January 2017
Mara Ventura, Miguel Melo, and Francisco Carrilho
Abstract
Introduction. Selenium is a micronutrient embedded in several proteins. In adults, the thyroid is the organ with the highest amount of selenium per gram of tissue. Selenium levels in the body depend on the characteristics of the population and its diet, geographic area, and soil composition. In the thyroid, selenium is required for the antioxidant function and for the metabolism of thyroid hormones.
Methods. We performed a review of the literature on selenium's role in thyroid function using PubMed/MEDLINE.
Results. Regarding thyroid pathology, selenium intake has been particularly associated with autoimmune disorders. The literature suggests that selenium supplementation of patients with autoimmune thyroiditis is associated with a reduction in antithyroperoxidase antibody levels, improved thyroid ultrasound features, and improved quality of life. Selenium supplementation in Graves' orbitopathy is associated with an improvement of quality of life and eye involvement, as well as delayed progression of ocular disorders. The organic form of selenium seems to be the preferable formulation for supplementation or treatment.
Conclusion. Maintaining a physiological concentration of selenium is a prerequisite to prevent thyroid disease and preserve overall health. Supplementation with the organic form is more effective, and patients with autoimmune thyroiditis seem to have benefits in immunological mechanisms. Selenium supplementation proved to be clinically beneficial in patients with mild to moderate Graves' orbitopathy.
Conclusions
The maintenance of a physiological concentration of selenium (selenostasis) through a balanced diet or, alternatively, via supplementation is a prerequisite not only to prevent thyroid disease but also to maintain overall health. Selenium has a U-shaped relationship with disease, and either the deficiency or the excess of this micronutrient may be associated with adverse outcomes. In fact, there is a selenium concentration range in the body in which selenium benefits seem to be maximized.
Selenium supplementation in patients with Hashimoto's thyroiditis and reduced intake of this micronutrient may be useful, even for those who are already being treated with levothyroxine, although further studies are needed to confirm this benefit.
In patients with mild to moderate Graves' orbitopathy, selenium supplementation seems to be beneficial and the organic formula (selenomethionine) seems to be more advantageous than the inorganic formula.
