Obesity is Associated with Increased Thyroid Volume and Heterogeneity in Ultrasonography

Objective: The aim of the present study was to investigate the possible association between obesity and thyroid functions and thyroid morphology. Material and Methods: A total of 674 subjects-121 obese and 553 nonobese-were included in the study. Body mass index, serum thyrotrophic, free triiodothyronine (fT3), free thyroxine (fT4), antithyroid peroxidase antibody, and antithyroglobulin antibody (antiTg) were evaluated in each subject. The subjects with thyroid nodules in ultrasonography (USG) were excluded. The thyroid volume of each subject was calculated and analyzed. Results: Obesity was significantly associated with increased age and low fT4 in univariate analysis (p<0.05). With multivariate analysis, the odds of obesity was found to increase by 21.8% (95% CI: 12.4-31.9%) for each 5-year increase in age anddecrease by 53.1% (95% CI: 0.4-77.9%) for each 1 ng/dL increase in fT4. The odds of obesity in patients with positive antiTg was 1.603 (95% 1.047-2.454) times higher than the odds of obesity in patients with negative antiTg. The median total thyroid volume was significantly higher in obese as compared to nonobese subjects (12.11 mL vs. 10.77 mL, p<0.001). Heterogeneous gland with negative thyroid antibodies was observed in 17 (14%) obese and 40 (7.2%) nonobese subjects (p=0.024). Conclusion: Obesity was positively associated with antiTg and age, whereas negatively associated with fT4. Approximately, in every seven obese subjects, one showed heterogeneity in US despite negative thyroid autoantibodies. This suggests that the value of US in the diagnosis of autoimmune thyroiditis might decrease in obese patients.