Prostate Cancer Risk and Vitamin E

To the Editor: The observation by Dr Klein and colleagues¹ that treatment with 400 IU/d of α-tocopherol increased the incidence of prostate cancer might be explained by α-tocopherol inducing the depletion of γ-tocopherol. α-Tocopherol is 1 of the 4 forms of vitamin E that occur naturally in food (α-, β-, γ-, and δ-tocopherol). Treatment with large doses of α-tocopherol reduces serum concentrations of γ-tocopherol, thereby upsetting the natural balance of vitamin E isomers in the body.² Both α- and γ-tocopherol have been found to inhibit the growth of human prostate cancer cells in vitro, but γ-tocopherol was more potent.³ In a case-control study of 10 456 men, higher blood levels of α-tocopherol and γ-tocopherol were each associated with a lower risk of developing prostate cancer, but the association with γ-tocopherol was stronger than that of α-tocopherol.⁴ In a randomized controlled trial, treatment with a relatively small dose of α-tocopherol (50 IU/d) significantly decreased the incidence of prostate cancer in a group of cigarette smokers.⁵