According to the results of two large randomized studies, selenium and vitamin E supplements do not reduce the risk of prostate cancer. These results were published in early online publications in the Journal of the American Medical Association on December 9, 2008.

Other than skin cancer, prostate cancer is the most commonly diagnosed cancer in U.S. men. In 2008 there were expected to be more than 186,000 new diagnoses of prostate cancer and more than 28,000 deaths from the disease. Previous studies suggested the risk of developing prostate cancer was reduced among men receiving selenium supplements or vitamin E supplements.

To further explore the relationship between selenium and vitamin E supplementation and prostate cancer risk, researchers conducted two large randomized trials.

The first trial, known as SELECT (the Selenium and Vitamin E Cancer Prevention Trial), enrolled more than 35,000 men from the United States, Canada, and Puerto Rico. Eligible participants were African American men age 50 or older and other males aged 55 or older. At the start of the study (2001-2004), 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:

1. Selenium supplementation
2. Vitamin E supplementation
3. Selenium and vitamin E supplementation
4. Placebo

Study participants have now been followed for over five years, and men in the selenium and/or vitamin E groups do not have lower rates of prostate cancer than men in the placebo group. The hazard ratios (HRs) were as follows:

1. Selenium: 1.04
2. Vitamin E:1.13
3. Selenium and Vitamin E:1.05
4. Placebo:1.00

The second trial, the Physicians’ Health Study II (PHS II), enrolled more than 14,000 U.S. male physicians 50 years of age or older. These data were also presented at the American Association for Cancer Research’s Seventh Annual International Conference in Washington, D.C. on November 16, 2008. This trial assessed vitamin E and vitamin C supplementation, as well as supplementation with a multivitamin and beta-carotene. The current analysis focuses on the vitamin E and vitamin C results.

Study participants in PHS II have now been followed for an average of eight years, during which 1,008 prostate cancers were detected. Almost 2,000 total cancers were detected during the study period. Neither vitamin E nor vitamin C influenced the risk of prostate cancer. The incidences of prostate cancer for the various groups were observed:

1. Placebo: 17.8 cases per 1,000 person years
2. Vitamin E:17.3 cases per 1,000 person years
3. Vitamin C:17.6 cases per 1,000 person years

These authors also reported that vitamin C and vitamin E had no effect on colorectal, lung, or other cancers.

Comments: These results confirm other studies suggesting that vitamin E does not prevent cancer. (In fact, some studies have suggested harm from vitamin E supplementation). The SELECT trial is the first to document the ineffectiveness of selenium in preventing prostate cancer. The Physicians’ Health Study II is the first to document the ineffectiveness of vitamin E and C in preventing prostate cancer. These data are at odds with studies showing that lower serum levels of vitamin E and selenium are associated with an increased risk for some cancers. One possible explanation is that artificial supplementation is not as effective as consuming antioxidants in food.