Vitamin E, vitamin C, or selenium may not lower the risk of prostate cancer

The Selenium and Vitamin E Cancer Prevention Trial (SELECT) randomly assigned over 35,000 men to receive daily selenium, vitamin E, both, or placebo. After almost five and a half years, no significant differences were observed between any of the groups in relation to prostate cancer risk.

In the second study – the Physicians' Health Study II – about 15,000 men were randomly assigned to vitamin E supplements every other day and daily vitamin C supplements. Over the eight tears of follow-up no effects on either prostate cancer or overall cancer.

The results are to be published in the 7th January 2009 issue of the Journal of the American Medical Association (JAMA).

Researchers for the Physician's Health Stuudy led by J. Michael Gaziano, MD, from Brigham and Women's Hospital, recruited 14,641 male physicians in the US, and randomly assigned them to receive supplements of 400 IU of vitamin E every other day, or 500 mg of vitamin C daily, or placebo for about eight years. Neither vitamin had any effect on the incidence of prostate cancer or total cancer.

In a challenge to the results, Gaziano and his co-workers said: “It is reassuring that there was not a clear signal of harm for either agent.”

Commenting on the limitations, the researchers said: “The study was conducted in a well-nourished population, and thus, these results may not preclude potential benefits in less well-nourished populations.

“One concern is the choice of dose used. It is not feasible to test multiple doses in these large-scale trials. The doses of vitamin E and C in the PHS were chosen because they were in the range of those commonly in use, because they did not have known major adverse effects that would impact adherence, and because their safety data were sound - a critical issue when conducting a trial by mail.

“The form of vitamin E chosen for our study was synthetic alpha-tocopherol, the most abundant component of natural vitamin E. However, in nature, vitamin E is composed of both alpha- and gamma-tocopherol. Gamma-Tocopherol has been postulated to possibly play a more important role in prostate cancer protection,” they added.

Bonnie - eureka! The researchers finally wised up to the critical errors in structuring these studies. In particular, using synthetic vitamin E, all alpha tocopherol, renders the study useless. I am glad the researchers owned up to it.