This review covers current knowledge of
selenium in the environment, dietary intakes, metabolism and status, functions in the body,
thyroid hormone metabolism,
antioxidant defense systems and oxidative metabolism, and the immune system.
Selenium toxicity and links between deficiency and
Keshan disease and
Kashin-Beck disease are described. The relationships between
selenium intake/status and various health outcomes, in particular gastrointestinal and
prostate cancer,
cardiovascular disease, diabetes, and male fertility, are reviewed, and recent developments in genetics of
selenoproteins are outlined. The rationale behind current dietary reference intakes of
selenium is explained, and examples of differences between countries and/or expert bodies are given. Throughout the review, gaps in knowledge and research requirements are identified. More research is needed to improve our understanding of
selenium metabolism and requirements for optimal health. Functions of the majority of the
selenoproteins await characterization, the mechanism of absorption has yet to be identified, measures of status need to be developed, and effects of genotype on metabolism require further investigation. The relationships between
selenium intake/status and health, or risk of disease, are complex but require elucidation to inform clinical practice, to refine dietary recommendations, and to develop effective public health policies.