Selenium status and supplementation in thyroid disorders: A narrative review of current evidence

Selenium (Se), an essential trace element, plays a pivotal role in thyroid hormone synthesis and antioxidant defence mechanisms. This narrative review comprehensively examines the current evidence on Se status and supplementation in various thyroid disorders. Numerous studies indicate that Se deficiency may contribute to the development and progression of thyroid diseases, particularly autoimmune conditions such as Graves' disease (GD), Graves' orbitopathy (GO), and autoimmune thyroiditis (AIT), including Hashimoto's thyroiditis (HT). In GD and GO, Se supplementation, especially when combined with methimazole, has been shown to enhance hormone normalization and antioxidant capacity, although results vary across studies. In AIT and HT, consistent reductions in thyroid autoantibodies and inflammatory markers have been observed following Se supplementation, particularly with selenomethionine. However, the evidence remains inconsistent regarding Se's impact on hypothyroidism, pregnancy-related thyroid dysfunction, goitre, and thyroid cancer. Supplementation of Se has been associated with improvements in quality of life in some thyroid disorders such as GD, GO and HT with subclinical hypothyroidism. While some studies suggest a potential protective or modulatory role, findings vary by geographic region, baseline Se status, and study designs. Excessive intake of Se may also carry risks of toxicity (selenosis) and should be approached with caution. In conclusion, Se supplementation offers potential therapeutic benefits, particularly in autoimmune thyroid diseases. However, further well-designed randomized-controlled trials are necessary to define the optimal form, dose, and duration of supplementation and to clarify its role across diverse thyroid conditions.