"Comparison of thyroid volume, TSH, free t4 and the prevalence of thyroid nodules in obese and non-obese subjects and correlation of these parameters with insulin resistance status"

Background: To compare thyroid volume, thyroid stimulating hormone (TSH), free t4 and the prevalence of thyroid nodules between obese and non-obese subjects. Also, the association between BMI and insulin resistance status with various parameters of thyroid gland was evaluated.

Methods: Fifty-two patients with obesity and 38 volunteers aged 20-50 years with normal body mass index (BMI), were enrolled in this cross-sectional study. Patients with diabetes, history of thyroid disorders, and patients, who were taking medications that influence their blood glucose or insulin levels or modified thyroid function tests, were excluded. TSH, free t4, insulin and glucose and thyroid sonography were carried out and the results compared between two groups. P<0.05 was considered as significant.

Results: Thyroid volume was higher (p<0.001) and free t4 was lower (p<0.001) in patients with obesity but there was no difference in TSH between groups. Prevalence of thyroid nodules was 15.7% and 10.8% in obese and non-obese groups, respectively (p=0.51). Frequency of nodules was significantly higher in insulin resistant than non- insulin resistant subjects (22% vs.2%, p=0.01). BMI was associated with thyroid volume (r=0.44, p<0.001) and free t4 (r=-0.35, p=0.001). HOMA-IR (homeostatic model assessment for insulin resistance) had no correlation with thyroid volume (p=0.38), but associated with free t4 (r=-0.25, p=0.01).

Conclusion: Free T4 was lower and volume of thyroid was higher in obese subjects, but TSH and frequency of thyroid nodules had no significant difference between obese and non-obese counterparts. Insulin resistant individuals had more nodules but thyroid volume was mainly associated with BMI.

Keywords: Function tests; Insulin resistance; Nodule; Obesity; Thyroid volume.