Although people commonly take vitamin E to boost their body's immune system and selenium to avoid heart disease, men have been warned to stop taking vitamin E and selenium supplements because researchers have found that overdose of vitamin E and selenium could dramatically raise a man's risk of prostate cancer.
In the study published in the Journal of the National Cancer Institute Feb. 21, researchers analyzed data from the Selenium and Vitamin E Cancer Prevention Trial, which began in 2001. The trial, which involved 35,000 men, sought to determine if taking high doses of vitamin E and selenium supplements could protect men from prostate cancer.
The trial, however, was scrapped as early as 2008 because researchers found that selenium has no benefit at all and vitamin E even put men more at risk of prostate cancer. A follow-up comparison of 1,739 of trial participants who were diagnosed with prostate cancer with more than 3,000 matched cancer-free men highlighted the risks of taking vitamin E and selenium supplements.
"But we found there's no benefit for anyone," said study author Alan Kristal, a faculty member in the Public Health Sciences Division at Fred Hutchinson Cancer Research Center in Seattle. "All we did find was a heightened risk. I'm now willing to go on the record and say that there is no evidence that high doses of supplements of anything are good for you."
The researchers also found that while selenium supplements do not have effect on men who started out lacking the mineral, they were harmful when taken by those who already have high selenium status at the start of the study, increasing risks of high grade cancer by 91 percent.
Vitamin E supplements were also found to increase the risk of prostate cancer in men with low selenium status by 63 percent. Risk for high-grade cancer is likewise increased by 111 percent.
"These supplements are popular - especially vitamin E - although so far no large, well-designed and well-conducted study has shown any benefits for preventing major chronic disease," Kristal said. "Men using these supplements should stop, period. Neither selenium nor vitamin E supplementation confers any known benefits, only risks."
Kristal said the study showed the implications and risks of consuming high-dose dietary supplements.
"Many people think that dietary supplements are helpful or at the least innocuous. This is not true," he said. "We know from several other studies that some high-dose dietary supplements -- that is, supplements that provide far more than the daily recommended intakes of micronutrients -- increase cancer risk. We knew this based on randomized, controlled, double-blinded studies for folate and beta carotene, and now we know it for vitamin E and selenium. Men using these supplements should stop, period. Neither selenium nor vitamin E supplementation confers any known benefits -- only risks. "