Selenium supplementation, including forms such as selenium picolinate, has been studied for its potential benefits in autoimmune thyroid diseases like Hashimoto's thyroiditis. Several clinical trials and meta-analyses suggest that selenium supplementation can reduce thyroid peroxidase antibody (TPOAb) levels in patients with Hashimoto's, which is considered a marker of reduced autoimmune activity. A 2016 meta-analysis (Winther KH et al., Thyroid, 2016) concluded that selenium supplementation for 3-6 months significantly reduced TPOAb levels in patients with Hashimoto’s, though the effect on thyroid function and clinical symptoms is less clear. The European Thyroid Association has endorsed the potential benefit of selenium supplementation in mild cases, particularly in regions with low selenium status, but the American Thyroid Association has not made such recommendations due to inconsistent clinical benefits.

Most studies use selenium in the form of selenomethionine or sodium selenite, but selenium picolinate is assumed to provide similar bioavailable selenium. The evidence supporting selenium’s use is not robust enough to recommend it for all patients with Hashimoto's, but it is stronger than purely traditional or anecdotal use. Importantly, long-term safety data is limited, and excessive selenium intake can be harmful. Therefore, selenium supplementation may be considered as an adjunct in selected cases, but it is not a primary treatment. More research is needed to determine optimal dosing, duration, and patient selection.