Changes in Thyroid Hormones and Free Triiodothyronine-to-Free Thyroxine Ratio in Euthyroid Patients with Obesity in Terms of Different Glucose Metabolism Statuses

Abstract

Objective: The variations of thyroid hormones within normal ranges are observed in different metabolic conditions. Considering available data, levels of thyroid hormones change in obesity and type 2 diabetes mellitus (DM) in opposite ways. This study aimed to evaluate thyroid hormone levels and free triiodothyronine-to-free thyroxine (fT3/fT4) ratios in different glucose metabolism statuses of euthyroid patients with obesity. Material and Methods: This retrospective study evaluated thyroid hormones and the fT3/fT4 ratio of 209 patients with obesity who were grouped according to their glucose metabolism statuses. Results: One hundred and thirty-one (62.7%) patients had normal glucose tolerance, 41 (19.6%) patients had prediabetes, and 37 (17.7%) patients had DM. Serum fT4 level was found to be higher in patients with DM compared to patients with normal glucose tolerance (p=0.009), although no difference was observed in serum thyroid-stimulating hormone and fT3 levels among groups. FT3/fT4 ratio was determined to be lower in patients with DM than patients with normal glucose tolerance (p=0.012). Hemoglobin A1c was independently and positively associated with fT4 (β=0.345, r 2 =0.119, p=0.003) and negatively associated with fT3/fT4 ratio (β=-0.371, r 2 =0.138, p=0.001). Conclusion: Serum fT4 level increased, and fT3/fT4 ratio decreased in patients with type 2 DM independent of the degree of obesity. The interaction of DM with thyroid hormones in our cohort seemed to overcome obesityrelated changes in thyroid functions.