Supplements Don't Lower Prostate Cancer Risk

(January 7, 2009) - For the second time a study has found that vitamin and mineral supplements (Read about "Vitamins & Minerals") do not lower the risk of developing prostate cancer. (Read about "The Prostate") In perhaps the largest cancer chemoprevention trial ever conducted, researchers have found that supplementation with vitamin E or selenium, alone or in combination, was not associated with a lower risk of prostate cancer or other cancers. (Read about "Cancer: What It Is") The previous study found that vitamin C and E had no impact. Both studies are being published in the Journal of the American Medical Association.

The number of prostate cancer deaths in the United States has declined in recent years, but this cancer remains one of the most common malignancies in U.S. men, with approximately 186,000 new cases and 29,000 deaths (the second leading cause of cancer death) estimated for 2008. An effective prevention strategy for prostate cancer would have substantial public health benefits, according to background information. Previous studies have indicated the potential of selenium and vitamin E for preventing prostate cancer.

Researchers designed the study to examine the effects of selenium and vitamin E, alone or in combination, on the risk of prostate cancer and other health outcomes in relatively healthy men. The trial included 35,533 men, age 50 years or older for African-American men and age 55 years or older for other men at the start of the study, from the U.S., Canada, and Puerto Rico. The participants were randomly assigned to receive one of four interventions over 3 years:

• selenium (200 µg/day)
• vitamin E (400 IU/day)
• selenium and vitamin E
• placebo

The plan was to follow everyone for a minimum of 7 years. The study however was halted early, after about five and half years, when the results showed no benefits.

The researchers found that there were no statistically significant differences in the absolute numbers (or 5-year incidence rates) of prostate cancer diagnoses between the four groups: placebo, 416 cases (5-year rate of 4.43 percent); selenium, 432 cases (4.56 percent); vitamin E, 473 cases (4.93 percent); selenium + vitamin E, 437 cases (4.56 percent). There were nonsignificant increased risks of prostate cancer in the vitamin E group and type 2 diabetes mellitus (Read about "Diabetes") in the selenium group, but not in the selenium and vitamin E group.