"Between 1986 and 1991, 29,584 persons took part in a randomized nutritional intervention trial in Linxian, China, an area whose residents had chronically low intakes of several nutrients and high rates of esophageal and gastric cancer as well as stroke. Using a one-half replicate of a 2(4) factorial design, we randomized individuals to one of eight groups which received combinations of four supplements: retinol and zinc (factor A), riboflavin and niacin (factor B), vitamin C and molybdenum (factor C), and beta-carotene, alpha-tocopherol (vitamin E), and selenium (factor D). Deaths that occurred during 5 years of supplementation were ascertained and classified according to cause. At the end of the supplementation period, we measured blood pressure readings and determined the prevalence of hypertension. Participants who received factor D had reductions in total mortality (9%) and total cancer mortality (13%)."

(International Epidemiology Institute, Rockville, MD. Vitamin/mineral supplementation and cancer risk: international chemoprevention trials. Proceedings of the Society for Experimental Biology an Medicine, 1997; Nov., 216(2):291-6)