Selenium is an essential trace element and component of a number of selenoproteins including glutathione peroxidase, which has a role in protecting against oxidative damage. Selenium is also known to play a role in immunocompetence. Blood selenium concentrations in newborns are lower than those of their mothers and lower still in preterm infants. In experimental animals low selenium concentrations appear to increase susceptibility to oxidative lung disease. In very preterm infants low selenium concentrations have been associated with an increased risk of chronic neonatal lung disease and retinopathy of prematurity.