Selenium is one of the essential trace elements and is a strong antioxidant with similar effects to vitamin E, but with greater potency. Selenium can be used to regulate the rate of redox reactions in the body, affect the metabolism and activity of certain important enzymes, and regulate the absorption and consumption of vitamins A, C, E and K in the body. Selenium is also an important component of glutathione peroxidase in the body, which has a protective effect on the structure of cell membranes and promotes the immunity of the body. Selenium deficiency is an important cause of Keshan disease. Selenium deficiency induces liver necrosis and selenium deficiency induces cardiovascular disease. In people with mild or moderate selenium deficiency, signs and symptoms are not obvious. Selenium is an important trace element for maintaining normal physiological functions of human body. Selenium is absorbed by the intestine after being ingested by the body and distributed in organs such as liver, spleen, kidney and heart. Selenium is combined with proteins and transported to tissues via blood, and selenium is involved in constituting glutathione peroxidase, which can catalyze the conversion of reduced glutathione into oxidized glutathione and prevent the damage of hydrogen peroxide and oxidized lipids to cells. Selenium deficiency is an important cause of Keshan disease. Selenium deficiency induces liver necrosis and selenium deficiency induces cardiovascular disease. In humans with mild or moderate selenium deficiency, signs and symptoms are not obvious. Selenium deficiency can cause leukodystrophy in animals, and there is a correlation between selenium in the human environment and the level of selenium load in humans and the onset of Keshan disease. Supplementation of a certain amount of selenium to the population in the disease area can reduce the incidence of Keshan disease. In addition selenium has been shown to have anti-carcinogenic effects against a variety of carcinogens in animal experiments. However, excessive amount of selenium can cause selenosis and hair loss and nail loss. The danger of selenium deficiency to women of childbearing age Selenium is an essential substance in the development of human embryo. Severe deficiency of selenium in women can lead to muscle atrophy and degeneration, thickening of limb joints, thinning of hair, weight loss, spinal deformation, cataract, etc. For women and children of childbearing age, selenium deficiency is likely to cause macrosomia and Creutzfeldt-Jakob disease. The incidence of cancer is also higher in low selenium areas and people with low blood selenium, such as the increased incidence of breast cancer, ovarian cancer and uterine cancer in women. Selenium deficiency in women of childbearing age makes it difficult to conceive; selenium deficiency in pregnant women makes them prone to miscarriage. Selenium deficiency affects the metabolism of thyroid hormones in the mother’s body and causes a decrease in the secretion of growth hormone, which in severe cases causes intrauterine developmental disorders in the fetus. How should selenium deficiency be prevented? Selenium deficiency can be supplemented by two ways: dietary supplementation and medicinal supplementation. The human body should be supplemented with selenium according to the results of the body’s trace elements test, following the principle of “how much selenium is lacking, no deficiency is not supplemented, food supplementation is the main, supplemented by medicine”. There are many ways to supplement selenium with food, animal organs, seafood, fish, eggs, meat, etc. are good sources of selenium, and eating more of these foods can safely and effectively supplement selenium. Moderate supplementation of trace elements selenium, consume foods rich in selenium, such as seafood, animal kidney, meat, rice, cereals, etc. Interventions such as applying selenium-fortified salt, promoting the consumption of selenium-rich foods, using sodium selenite for prophylactic dosing or fertilizing the soil with sodium selenite can all lead to a significant decrease in the incidence of Keshan disease and large joint disease. The Chinese medicine Astragalus contains rich selenium. It has a certain effect on the prevention and treatment of selenium deficiency. Foods that contain more selenium in daily life include seafood, meat (especially kidney of animals) and rice and cereals. Eggs contain more selenium than meat, for example, per 100 grams of food, pork contains 10.6 micrograms of selenium, eggs contain 23.3 micrograms of selenium, duck eggs contain 30.7 micrograms of selenium, goose eggs contain 33.6 micrograms of selenium, ginseng contains 15 micrograms of selenium and peanuts contain 13.7 micrograms of selenium. In addition to brewer’s yeast, wheat germ, garlic, asparagus, mushrooms and sesame, selenium-rich foods also include many seafood, such as prawns, tuna, sardines, etc. According to the observation of our adults daily food supplementation of selenium 25 micrograms or more has a health effect; selenium-deficient adults daily food supplementation of selenium 50 micrograms or 75 micrograms or more, taken continuously for 2 to 3 months, can correct selenium deficiency.