Selenium in the Treatment of Thyroid Diseases: An Element in Search of the Relevant Indications?

Abstract

responses to all 23 questions. The vast majority of specialists , of whom >90% were endocrinologists, had used Se, and around 25% of them often or always. Let's look into the thyroid phenotypes investigated [9]. Chronic Autoimmune Thyroiditis in Euthyroid Individuals While 3 out of 4 respondents (72%) thought that there was evidence supporting Se use, 79% prescribed it sometimes , often, or always. Half of those who prescribed Se (49%) did it prophylactically to prevent serum TSH increase (49%) or to decrease thyroid antibody levels (39%). However, trials among individuals not receiving levothy-roxine (LT 4) have not reported these effects [10]. 59% of the respondents advocated use of >100 μg Se daily, without having knowledge of the pretherapy Se levels. Importantly , the scientific societies do not recommend Se sup-plementation for this indication. Hypothyroidism, with or without TPOAb In case of subclinical hypothyroidism and positive TPOAb, 2 out of 3 respondents would (sometimes, often, or always) suggest use of Se. In case of negative TPOAb this propensity would decrease to 1 in 3 respondents. The Selenium (Se) deficiency has been associated with a number of diseases [1] , including thyroid diseases such as goiter, hypothyroidism, and autoimmune thyroiditis [2]. Se is an essential micronutrient that is incorporated into biologically active selenoproteins as the amino acid sele-nocysteine [3]. Among the most important are the iodo-thyronine deiodinases that are directly involved in thyroid hormone metabolism [3]. In healthy euthyroid individuals with marginal Se deficiency, Se supplementation has only minute, and clinically insignificant, effects on thyroid function [4]. However, Se levels have been found to be inversely correlated with thyroid size [5]. Furthermore, Se supplementation has been shown to decrease thyroid peroxidase antibodies (TPOAb) in autoimmune thyroid-itis [6, 7]. Accepting that chronic autoimmune thyroid diseases are multifactorial diseases, and that environmental triggers are key components in their etiology [8] , it is no surprise that Se deficiency has come into focus. It could be speculated that the above constitutes, in part, the inspiration for the massive use of Se, as revealed by an Italian questionnaire study focusing on the therapeutic use of Se in some well-characterized clinical situations [9]. Despite the inherent reservations in using such a questionnaire study, the survey seems to show that a number of specialists have adopted routine Se therapy in disease entities where the evidence is, to put it mildly, questionable. From a web-based survey of 1,888 Associazione Medi-ci Endocrinologi (AME) members, 778 (41%) provided