The National Cancer Institute has announced its decision to suspend a study on the benefits of vitamin E and selenium supplements treatments on prostate cancer prevention. The study, called SELECT (Selenium and vitamin E Cancer Prevention Trial), involved more than 35,000 men and was conducted at 400 sites around the United States.

Researchers found a higher risk for aggressive prostate cancer in participants taking only vitamin E and a small increased risk of developing diabetes in subjects taking only selenium. The researchers cautioned that those effects may have been due to chance and they were not statistically significant.

Contrary to other studies that have shown that selenium and vitamin E supplements, both antioxidants, might decrease the risk of prostate cancer by 60% and 30%, respectively, the findings of this study were a major disappointment to those that had hoped that these supplements might prove to be some powerful anti-cancer agents.

The participants were randomly assigned to take either vitamin E (400 milligrams) and selenium (200 micrograms), vitamin E and placebo, selenium and placebo, or placebos alone. They didn’t know which nutrients they’d been assigned to take.

The 114 million-dollars study was conducted by U.S. National Cancer Institute.

“I am afraid it will be the end of the story for large trials of vitamin E and selenium to prevent prostate cancer,” said the study investigator Edward M. Messing, professor and chairman of urology and deputy director of the Cancer Center at the University of Rochester.

The researchers will continue to monitor the health of the participants for three more years. They were supposed to take the supplements for seven years. “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. He also said he believes it “highly unlikely” that the supplements will ultimately prove to have harmful effects.

An earlier study (of a much smaller group) conducted on the effect of selenium supplementation on the recurrence of skin cancers did not demonstrate a reduced rate of recurrence of skin cancers, but did show a reduced occurrence of total cancers.

In other studies, researchers are exploring whether some plant based substances, or drugs including the anabolic steroid toremifene, the enlarged-prostate treatment dutasteride, and finasteride might cut the risk of prostate cancer for men. Other studies found that beta-carotene supplementation failed to prevent lung cancer.

Prostate cancer is the ninth most common cancer worldwide, but the most common type of cancer in U.S. males. Prostate cancer screening for men aged 75 or older should be stopped, since the risks involved pose more immediate danger that the cancer itself. It seems that this type of cancer affected 18% of United States men and led to death of 3% in 2005 only. Prostate cancer is the fifth most deadly tumour after lung, breast, colon and pancreatic cancer.