Selenium is a trace mineral that is essential for human health. Selenium, in the form of selenoproteins, is an indispensable component in the normal functioning of the body, and their role is the synthesis of the active form of thyroid hormones and the regulation of the cell cycle, and thus manifests the function of selenium in our body. However, the most important action of selenoproteins is their antioxidant action. Selenium is found in unrefined foods, especially in wholemeal flour, seafood, egg yolk, fish, grains and their products, and meat and meat products, and the highest content is found in Brazil nuts. There is a moderate to high health risk if too much selenium is ingested although selenium poisoning is very rare. The intake of selenium in the diet is a reflection of the concentration of selenium in the soil on which the plant grows, or the concentration of selenium in the food that the animals eat. Selenium deficiency is rare and can adversely affect the antioxidant activity of selenoproteins.