Obesity without comorbidity may also lead to non-thyroidal illness syndrome.

Background: Obesity mediates a series of operations in the body by increasing the production of proinflammatory cytokines. Cytokines play an important role in the development of non-thyroidal illness syndrome (NTIS).

Objectives: The aim of this study was to investigate the association between obesity and NTIS.

Material And Methods: A total of 423 subjects were included. The study group was comprised of 219 obese patients without any comorbid disease and the control group was comprised of 204 healthy subjects. Body mass index (BMI), thyroid hormone levels, high-sensitivity C-reactive protein (hs-CRP) levels, erythrocyte sedimentation rate (ESR), complete blood count, and other biochemical parameters were measured. Frequencies of NTIS were calculated. MedCalc 12.5 software program (MedCalc, Ostend, Belgium) was used for statistical analysis.

Results: Groups were statistically different according to BMI (p < 0.001). The mean BMIs of the study and the control group were 34.6 ±5.0 kg/m2 and 22.6 ±1.8 kg/m2, respectively. Obese patients had higher serum hs-CRP levels, ESR and white blood cells (WBC) levels (0.99 ±3.17 mg/L vs 0.39 ±1.09 mg/L; 17.2 ±10.6 mm/h vs 12.6 ±8.0 mm/h; 7.8 ±2.1 103/μL vs 6.9 ±1.5 103/μL, respectively; p < 0.001). There were 21 (9.5%) obese patients with NTIS, while there were none NTIS cases in the control group. The difference was statistically significant (p < 0.001). There was a strong association between obesity and NTIS (odds ratio (OR) = 44.2, confidence interval (CI) = 95% 2.66-736.3; p = 0.0082).

Conclusions: Inflammation, which is strongly associated with adipose tissue, may lead to NTIS in obese patients without any comorbid disease.