According to the findings of the SELECT trial (The Selenium and Vitamin E Cancer Prevention Trial) published in the 12th October 2011 issue of JAMA (Journal of the American Medical Association), vitamin E supplementation of 400 IU per day may carry a 17% increased risk for prostate cancer.

The study began in 2001 and followed 35,533 healthy men aged 50 years or older (black men) or 55 years or older (all others) in 427 study sites in the United States, Canada, and Puerto Rico. The men were randomly split into four equal-sized groups, first one receiving selenium only (200 μg/d from L-selenomethionine), second one vitamin E only (400 IU/d of all-rac-alpha-tocopheryl acetate), third one received both agents, and last one received placebo. All participants had a prostate-specific antigen level of 4.0 ng/mL or less, and a digital rectal examination not suspicious for prostate cancer.

These results contradict earlier findings by an Alpha-Tocopherol, Beta-Carotene trial conducted in Finland, which primarily investigated the two supplements in relation to lung cancer and heart disease risk, but unexpectedly found a 40% decrease in prostate cancer incidence.

Initial SELECT results published in 2008 found 1758 cases of prostate cancer, with the greatest number (473) in the vitamin E group (hazard ratio [HR], 1.13), 432 in the selenium group (HR, 1.04), 437 in the selenium plus vitamin E group (HR, 1.05), and 416 in the placebo group (HR, 1.0).

Following this review, the use of supplements was stopped by the Data and Safety Monitoring Committee in October 2008. In order to determine any longer term benefit or harm the study participants were followed for 3 additional years.

The latest results, which are based on data collected up to 5th July 2011, include 521 additional cases of prostate cancer and confirm the initial findings with 147 of these new cases in the vitamin E group (HR, 1.17; P = .008), 143 in the selenium group, 118 in the combination group, and 113 in the placebo group.

The study also found a non-significant increased risk for type 2 diabetes mellitus in the selenium group (P = .34), but failed to show either benefit or harm in relation to lung, colorectal, total other cancers, deaths and grade 4 cardiovascular events.