Selenium is an essential trace element in the human body, and selenium has antioxidant and heavy metal binding effects in the human body. Selenium deficiency in the human body may lead to hair loss, nail loss, and can even cause heart disease, hypothyroidism, immune dysfunction and other diseases. Selenium can not be synthesized by the body, can only be taken from outside, so the right amount of selenium supplementation is necessary. First, the role of selenium: first of all, selenium can synthesize glutathione peroxidase, thus scavenging free radicals and protecting cell membranes; secondly, selenium can synthesize selenoprotein in the body, which can combine heavy metals in the body through chelation reaction. Both of these effects are beneficial to health. Second, the benefits of selenium supplementation: because of the antioxidant effect of selenium, selenium supplementation can remove lipid peroxides in the blood to a certain extent, thus regulating blood lipids and preventing thrombosis; at the same time, because of the antioxidant effect, selenium supplementation can indirectly help control the development of chronic hepatitis, cirrhosis, gastric ulcer, diabetes, cataract and other diseases; in addition, selenium supplementation can also prevent Keshan disease, large bone disease, which are two kinds of deficiency In addition, selenium supplementation can also prevent two endemic diseases caused by selenium deficiency, such as Keshan disease and big bone disease. In addition, scientific selenium supplementation can also reduce the toxic side effects of tumor patients after radiotherapy to a certain extent. However, it is important to pay attention to the appropriate amount of selenium supplementation, as excessive selenium supplementation may cause selenium toxicity, so it is necessary to supplement selenium under the guidance of doctors.