Hello Gladys Bone, Thank you for posting your query in HGM Selenium is an anti oxidant and is required for the proper activity of a group of enzymes called glutathione peroxidases. These enzymes play a key role in the body s detoxification system and they also provide protection against the damaging effects of free oxygen radicals. In addition to the activity of glutathione peroxidase, selenium-containing enzymes are involved in recycling of vitamin C from its spent form back to its active one, allowing for greater antioxidant protection. A selenium-containing enzyme is responsible for transforming a less active thyroid hormone called T4 into the more active T3. Selenium is normally present in sea foods especially Tuna and Shrimps, nuts, grains, beef and poultry. If you take these in your diet then additional Selinium may not be required. If you have further queries you would find me on the HCM website. Wish you good health. Dr. Noble Zachariah