For Debate: When is Selenium Deficiency Suspected and When is Its Measurement Indicated?

Selenium (Se) is an essential trace element involved in numerous biological processes including the antioxidant defense system and thyroid hormone metabolism. Since the content of Se in the body is highly dependent on that in the environment, Se deficiency rarely occurs in individuals living in areas rich in Se; with the exception of preterm infants and patients nourished exclusively with parenteral and enteral nutrition (PN and EN) without Se supplementation. Severe Se deficiency causes increases in T4 levels associated with decreases in T3 levels due to the blockage of the conversion of T4 to T3.