Selenium and the thyroid
A review on the role of selenium and its interaction with iodine and iron that together contribute to adequate thyroid hormone status.
This article provides an update on the role of the essential trace element selenium and its interaction with the other trace elements iodine and iron that together contribute to adequate thyroid hormone status. Synthesis, secretion, metabolism and action of thyroid hormone in target tissues depend on a balanced nutritional availability or supplementation of these elements. Selenium status is altered in benign and malignant thyroid diseases and various selenium compounds have been used to prevent or treat widespread diseases such as goiter, autoimmune thyroid disease or thyroid cancer. Several studies, most with still too low numbers of cases, indicate that selenium administration in both autoimmune thyroiditis (Hashimoto thyroiditis) and mild Graves’ disease improves clinical scores and well-being of patients and reduces thyroperoxidase antibody titers. However, published results are still conflicting depending on basal selenium status, dose, time and form of selenium used for intervention. Evidence for sex-specific selenium action, lack of beneficial effects in pregnancy and contribution of genetic polymorphisms (selenoprotein S) has been presented. Adequate nutritional supply of selenium that saturates expression of circulating selenoprotein P, together with optimal iodine and iron intake, is required for a healthy and functional thyroid during development, adolescence, adulthood and aging.
Selenium compounds and selenoproteins protect the thyroid gland from H2O2 and ROS damage. Thyroid hormone synthesis and metabolism represent a remarkable example of coevolution of biology and function of three essential trace elements: iodine, selenium and iron. Many studies, primarily of women, have shown that adequate selenium status benefits thyroid-related diseases. Low selenium status is observed in patients with newly diagnosed Graves’ disease and autoimmune thyroiditis. The possible mechanisms of action of selenoproteins in benign and malignant thyroid disease, and the action of selenocompounds in thyrocytes, endothelial cells, angiofollicular units and/or immune cells remain to be established. Nutritional, environmental, genetic, life-phase and disease-related factors modulate the fine-tuned interaction between the three trace elements, selenium, iodine and iron, thyroid function and thyroid hormone homeostasis and thus play an important role in maintenance of human health, prevention and treatment of diseases.