Alterations of Thyroid Functions in Obesity: Is There any Impact of Co-Existence of Type 2 Diabetes Mellitus?

Aim: Little is known about the effect of coexistent type 2 diabetes mellitus (DM) on thyroid functions in obesity. We aimed to evaluate the thyroid function in the both diabetic and nondiabetic obese patients. Materials and Methods: 145 obese patients admitted to our department, between June 2014 and May 2016, were included in the study. The patients with known thyroid dysfunction were excluded from the study. The patients were grouped according to their BMI (body mass index), co-existence of type 2 DM, and TSH (thyroid stimulating hormone). Data were collected retrospectively and analyzed. Results: No difference was observed between diabetic and nondiabetic groups for the mean age, body weight, fT3 (free T3), fT4 (free T4), BMI, TSH. Primary hypothyroidism, subclinical hypothyroidism and hyperthyroidism were determined in 1.4, 0.7 and 2.8 % of the patients, respectively; no difference was found between diabetic and nondiabetic groups (p=0.588). There was no significant correlation between BMI and TSH (r=0.030, p=0.717).Distribution of patients in different TSH groups between diabetic and nondiabetic groups were similar (p=0.533). There were positive correlations between BMI and, fT4 or fT3 (r=0.274, p=0.001; r=0.280, p=0.002; respectively). Although 1.4% of all patients had isolated elevation of fT4, there was no difference between groups (p=0.178). 24.6% of diabetic, 28.4% of nondiabetic and 26.6% of all patients had isolated elevation of fT3; however, no difference was found (p=0.634). Conclusions: Our study suggested that obesity could be associated with elevated fT4 and fT3. Elevation of fT3 and fT4 with increasing BMI may be as response to increased metabolic rate. We found no difference between diabetic and nondiabetic groups concerning to fT4 and fT3 elevation. As a result, co–existence of type 2 DM seems to have no effect on thyroid functions