Comparative Evaluation of Thyroid Function in Patients with Type 2 Diabetes Mellitus and Non-diabetic Individuals

Abstract

Background: Type 2 diabetes mellitus (T2DM) is a major metabolic disorder frequently associated with abnormalities in other endocrine systems, particularly the thyroid gland. Thyroid dysfunction may adversely affect glycemic control, lipid metabolism, and cardiovascular risk, yet comparative data between diabetic and non-diabetic individuals remain limited in many populations. Objective: To evaluate and compare thyroid function parameters and the prevalence of thyroid dysfunction between patients with type 2 diabetes mellitus and non-diabetic individuals, and to assess their association with glycemic control and sex. Methods: This cross-sectional study was conducted at a tertiary care hospital between June and August 2024. A total of 200 adults were enrolled, including 100 patients with T2DM and 100 non-diabetic controls. Fasting blood glucose, 2-hour postprandial glucose, HbA1c, lipid profile, serum creatinine, thyroid-stimulating hormone (TSH), and free thyroxine (FT4) were measured. Thyroid dysfunction was categorized as subclinical or overt hypothyroidism. Statistical analyses included independent t-tests, chi-square tests, and Pearson correlation analysis. Results: Patients with T2DM had significantly higher fasting glucose (156.4 ± 38.2 vs 92.6 ± 10.4 mg/dL), HbA1c (8.4 ± 1.2% vs 5.4 ± 0.4%), and adverse lipid profiles compared to controls (all p < 0.001). Thyroid dysfunction was significantly more prevalent in the T2DM group than in non-diabetic individuals (32.0% vs 14.0%, p = 0.003), with subclinical hypothyroidism being the most common abnormality (22.0%). Mean TSH levels were higher in patients with T2DM (4.2 ± 1.6 vs 2.6 ± 1.1 mIU/L; p < 0.001), while FT4 levels were lower (p = 0.01). Female patients with T2DM showed a higher prevalence of thyroid dysfunction compared to males (42.9% vs 24.1%, p = 0.04). TSH demonstrated a significant positive correlation with HbA1c (r = 0.46, p < 0.001), while FT4 showed a negative correlation (r = −0.29, p = 0.004); no such associations were observed in non-diabetic individuals. Conclusion: Thyroid dysfunction, particularly subclinical hypothyroidism, is significantly more prevalent among patients with type 2 diabetes mellitus and is associated with poorer glycemic control, with a higher burden observed in female patients.