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According to a new study, researchers discovered that taking vitamin E or selenium supplements could increase a man's risk of prostate cancer. The researchers reported that the risk depends greatly on how much selenium is already present in the body.

"No one's ever been able to demonstrate any benefit for taking high doses of selenium or vitamin E, so why do it?" lead author Dr. Alan Kristal, associate head of the Cancer Prevention Program at the Fred Hutchinson Cancer Research Center in Seattle, said. "There's no benefit, there's only risk, so what's the point?"

Kristal and colleagues examined data that was collected from the Selenium and Vitamin E Cancer Prevention Trial (SELECT), which was funded by the U.S. National Cancer Institute. The study started in 1991 and the goal was to find any evidence that taking supplements could be beneficial for prostate cancer.

The participants were divided into different groups and took 200 micrograms of selenium or 400 IU of vitamin E or a combination of both. A control group did not take any of the supplements. The researchers discovered that taking selenium and vitamin E had a negative effect on men's health. The study, which was supposed to last 12 years, was ended in 2008.

"The levels they were giving these men in the study are much higher than would be found in most multivitamins and higher than the daily recommended allowance," said Dr. Durado Brooks, director of prostate and colorectal cancers for the American Cancer Society according to WebMD.

The researchers then looked at the data once again to see if the selenium levels already present in the body played a factor in prostate cancer risk. They measured selenium levels via toenail samples. The researchers compared 1,739 men within the SELECT trial that were diagnosed with prostate cancer to a cancer-free control group of 3,117 men. The participants were all matched in race and age. The team discovered that for men who already had high levels of selenium, their prostate cancer risk increased by 91 percent if they took the supplements.

For men who had low selenium levels but were taking vitamin E supplements, their risk of prostate cancer rose by 63 percent and their risk of aggressive cancer increased by 111 percent. The researchers concluded that even though the dose of selenium and vitamin E were higher in the study, men should avoid taking these supplements in general.

The study was published in the Journal of the National Cancer Institute.