The Physicians' Health Study II was a randomized, double-blind, placebo-controlled, factorial trial that began in 1997 and ended in 2011. It was designed to test four supplements -- (1) alternate-day vitamin E (400 international units of synthetic alpha-tocopherol) or its placebo; (2) daily vitamin C (500 mg synthetic ascorbic acid) or its placebo; (3) a daily multivitamin (Centrum Silver) or its placebo; and (4) alternate-day beta carotene (50 mg Lurotin) or its placebo -- in the prevention of cancer, cardiovascular disease, eye disease, and early cognitive decline among 14,641 male physicians aged 50 years or older. Participants were randomly assigned in a 2x2x2x2 factorial trial to receive combinations of the four active supplements or their placebos. Pills and/or packaging were provided by BASF Corporation, Pfizer (formerly Wyeth, American Home Products, and Lederle), and DSM Nutritional Products (formerly Roche Vitamins).