Selenium is an essential trace element that is indispensable for the function of numerous enzymes, particularly antioxidant enzyme systems such as glutathione peroxidase. It supports the defense against cell damage caused by free radicals and plays a key role in thyroid function, especially in the conversion of thyroxine (T4) into the active triiodothyronine (T3).

A selenium deficiency can contribute to increased susceptibility to infections, thyroid dysfunction, muscle weakness, and cardiovascular diseases. A low selenium level is also observed in inflammatory diseases and autoimmune disorders.