WASHINGTON, Oct. 13 (Xinhua) -- In a trial that included about 35,000 men, those who were randomized to receive daily supplementation with vitamin E had a significantly increased risk of prostate cancer, according to a study published this week in the Journal of the American Medical Association.

The study followed more than 35,533 men 50 or older at 427 sites in the United States, Canada and Puerto Rico. The men were divided into four groups who took daily doses of 400 international units of Vitamin E and 200 micrograms of selenium; Vitamin E and a placebo that looked like selenium; selenium and a placebo that looked like Vitamin E; or two placebos. The recommended daily intake of Vitamin E is about 22.4 international units.

The researchers from the Cleveland Clinic found that the rate of prostate cancer detection was greater in all treatment groups when compared with placebo but was statistically significant only in the vitamin E alone group -- a 17 percent increased rate of prostate cancer detection. The difference in rates of prostate cancer between vitamin E and placebo became apparent during the participants' third year in the trial. The elevated risk estimate for vitamin E was consistent across both low- and high-grade disease.

"The observed 17 percent increase in prostate cancer incidence demonstrates the potential for seemingly innocuous yet biologically active substances such as vitamins to cause harm. The lack of benefit from dietary supplementation with vitamin E or other agents with respect to preventing common health conditions and cancers or improving overall survival, and their potential harm, underscore the need for consumers to be skeptical of health claims for unregulated over-the-counter products in the absence of strong evidence of benefit demonstrated in clinical trials," the researchers said.