Selenium (Se) is an essential trace element in the human body and plays critical roles in a wide variety of physiological processes via selenoproteins. Selenoproteins (glutathione peroxidase, thioredoxin reductase, methionine sulfoxide reductase 1 and endoplasmic reticulum-selenoproteins, etc.) have antioxidant effects and are involved in regulating antioxidant activities. Importantly, glutathione peroxidase is primarily responsible for the antioxidant effects of selenoprotein.