Selenium supplementation reduces levels of thyroid autoantibodies in individuals with autoimmune thyroid disease.

Study: Selenium supplementation in the management of thyroid autoimmunity during pregnancy: results of the “SERENA study”, a randomized, double-blind, placebo-controlled trial

This study found that pregnant women who took selenium supplements had lower levels of harmful thyroid antibodies after giving birth, while those who took a placebo had higher levels. So yes, selenium seems to help reduce these antibodies in people with thyroid autoimmunity.

Study: Effect of selenium on thyroid autoimmunity and regulatory T cells in patients with Hashimoto’s thyroiditis: A prospective randomized‐controlled trial

This study found that taking selenium supplements helped lower harmful antibodies in people with Hashimoto’s thyroiditis, a common autoimmune thyroid condition. It’s like selenium helps calm down the immune system’s mistaken attack on the thyroid.

Study: Challenges and perspectives of selenium supplementation in Graves’ disease and orbitopathy

This study found that taking selenium supplements might help lower harmful antibodies in people with an autoimmune thyroid problem, especially in mild cases, though more research is still needed.

Study: Effects of Selenium Supplementation on Graves' Disease: A Systematic Review and Meta-Analysis

This study found that taking selenium supplements helped lower harmful antibodies in the thyroid of people with Graves' disease, at least for a few months. So yes, selenium seems to help reduce these antibodies.