Relationship between Thyroid-Stimulating Hormone and Insulin in Euthyroid Obese Men

Abstract

Background/Aims: Obesity has been associated with hypothyroidism and impaired insulin sensitivity. However, few studies have specifically addressed the association between insulin sensitivity and thyroid function. Our aim was to look for a relation between these 2 factors in a sample of obese males. Methods: One hundred and forty-four euthyroid male obese patients – mean age 42.6 years, mean body mass index (BMI) 41.8 – were enrolled in this cross-sectional study. The hospital study protocol at entrance included baseline serum thyroid-stimulating hormone (TSH), insulin and glucose concentrations. Data were studied using an age-adjusted simple and multivariate linear regression analysis with TSH as the dependent and insulin and BMI as the independent variables. Results: Mean TSH and insulin were 1.6 and 21.2 mU/l, respectively. It was found that their relationship follows a regression model: TSH = 1.725–0.019 (age) + 0.003 (insulin) + 0.017 (BMI). Further data showed a positive correlation between BMI and TSH (r = 0.22; p < 0.05), as well as between serum baseline insulin (>10 mU/l) and TSH concentration (r = 0.27; p < 0.05). This association was stronger in patients with higher insulin values (>21.2 mU/l; r = 0.40; p < 0.01). However, negative correlations between age and insulin (r = –0.14; not significant) and age and TSH (r = –0.35; p < 0.05) were observed. Conclusions: In obese males, insulin resistance is significantly related with impairment of thyroid function, and this situation seems to be attenuated with age.