Changing clinical characteristics according to insulin resistance and insulin secretion in newly diagnosed type 2 diabetic patients in Korea

Background: The role of increased insulin resistance in the pathogenesis of type 2 diabetes has been emphasized in Asian populations. Thus, we evaluated the proportion of insulin resistance and the insulin secretory capacity in patients with early phase type 2 diabetes in Korea. Methods: We performed a cross-sectional analysis of 1,314 drug-naive patients with newly diagnosed diabetes from primary care clinics nationwide. The homeostasis model assessment of insulin resistance (HOMA-IR) was used as an index to measure insulin resistance, which was defined as a HOMA-IR ≥2.5. Insulin secretory defects were classified based on fasting plasma C-peptide levels: severe (<1.1 ng/mL), moderate (1.1 to 1.7 ng/mL) and mild to non-insulin secretory defect (≥1.7 ng/mL). Results: The mean body mass index (BMI) was 25.2 kg/m²; 77% of patients had BMIs > 23.0 kg/m². Up to 50% of patients had central obesity based on their waist circumference (≥90 cm in men and 85 cm in women), and 70.6% had metabolic syndrome. Overall, 59.5% of subjects had insulin resistance, and 20.2% demonstrated a moderate to severe insulin secretory defect. Among those with insulin resistance, a high proportion of subjects (79.0%) had a mild or no insulin secretory defect. Only 2.6% of the men and 1.9% of the women had both insulin resistance and a moderate to severe insulin secretory defect. Conclusion: In this study, patients with early phase type 2 diabetes demonstrated increased insulin resistance, but preserved insulin secretion, with a high prevalence of obesity and metabolic syndrome.