Selenium is an essential trace mineral, and its role in thyroid health is well-documented in scientific literature. The thyroid gland contains more selenium by weight than any other organ in the body. Selenium is a crucial component of the enzymes known as iodothyronine deiodinases, which convert thyroxine (T4) to the more active triiodothyronine (T3). These enzymes also help protect the thyroid gland from oxidative damage during hormone synthesis, as selenium is a cofactor for glutathione peroxidase, a key antioxidant enzyme.

Numerous clinical studies and systematic reviews have shown that selenium supplementation can reduce thyroid peroxidase (TPO) antibodies in individuals with autoimmune thyroiditis (Hashimoto’s disease), though effects on thyroid hormone levels and clinical outcomes are less consistent. The European Thyroid Association recommends considering selenium supplementation in some thyroid conditions, particularly autoimmune thyroiditis, but notes that benefits are modest and more research is needed for definitive guidance.

Selenium picolinate is one of several forms of selenium available as a supplement; while the bulk of research is on selenomethionine or sodium selenite, selenium picolinate is assumed to have similar bioavailability. Overall, there is scientific evidence supporting the use of selenium (including picolinate forms) to support thyroid health, particularly in the context of autoimmune thyroid conditions.