Thyrotropin Levels, Insulin Resistance, and Metabolic Syndrome: A Cross-Sectional Analysis in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).

Abstract

Previous studies have described an association with thyrotropin (TSH) levels, insulin resistance, and metabolic syndrome. We performed a cross-sectional analysis to investigate the relationship between TSH levels, insulin resistance, and metabolic syndrome using baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). Diabetics and individuals using medications that interfere in thyroid function were excluded, leaving 10,935 participants (54.3% women) for current analyses. Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) values above the 75th percentile was considered as indicative of presence of insulin resistance. Logistic regression models were built using HOMA-IR and metabolic syndrome as the dependent variable, and quintiles of TSH as the independent variable (first quintile as reference). Odds ratios (OR) were presented with multivariate adjustment for socioeconomic/cardiovascular risk factors for insulin resistance, and adjustment only for socioeconomic factors and smoking for metabolic syndrome. Age, body mass index, waist measurement, fasting glucose and fasting and post load insulin and HOMA-IR increased according to TSH quintiles. Subjects in the fifth TSH quintile presented an OR of association with insulin resistance of 1.86 [95% confidence interval (95% CI) 1.26-2.75], regardless of gender. For the metabolic syndrome, subjects in the fifth quintile presented an OR of 1.21 (95% CI 1.01-1.45) and remained positive only for men (OR 1.37; 95% CI 1.07-1.76). Restricting the analysis to quintiles of TSH in the normal range did not change the results. In this cross-sectional evaluation, high TSH quintiles were associated to insulin resistance/metabolic syndrome.