Combined Impact of Abdominal Obesity and Nontraditional Insulin Resistance Indices on Stroke Risk: Evidence from a Nationwide Prospective Cohort Study

Background: Stroke remains a leading cause of death and disability worldwide, with abdominal obesity (AO) and insulin resistance (IR) recognized as modifiable risk factors. However, their joint effects and potential mediating relationships with stroke risk remain unclear. Methods: This study enrolled 5,537 eligible middle-aged and older Chinese adults from the China Health and Retirement Longitudinal Study (CHARLS). AO was defined on the basis of waist circumference, and cumulative average nontraditional IR parameters were calculated from blood samples collected in 2011 and 2015. Cox proportional hazards models were used to assess adjusted associations, whereas Kaplan-Meier analysis was used to estimate cumulative hazards. Restricted cubic splines evaluated nonlinear relationships between nontraditional IR parameters and stroke risk among AO participants. Subgroup analyses stratified by age, gender, BMI, smoking, drinking, and hypertension were used to assess the interaction effects. Sensitivity analyses were used to examine the robustness of the results. Exploratory mediation analyses were performed, with emphasis on indices not directly incorporating waist circumference to reduce potential mathematical overlap with AO. Results: During a median follow-up of 57.2 months, 490 (8.85%) participants experienced stroke. Participants with both AO and elevated IR indices presented the highest stroke risk (P-trend <0.05). Among AO individuals, CVAI showed the highest AUC for stroke among the nontraditional IR indices (0.591, 95% CI, 0.560–0.622), indicating modest discriminative ability. Nonlinear associations between LAP, TyG-WC, and stroke risk were observed in non-AO individuals, with significant risk increases above thresholds (LAP 0.64; TyG-WC 594.09). Exploratory mediation analyses suggested potential bidirectional pathways, particularly for indices not directly incorporating waist circumference. Conclusion: AO and nontraditional IR parameters jointly contribute to stroke risk. The incorporation of these indices into clinical assessments may increase the accuracy of early stroke prevention strategies and improve risk stratification in middle-aged and older populations.