Higher Prevalence of Thyroid Dysfunction in Type 2 Diabetes Mellitus: Effects on Glycemic Control, Diabetic Complications and Comorbidities

<i>Background and Objectives</i>: Thyroid dysfunction (TD) is more frequently observed in patients with diabetes mellitus (DM) compared to the general population. This study aims to determine the prevalence of TD in a large cohort of patients diagnosed with type 2 diabetes mellitus (T2DM) and to evaluate its possible impact on glycemic control, comorbidities, and diabetes-related complications. <i>Materials and Methods</i>: A total of 723 patients with type 2 diabetes mellitus (47.9% female, 52.1% male) were retrospectively evaluated. Demographic information of the patients, comprehensive history including onset and duration of DM and also comorbid diseases, diabetes-related complications, laboratory results, antidiabetic drugs and presence of TD were recorded and analyzed. <i>Results</i>: The prevalence of TD was 21.4% in 723 patients. Dyslipidemia was the most common comorbidity (63.6%). Patients with TD had significantly higher baseline BMI and longer diabetes duration (<i>p</i> = 0.007 and <i>p</i> = 0.048, respectively). Overall complication and comorbidity rates were 80.1% and 66%. TD was more common in females (73.4% vs. 26.6%; <i>p</i> < 0.001). Hypertension (69.5% vs. 58.7%) and neuropathy (40.9% vs. 33.0%) were significantly more frequent in the TD group (<i>p</i> < 0.05 for both). The total comorbidity rate was also higher in TD-positive patients (72.7% vs. 64.1%; <i>p</i> = 0.046). A significant positive correlation was observed between BMI and TSH levels. <i>Conclusions</i>: The increased prevalence of TD in patients with T2DM was clearly demonstrated. Female gender was identified as an independent risk factor, while elevated BMI and longer diabetes duration showed significant associations with TD status. The coexistence of TD and T2DM may contribute to a higher risk of diabetic complications and comorbidities. Routine screening of thyroid function is recommended to enable early identification and improve the overall clinical management.