Named after Selene, Greek goddess of the moon, selenium (Se) has moved has moved from being thought of as a toxicant to being considered an essential nutrient with the potential to reduce cancer risk in the span of seven decades. Diversity of Selenium Functions in Health and Disease focuses on current knowledge of aspects of Se research relevant to its medical use, and particularly to chemoprevention of cancer. It covers how Se is integrated into selenoproteins, selenium compounds with individual functions and dual functions, and unexpected links to Se such as with diabetes. The text ends with a discussion of polymorphisms and mutations in genes of selenoproteins. The chapters elucidate why studies undertaken to prevent diseases with selenium ended with disappointing outcomes and often with the opposite result, i.e. disease promotion. They show that benefit, failure, or side effects depend on: The chemical form and dose of selenium The selenium status of the individual ingesting selenium The capacity of selenium form to serve as a source for selenoprotein biosynthesis The function of selenoproteins reacting to a change in the selenium status The stage of the disease (mainly cancer) at the time point of intervention The genetic background of individuals to be treated Bringing together the accumulated evidence regarding selenium biochemistry, the book covers aspects not found in available general monographs. The narrow focus on medical uses of Se helps resolve the present confusion about potential benefits and hazards of selenium in human health. The book gives you a solid scientific basis for optimum use of selenium in preventing or treating human diseases and answering the questions: Why is selenium essential? How much is required? What are the health consequences of low selenium and can selenium reduce cancer risk?