In 1817, Jons Jacob Berzelius, a Swedish chemist, isolated selenium from a red powdery substance found at the bottom of lead chambers in a sulfuric acid plant and named it “Selenium”. For a long time afterward, selenium was regarded as a toxic element. Schwarz et al. were the first to recognize the biological functions of selenium, and Rotruck et al. later discovered that selenium is an essential component of glutathione peroxidase (GSHPX) and also a constituent of many proteins in animals. Selenium cannot be synthesized in animals and is therefore an essential nutrient for them. Selenium has the functions of promoting growth, protecting cardiovascular and myocardial health, alleviating the toxicity of heavy metals in the body, protecting the sound function and eyesight of visual organs, as well as providing antioxidant, antiviral, anti-cancer, anti-aging effects and enhancing immunity. Selenium deficiency can lead to impaired function of vital organs in the human body and decreased immunity; severe selenium deficiency may cause Keshan disease, Kashin-Beck disease, and arthritis. Appropriately increasing selenium intake is of great significance for preventing certain diseases and maintaining physical health.