Definition

The amino acid methionine with selenium substituting for the sulphur moiety. Methionine is an essential amino acid in humans, whereas selenium is a free-radical scavenging anti-oxidant, essential for the protection of various tissues from the damages of lipid peroxidation. As a trace mineral that is toxic in high doses, selenium is a cofactor for glutathione peroxidase, an anti-oxidant enzyme that neutralizes hydrogen peroxide. L-selenomethionine is considered a safe, efficacious form of selenium and is readily bioavailable. Selenium may be chemoprotective for certain cancers, particularly prostate cancer.