The main effects of selenium on human health are protection of cardiovascular and myocardial health, enhancement of immunity, antioxidant, and improvement of visual dysfunction. 1. Protecting cardiovascular and myocardial health: selenium has a protective effect on human cardiomyocytes and can reduce the probability of cardiovascular disease. If the selenium deficiency in the human body, it will lead to myocardial fiber necrosis, myocardial small arteries and capillary damage. 2. Enhance immunity: selenium can up-regulate interleukin-2 receptor expression, which can increase the activity of lymphocytes, NK cells, lymphokine-activated killer cells, and thus improve the body’s immunity. 3. Antioxidant: selenium can eliminate lipid peroxides in the body and prevent other free radicals from damaging the body. 4. Improvement of visual dysfunction: A related study found that regular selenium supplementation can improve visual dysfunction, if selenium deficiency can cause neurological visual impairment. Selenium has other effects. However, the human body ingested or inhaled too much selenium, there may be dizziness, diarrhea, nausea, chest tightness, shortness of breath, and other adverse symptoms, and can lead to a decrease in serum calcium levels, and so on. Selenium deficient people are recommended to take selenium supplements under the guidance of a doctor, not blindly.