The 2009 SELECT (Selenium and Vitamin E Cancer Prevention Trial) study prospectively randomized over 35,000 men into 4 groups: selenium (200 μg/day) with matching placebo; vitamin E (400 IU/day) with matching placebo; both agents; or placebo. This study was halted due to lack of efficacy for risk reduction with no potential for benefit. While preliminary evaluation revealed essentially non-significant data, the safety monitoring committee expressed concern regarding an increased risk of prostate cancer in the group receiving vitamin E close to statistical significance, and a non-significant increased risk of type 2 diabetes mellitus in the selenium plus placebo group.
Following the initial trial, observation continued, with each group having greater than 13,000 person-years of follow-up. There were 521 additional cases of prostate cancer detected since the original study was published. The hazard ratio in the group of men given vitamin E who developed prostate cancer was 1.17; that for the selenium group was 1.09; that for the group who received vitamin E plus selenium was 1.05. The authors concluded absolute increased risks of prostate cancer per 1000 person-years of 1.6 for the vitamin E group; 0.8 for the selenium group; and 0.4 for the group who received both vitamin E and selenium.
Detection and prevention of prostate cancer remains an important public health goal on the worldwide level. The authors noted that these results differ from previous studies on the relationship between vitamin E supplementation and prostate cancer risk. The ATBC (Alpha-Tocopherol, Beta Carotene) trial reported a 35% risk reduction in men who took 50mg/day of vitamin E over an average period of 6.1 years. The reported 17% increased risk of prostate cancer in the SELECT trial follow-up suggests not only the potential for harm through vitamin E supplementation, but as the authors also claim, there is a great need for consumers to be surveillant of the potential health benefit claims of unregulated over-the-counter products that may claim to be beneficial to overall health and cancer prevention.
Klein EA, Thompson IM, Tangen CM, et al. Vitamin E and the risk of prostate cancer. JAMA 2011;306(14):1549-56.