Relationship of thyroid function with body mass index, leptin, insulin sensitivity and adiponectin in euthyroid obese women

Background: A possible relationship between thyroid hormones and adipose tissue metabolism in humans has been suggested. Aim of the study: We sought to evaluate thyroid function and its possible relationship with body mass index (BMI), leptin, adiponectin and insulin sensitivity in euthyroid obese women. Materials and methods: Eighty-seven uncomplicated obese women (mean age 34.7 ± 9 years, mean BMI 40.1 ± 7 kg/m²) were studied. Levels of TSH, free thyroxine (FT4), free triiodothyronine (FT3), plasma adiponectin and leptin were evaluated. Insulin sensitivity was assessed by euglycaemic hyperinsulinaemic clamp (M index), fasting insulin and HOMA-IR. Results: Uncomplicated obese women with BMI > 40 kg/m² showed higher serum TSH than obese subjects with BMI < 40 kg/m² (P < 0.01). TSH was correlated with BMI (r = 0.44, P = 0.01) leptin (r = 0.41, P = 0.01), leptin/BMI ratio (r = 0.33, P = 0.03), body surface area (r = 0.26, P = 0.05), HOMA-IR (r = 0.245, P = 0.05) and inversely with adiponectin (r = -0.25, P = 0.05) and M index (r = -0.223 P = 0.05). Conclusions: Our data show that, although thyroid function was normal in the studied obese population, TSH and BMI were positively related. TSH has been found to be correlated also with leptin adjusted for BMI. TSH could represent a marker of altered energy balance in severe, but uncomplicated obese women.