Selenium is an essential trace mineral that is important for many bodily processes, including cognitive function, a healthy immune system, and fertility in both men and women. It contributes to thyroid hormone metabolism and DNA synthesis, and it helps protect against oxidative damage and infection, according to the United States Office of Dietary Supplements.

Selenium is also a cofactor in the synthesis of glutathione peroxidases. This enzyme provides free radical scavenging properties, including support for healthy cells and a healthy immune response to internal challenges. Selenium also supports detoxification in a healthy liver, and may support pregnant women and new mothers. It is present in human tissue, mostly in skeletal muscle. Dietary sources are varied. They include Brazil nuts, seafood, and meats. The amount of selenium in food often depends on the selenium concentration of the soil and water where farmers grew or raised the food.