In 1996 researchers at the Arizona Cancer Center discovered that selenium supplementation decreases the risk of developing cancer by 40% and reduces the risk of dying from cancer by almost 50%. The benefits of selenium were ascribed to its ability to scavenge DNA-damaging free radicals and to help in the elimination of damaged, potentially cancerous cells. Researchers at the Indiana University have now discovered a third possible mode by which selenium might fight cancer. They discovered that selenomethionine, the primary organic form of selenium, turns on a key regulatory protein, p53, which is one of the body's main initiators of DNA repair. Previous research has shown that people who have an efficient DNA repair mechanism are less likely to develop cancer. Eating more selenium-rich foods, such as Brazil nuts, or supplementing with 200 micrograms/day of selenium may help people improve the efficiency of their DNA repair mechanism. A daily intake of 200 micrograms has been found to be entirely safe.
Longtin, Robert. Selenium for prevention: Eating your way to better DNA repair? Journal of the National Cancer Institute, Vol. 95, January 15, 2003, pp. 98-100