Reviewers: Kenneth Blank, MD and John Han-Chih, MD
Source: Journal of the National Cancer Institute, Vol. 90, No. 6, March 18, 1998
Vitamins have long been studied for their presumed health benefits, including a possible role in the prevention of cancers. Three of the most commonly researched vitamins are Vitamin A, Vitamin E, and Beta Carotene.
Many natural and synthetic analogs of vitamin A exist and are collectively termed retinoids-- after Vitamin A's generic name, retinol. The retinoids function in the nucleus of the cell, effecting gene transcription. Vitamin E is an anti-oxidant and, as such, serves the important process of destroying dangerous free radicals in the cell. Free radicals are molecules that can damage the cell membrane and DNA. In addition Vitamin E may alter the function of protein kinase C- a protein important in cell proliferation. Exactly how beta-carotene effects cellular functions is more speculative. In vitro studies have shown beta-carotene to possess immune enhancing properties and its breakdown products are structurally similar to retinoids and therefore have may act on gene transcription.
The results of a large randomized prospective study examining the effects of Vitamin E and beta-carotene on prostate cancer were published in the March 18, 1998 issue of the Journal of the National Cancer Institute. Over 27,000 men from southwestern Finland were randomly assigned to take either alpha-tocopherol (a form of vitamin E), beta carotene, both vitamins or a placebo. All study participants were smokers between the ages of 50 and 69, and remained on the vitamins or placebo for 5-8 years. In total 246 new prostate cancers were diagnosed and 62 of the study participants died of prostate cancer. Data analysis revealed that those men who received alpha-tocopherol (alone or with beta carotene) had a significant decrease in the risk of developing palpable prostate cancer. Mortality from prostate cancer was 41% lower among men receiving alpha-tocopherol . In contrast, men receiving beta carotene had a increased risk- by almost 25%-of developing prostate cancer and an increase risk of dying from the their prostate cancer.
Other large studies examining the role of vitamins in preventing cancer have found conflicting results. A similar study as the one reported here using alpha-tocopherol and beta carotene to prevent lung cancer in smokers found neither vitamin had a protective effect . Tens of thousands of people were entered into either the beta-carotene and Retinol Efficacy Trial or the Physicians Health Study, neither of which found that supplementation with beta carotene protected against the onset of prostate cancer. And, in fact, the study reported here did not find that alpha-tocopherol or beta carotene effected the rate of development of latent prostate cancer, which defined as, not palpable on digital rectal exam. These conflicting results regarding the effect of vitamins on development of cancer lead the authors' of this paper to conclude that, " before vitamin E can be recommended for prostate cancer prevention, further clinical trials are needed."