Selenium is naturally found in some foods, added to others, and sold as a supplement. Selenium is a constituent of more than two dozen selenoproteins that play crucial roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection.
Selenium is inorganic (selenate and selenite) and organic (selenomethionine and selenocysteine). Both are selenium-rich foods . Inorganic selenites and selenates in soils are converted by plants into selenocysteine, selenomethionine, and their methylated derivatives.
Most selenium occurs in animal and human tissues as selenomethionine, which can be absorbed into proteins nonspecifically. Muscle stores 28% to 46% of the body’s selenium. Selenocysteine and selenite are reduced to hydrogen selenide, which is transformed to selenophosphate for selenoprotein production.
Plasma and serum selenium concentrations measure selenium status. Blood and urine concentrations reflect selenium intake. Long-term selenium consumption can be monitored by analysing hair or nail selenium levels. Quantification of selenoproteins (such as glutathione peroxidase and selenoprotein P) also measures selenium level. Healthy persons need 8 mcg/dL or more plasma or serum selenium for selenoprotein production.