Relationship between thyroid-stimulating hormone and insulin in euthyroid obese men

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.

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.

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.

In obese males, insulin resistance is significantly related with impairment of thyroid function, and this situation seems to be attenuated with age.