Selenium belongs to a kind of semi-metal, since 1973 the United Nations Health Organization will be selenium as the human body essential trace elements, selenium deficiency is very harmful to the human body, may cause cancer, cardiovascular disease, diabetes and so on. 1. Cancer: Some tumor epidemiological studies at home and abroad have shown that low selenium is one of the risk factors for tumor development, and the incidence of tumors in many regions of the world is negatively correlated with the concentration of selenium in the blood, and selenium can inhibit the occurrence and development of many tumors, such as colon cancer and hepatocellular carcinoma. 2. Cardiovascular disease: selenium is closely related to cardiovascular structure, function, disease occurrence and prevention, selenium deficiency may lead to increased incidence of coronary heart disease and hypertension. 3. Diabetes mellitus: the main change of pancreatic islet damage caused by selenium deficiency is the abnormality of the structure and function of β-cells as the main body, selenium has a certain protective effect on the oxidation of pancreatic islets caused by streptozotocin, so selenium deficiency is easy to suffer from diabetes mellitus. Selenium supplementation of the human body mainly by food intake to obtain, eat a moderate amount of selenium-containing food, can be very good to improve the problem of selenium deficiency, such as broccoli, garlic and other foods, such as every 100g of garlic is rich in 14.2 micrograms of selenium.