Socioeconomic Inequality in Chronic Complications of Type 2 Diabetes Mellitus in Iran: Concentration Index and Decomposition Approach

Introduction: In Iran, evidence regarding the impact of socioeconomic status (SES) on the progression and complications of type 2 diabetes mellitus (T2DM) are sparse and needs growing body of research. Socioeconomic status is a complex construct and its impact on the health outcomes should be evaluated in an efficient and flexible way. The aim of this study is to investigate socioeconomic inequality in chronic complications among patients with T2DM using the concentration index and, also determine the contribution of various variables on inequality through the decomposition analysis. Methods: This cross-sectional study included patients with T2DM who received care at the diabetes clinic in Hamadan from April to September 2023. Demographic information, household assets, and diabetes-related factors were obtained from medical records and face-to-face interviews. In this study, a healthy lifestyle was evaluated based on four characteristics of healthy behavior (smoking, dietary pattern, weight control, and physical activity) and the score obtained for each individual. The asset Index was considered as a measure of SES based on household assets and was created using principal component analysis. To examine the relationship between diabetes complications and independent variables, univariate logistic regression models were employed, and the concentration index (CI) was used to assess inequality. The decomposition approach was utilized to determine the contribution of each factor to the inequality. Results: A total of 530 patients (60% females and 54.9% less than 60 years) were included. In the study population, 22.3%, 9.5%, and 4.7% had retinopathy, kidney failure, and diabetic foot ulcers, respectively. The CI for retinopathy, kidney failure, and foot ulcers were [(CI: -0.248, p<0.001), (CI: -0.085, p<0.001), (CI: -0.125, p<0.001), respectively]. Factors with the greatest contribution to socioeconomic inequality for retinopathy were economic status (57.25%), duration of T2DM (21.77%), and adherence to prescribed medication (10.89%), for kidney failure were economic status (38.83%), hypertension (24.71%), and education level (14.11%), and for foot ulcers were economic status (24%), duration of T2DM (24%), education level (20.80%), and HbA1c level (18.40%). Conclusion: This study demonstrated that socioeconomic inequality in chronic complications of T2DM with greatest contribution for economic status. It is recommended that policymakers and health professionals consider the main causes of socioeconomic inequality in the chronic complications of T2DM when developing health strategies.