Selenium is a trace element required by the body, with certain antioxidant, enhance physical fitness and other effects, can play a certain role in the prevention of immune system diseases, thyroid disease, cardiovascular disease, brain and nerve diseases, as well as reproductive system diseases: 1, prevention of immune system diseases: selenium can maintain the function of their own immune system, promote the body antibacterial, antiviral; 2, prevention of thyroid disease: thyroid gland. The deiodinase in the thyroid gland is selenoprotein, the thyroid gland contains high levels of selenium, and selenium plays an important role in the secretion of thyroid hormones; 3, prevention of cardiovascular diseases: research shows that the appropriate amount of selenium supplementation will reduce the total serum cholesterol and low-density cholesterol content, which plays a role in the prevention of cardiovascular diseases; 4, prevention of brain and nerve diseases: selenium plays an important role in the development of human brain tissue. If the lack of selenium elements are prone to irreversible damage to brain tissue. Research shows that selenoprotein has the function of scavenging reactive oxygen species, which can prevent the occurrence of neurodegenerative diseases to a certain extent; 5, prevention of reproductive system diseases: selenoprotein exists in the mitochondria of the sperm tail, due to its antioxidant effect, can protect sperm and help improve sperm vitality. In addition, some studies have shown that most patients with miscarriage and pre-eclampsia have low selenium levels in their bodies. Therefore, a moderate amount of selenium supplementation can prevent miscarriage and preeclampsia to some extent. It should be noted that there are many nutrients required by the body, and simply supplementing selenium while neglecting other aspects may also lead to other adverse consequences. The daily intake of selenium recommended by our nutrition society is 55 μg, and since the threshold of selenium in the body from beneficial to harmful is relatively close, it needs to be supplemented in moderate amounts. Too low or too high levels of selenium in the blood may lead to the occurrence of diseases, such as the appearance of nail loss, rough skin, eye diseases, abnormal liver function or induce the appearance of other diseases.