance of 22.4 International Units. The new study, which appears in this week's JAMA, Journal of the American Medical Association, randomly assigned men to 400 IUs a day of vitamin E or a placebo. That's a typical dose in vitamin E supplements.
The study also tested the effect of selenium on prostate cancer risk, since other research had suggested a benefit. The researchers found none.
The study is persuasive, because it involved nearly 36,000 men in 427 North American locations, who were monitored for seven years. "It's not a fluke," Thompson says.
Those who were taking vitamin E were told to stop about three years ago when the investigators found the supplements weren't likely to do any good. The researchers say the increased risk of prostate cancer continued to rise even after men stopped taking the vitamin. They're following participants to see if the risk will continue to go up.
Even if the risk peaks at 17 percent, Thompson says that's a lot. "In the context of 2 million men being diagnosed every decade with prostate cancer, 17 percent has enormous impact," says the cancer specialist, who's based at the University of Texas Health Science Center in San Antonio.
Thompson says the magnitude of the risk was a surprise.
He and his colleagues have no idea why vitamin E should be linked to a higher risk of prostate cancer. In 1994 a Finnish study that was designed to see if vitamin E would lower the risk of lung cancer in smokers found, incidentally, about a 25 percent reduction in prostate cancer among those who took the vitamin.
When the current vitamin E and selenium study was launched a decade ago, many thought both substances might protect against a bunch of diseases — including heart trouble, Alzheimer's and cancer.
But the bloom is off that rose. "For vitamin E, the only thing I'm aware of that it might be good for — in combination with a number of other antioxidants — are certain eye disorders," Thompson says. "Every other time vitamin E has been looked at in large-scale trials, it hasn't had any effect."
He points out that researchers once had high hopes that beta-carotene, a vitamin A precursor that is fat-soluble like vitamin E, might prevent lung cancer. But like vitamin E and prostate cancer, it had the opposite effect.
Curiously, the new study found that men who took both vitamin E and selenium didn't have as high a risk of prostate cancer as those who took vitamin E alone. "I have no idea why," Thompson says.
The overall lesson, once again, is that the best way to get vitamins and other micronutrients is probably in the produce department at your local grocery store, rather than in pill form.
Thompson isn't disappointed in the outcome of the study. "Some people look at this and say, 'Doggone, you had a negative study, it didn't work and in fact, you showed that something people often times take can cause harm,' " he says. "I look at it as saying, my goodness, over the next decade there will be men who won't have prostate cancer because of this observation."
Imagine, he says, if the number of prostate cancer diagnoses could be cut by 20,000 or 30,000 a year simply by telling men not to take vitamin E. "That's really a remarkable opportunity," he says.