Over the last century, our understanding of selenium has progressed considerably and we have come to recognize it as an essential component or cofactor of enzymes throughout metabolism, such as glutathione peroxidase (GPx), thioredoxine reductase and iodine deiodinase. GPx acts against hydrogen peroxide and lipid peroxidation and is an important line of defense against free radicals; thioredoxine reductase is involved in nucleus redox status; and iodine deiodinase is involved in thyroid hormone metabolism, which is frequently impaired in critically ill patients. Selenium also has an anticarcinogenic effect that is thought to be induced by the production of methyselenol, a selenometabolite that affects gene expression and modifies cell cycling and immune function. We review current knowledge concerning clinically relevant selenoproteins, discuss the potential role of these compounds in health and disease, review the epidemiology of selenium deficiency and its clinical implications with a special emphasis on critically ill patients and discuss the role of selenium supplementation in critical care settings.
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