Dietary vitamin E linked to lower prostate cancer risk

Previous studies, including a clinical trial, have indicated that an increased intake of the antioxidant vitamin E may reduce the risk of the prostate cancer, but observational studies have reported conflicting results.

The new study, published in the journal Cancer Epidemiology Biomarkers & Prevention , adds significantly to the debate by reporting that dietary sources of the vitamin might reduce the risk of prostate cancer, but supplementary sources may not.

Over half a million new cases of prostate cancer are diagnosed every year world wide, and the cancer is the direct cause of over 200,000 deaths.

More worryingly, the incidence of the disease is increasing with a rise of 1.7 per cent over 15 years.

Lead author Margaret Wright from the National Cancer Institute, National Institutes of Health, and co-workers prospectively investigated if a link was observable between intakes of the four tocopherol forms of vitamin E and the risk of prostate cancer among 295,344 men, aged between 50 and 71, taking part in the NIH-AARP Diet and Health Study.

There are eight forms of vitamin E: four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta).

Alpha-tocopherol (alpha-Toc) is the main source found in supplements, and a European diet, while gamma-tocopherol (gamma-Toc) is the most common form in the American diet.

The subjects completed a questionnaire at the start of the study to quantify intakes of supplemental and dietary intakes of the four tocopherols.

During five years of follow-up, the researchers diagnosed 10,241 new cases of prostate cancer.

Regular intakes of vitamin E supplements ranging from zero to more than 800 International Units (IU) per day, was not associated with the risk of prostate cancer at any of the doses used.

On the other hand, Wright and co-workers calculated that dietary gamma-tocopherol was associated with a 32 per cent reduction in the risk of advanced prostate cancer.

"These results suggest that supplemental vitamin E does not protect against prostate cancer, but that increased consumption of gamma-tocopherol from foods is associated with a reduced risk of clinically relevant disease," wrote the researchers.

"The potential benefit of gamma-tocopherol for prostate cancer prevention deserves further attention," they concluded.

Previous research, including the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) trial, have proposed that the vitamin is thought to fight cancer through its antioxidant activity, which combats the oxidative stress involved in cancer development.

It also has other non-antioxidant properties, such as enhancement of the immune response, which may also play a role in the benefits seen.

The ATBC study, published in the New England Journal of Medicine (1994, Vol. 330, Issue 15, pp. 1029-35), reported that men taking a supplement of alpha-tocopherol (a form of vitamin E) had 32 per cent fewer cases of prostate cancer and a 41 per cent reduction in prostate cancer deaths.

Almost 30,000 male smokers were followed for up to eight years.

The European School of Oncology recommends eat a diet with a rich natural source of vitamin E. Source: Cancer Epidemiology Biomarkers & Prevention Volume 16, Pages 1128-1135, doi: 10.1158/1055-9965.EPI-06-1071 "Supplemental and Dietary Vitamin E Intakes and Risk of Prostate Cancer in a Large Prospective Study" Authors: M.E. Wright, S.J. Weinstein, K.A. Lawson, D. Albanes, A.F. Subar, L.B. Dixon, T. Mouw, A. Schatzkin and M.F. Leitzmann