NOW Foods Selenium 100 mcg provides this essential trace mineral as selenium from selenomethionine — the organic, yeast-free form with the highest bioavailability and tissue retention of any selenium form. Selenium is an essential component of over 25 selenoprotein enzymes, including the glutathione peroxidase family (the body's primary antioxidant defense system), thioredoxin reductase, and iodothyronine deiodinase — the enzyme that converts inactive T4 thyroid hormone to the active T3 form. Adequate selenium is critical for thyroid function, immune defense, reproductive health, and protection against oxidative damage throughout the body. Research also shows selenium's role in reducing cancer risk at adequate intake levels. At 100 mcg, this provides the daily recommended intake in a clean tablet format. Manufactured in NOW's GMP-certified facility.