Most vitamin E supplements are merely alpha tocopherol. Last month I ran an article that showed that the gamma tocopherol form of vitamin E was likely more important in preventing cancer. The current issue of American Jounnal of Clinical Nutrition has further proof that gamma tocopherol may actually be superior to alpha tocopherol in the prevention of Alzheimer's Disease. The researchers speculate that this may explain explain the absence of vitamin E protection against Alzheimer's Disease reported in some previous studies with the use of vitamin E supplements as they have traditionally contained only (alpha)-tocopherol.
So bottom line: Be sure and check to see that your vitamin E supplement has gamma tocopherol.
American Journal of Clinical Nutrition February 2005 Vol 81(2) 508-514