The use of vitamin E, vitamin C, beta carotene, and/or multivitamins may keep cancer, cardiovascular disease, eye diseases, or cognitive decline from occurring. This randomized clinical trial studied vitamin E, vitamin C, beta carotene, and/or multivitamins to see how well they work compared with placebos in preventing cancer, cardiovascular disease, eye disease, and cognitive decline in male doctors aged 50 years and older.