WASHINGTON (Reuters) - Selenium and vitamin E supplements do not prevent prostate cancer and may in fact be a little bit dangerous, US researchers reported on Monday.

The study of 35,000 men showed the supplements did not work together or alone to prevent prostate cancer, the most common type of cancer in men in the United States.

"As we continue to monitor the health of these 35,000 men, this information may help us understand why two nutrients that showed strong initial evidence to be able to prevent prostate cancer did not do so," Dr. Eric Klein of the Cleveland Clinic in Ohio, who worked on the study, said in a statement.

Other, earlier studies had suggested that the two supplements might prevent prostate cancer. Both are antioxidants — compounds that interfere with chemical reactions that can damage cells and DNA.

The National Cancer Institute, which helped organise the study, said men taking part are being told to stop taking the supplements they had been given but will continue to have their health monitored for about three more years.

"The data also showed two concerning, but not statistically significant, trends: there were slightly more cases of prostate cancer in men taking only vitamin E and slightly more cases of diabetes in men taking only selenium," the NCI, one of he National Institutes of Health, said in a statement.