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Thyroid hormones play an important role in body homeostasis by facilitating metabolism of lipids and glucose, regulating metabolic adaptations, responding to changes in energy intake, and controlling thermogenesis. Proper metabolism and action of these hormones requires the participation of various nutrients. Among them is zinc, whose interaction with thyroid hormones is complex. It is known to regulate both the synthesis and mechanism of action of these hormones. In the present review, we aim to shed light on the regulatory effects of zinc on thyroid hormones. Scientific evidence shows that zinc plays a key role in the metabolism of thyroid hormones, specifically by regulating deiodinases enzymes activity, thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH) synthesis, as well as by modulating the structures of essential transcription factors involved in the synthesis of thyroid hormones. Serum concentrations of zinc also appear to influence the levels of serum T3, T4 and TSH. In addition, studies have shown that Zinc transporters (ZnTs) are present in the hypothalamus, pituitary and thyroid, but their functions remain unknown. Therefore, it is important to further investigate the roles of zinc in regulation of thyroid hormones metabolism, and their importance in the treatment of several diseases associated with thyroid gland dysfunction.

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ABSTRACT In recent years, there has been growing interest in clarifying the pathogenesis of some chronic diseases, such as obesity and type 2 diabetes mellitus. Metabolic alterations in these diseases are characterized by chronic hyperglycemia and insulin resistance. Studies have demonstrated the participation of minerals in the pathogenesis of insulin resistance, more specifically their involvement in the synthesis and regulation of insulin. Selenium is an anti-inflammatory and antioxidant micronutrient that is essential for the activity of selenoproteins. Two selenoproteins (glutathione peroxidase and selenoprotein P) are known to be involved in the insulin signaling pathway. The aim of this review is to provide an update on the role of selenium in insulin resistance mechanisms. Evidence shows that adequate concentrations of selenium play a key role in the secretion and action of insulin, but an excess of selenium in the body is associated with the pathogenesis of insulin resistance and the development of diabetes mellitus.

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OBJECTIVE: This review aims to bring updated information on the relationship between oxidative stress and the role of selenium as antioxidant nutrient in mechanisms involved in the pathogenesis of type 2 diabetes mellitus. Data source: The bibliographic survey was conducted in PubMed, SciELO and Lilacs, considering the 2002-2014 period, and included the following types of studies: randomized or quasi-randomized controlled trials, cohort, case-control study, case series and case report. Forty-nine pertinent scientific studies were selected. Data synthesis: Several studies have demonstrated the contribution of acute and/or chronic hyperglycemia to the manifestation of oxidative stress in type 2 diabetic patients. Accordingly, selenium has an important participation in controlling this disease due to its antioxidant role in the elimination of free radicals, present in excess, and because it blocks the activation of nuclear transcription factor kappa B, a regulator sensitive to oxidants that stimulates the production of inflammatory mediators (cytokines) and adhesion molecules. CONCLUSIONS: There is convincing experimental evidence demonstrating the involvement of selenium in glycemic control. However, current information is still scarce and inconsistent, and it is necessary to conduct further studies on the subject to determine the selenium intake safety range as well as clarify the influence of this mineral on the manifestation of type 2 diabetes mellitus and its associated disorders

OBJETIVO: Esta revisão visa trazer informações atualizadas sobre a relação entre o estresse oxidativo e o papel do selênio como nutriente antioxidante em mecanismos envolvidos na patogênese do diabetes mellitus tipo 2. Fonte de dados: O levantamento bibliográfico foi realizado nas bases de dados Pubmed, SciELO e Lilacs considerando o período de 2002 a 2014 e abrangeu os seguintes tipos de estudos: ensaios clínicos controlados randomizados ou quase-randomizados, coorte, estudo caso-controle, série de casos e relato de caso. Foram selecionados 49 que se relacionavam com esta pesquisa bibliográfica. Síntese dos dados: Várias pesquisas têm demonstrado a contribuição do estado hiperglicêmico agudo e/ou crônico na manifestação do estresse oxidativo em pacientes diabéticos tipo 2. Nesse sentido, o selênio possui participação importante no controle dessa doença, devido ao seu papel antioxidante na eliminação dos radicais livres, presentes em excesso, e por bloquear a ativação do fator de transcrição nuclear kappa B, um regulador sensível a oxidantes que estimula a produção de mediadores inflamatórios (citocinas) e de moléculas de adesão. CONCLUSÕES: Existem evidências experimentais convincentes que demonstram a participação do selênio no controle glicêmico. No entanto, as informações atuais ainda são bastante escassas e inconsistentes e faz-se necessária a realização de novos estudos sobre o tema a fim de determinar a faixa de segurança de ingestão de selênio, além de obter esclarecimentos acerca da influência do mineral sobre a manifestação do diabetes mellitus tipo 2 e das desordens a ele associadas

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