Selenium and vitamin E supplements failed to prevent prostate cancer – this was the conclusion of the largest clinical trial of this kind, called “SELECT,” or Selenium and Vitamin E Cancer Prevention Trial. The study of 35,000 men showed that prostate cancer patients taking vitamin E at doses used in the trial had a small increase in prostate cancer, while men taking only selenium were more likely to develop diabetes.

Participants were divided into four groups: one group took 200 micrograms of selenium and 400 ICU vitamin E, the second group received the selenium and a vitamin E placebo, the third group got vitamin E with a selenium placebo and the fourth took placebos of both supplements. The participants didn't know which nutrients they'd been assigned to take, or if they were in the placebo group.

The supplements failed to prevent prostate cancer - and study’s authors noted two worrisome trends: patients taking vitamin E alone had a slightly higher rate of prostate cancer, while patients who took selenium alone were more likely to develop diabetes. Researchers have said the trends were not statistically significant and they may just be due to chance.

“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, co-author of the study, said in a statement.

As a result, the National Cancer Institute, that helped organize the study, said men taking part in the trial should stop taking the supplements. They will continue to have their health monitored for three more years.

The authors of the study called the findings about these supplements “disappointing.” Dr. Eric Klein says he believes it “highly unlikely” that the supplements will prove to have harmful effects.

Other studies, however, have shown that men taking high levels of multivitamins along with other supplements have increased risk of advanced or fatal prostate cancer. The study found that men who took multivitamins more than seven times a week (they were classed as excessive vitamin users) had a significantly higher risk of advanced and fatal prostate cancers (32 and 98 per cent respectively) compared with men who did not take multivitamins at all.

Prostate cancer is the most common type of cancer in men in the United States. It affects about 186,000 Americans and almost 28,000 men loose the battle with the disease each year. Prostate cancer is the fifth most deadly tumour after lung, breast, colon and pancreatic cancer.

Prostate cancer screening for men aged 75 or older should be stopped, since the risks involved pose more immediate danger that the cancer itself. The stress that is caused by the procedure, as well as the risks involved by the biopsies that are required to confirm the disease pose a much greater threat to that person.