Selenium yeast is a form of the essential trace mineral selenium, bound organically in yeast cells, and is commonly used to support thyroid health. Scientific evidence supports its use for this purpose. Selenium is a cofactor for several selenoproteins, including the enzymes iodothyronine deiodinases, which are crucial for the activation and deactivation of thyroid hormones (conversion of thyroxine/T4 to the more active triiodothyronine/T3). Additionally, selenium-dependent glutathione peroxidases help protect the thyroid gland from oxidative damage during hormone synthesis, as the thyroid has one of the highest concentrations of selenium in the body.

Clinical studies have shown that selenium supplementation can benefit individuals with autoimmune thyroid conditions such as Hashimoto’s thyroiditis and Graves’ disease. For example, several randomized controlled trials (RCTs) and meta-analyses have reported that selenium supplementation (often as selenium yeast) can reduce thyroid peroxidase antibody (TPOAb) levels and may improve overall thyroid function and well-being in patients with Hashimoto’s thyroiditis. However, the effects on clinical outcomes (such as improved thyroid hormone levels or remission rates) are less robust, and not all studies find benefit.

Overall, selenium yeast is scientifically validated for supporting thyroid function, especially in populations with low selenium status, but its use should be guided by clinical need as excess selenium can be toxic.