The results of a large, randomized trial suggest that taking daily vitamin E supplements may increase a man’s risk of prostate cancer. These results were published in the Journal of the American Medical Association.
Prostate cancer is the most commonly diagnosed type of cancer (other than skin cancer) in US men. Although many prostate cancers are diagnosed at an early, curable stage, treatment of prostate cancer can cause urinary, sexual, and bowel problems that have a substantial impact on quality of life. Prevention of prostate cancer, therefore, continues to be an important research priority.
There is a great deal of interest in the relationship between diet and cancer, and some previous studies suggested that selenium and vitamin E may reduce the risk of certain types of cancer, including prostate cancer.
To further explore the relationship between selenium and vitamin E supplementation and risk of prostate cancer, researchers conducted a randomized trial known as SELECT (the Selenium and Vitamin E Cancer Prevention Trial). The study enrolled more than 35,000 men from the United States, Canada, and Puerto Rico. At the start of the study, all the men had normal prostate-specific antigen (PSA) levels and a normal digital rectal examination.
Study participants were assigned to one of four groups:
- Selenium supplementation (200 micrograms per day)
- Vitamin E supplementation (400 IU per day)
- Selenium and vitamin E supplementation
An initial report from this study (based on roughly five years of follow-up) found that risk of prostate cancer was higher in the vitamin E group than in the placebo group; this result did not meet the criteria for statistical significance, however, suggesting that it could have occurred by chance alone. Nevertheless, because the results indicated that it was very unlikely that either vitamin E or selenium would provide a benefit, study participants were told to stop taking the supplements.
Although study participants stopped using the supplements in 2008, researchers continue to collect information from them. At the time of the current analysis, men had been followed for a minimum of 7 years.
- Men in the placebo group had the fewest prostate cancers. Prostate cancer was diagnosed in 529 men in the placebo group, 620 men in the vitamin E group, 575 men in the selenium group, and 555 men in the selenium plus vitamin D group.
- Men in the vitamin E group were 17% more likely than men in the placebo group to be diagnosed with prostate cancer. This result was statistically significant (unlikely to be due to chance alone). The differences between the other study groups and the placebo group were not statistically significant.
These results suggest that daily vitamin E supplements may increase the risk of prostate cancer among healthy men. The researchers recommend that consumers be skeptical of health claims for unregulated over-the-counter products unless there’s strong evidence of a benefit from clinical trials.
 Lippman SM, Klein EA, Goodman PJ et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers. The Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009; 301:39-51.