Association of socioeconomic status with premature cardiovascular mortality and its metabolic mediators: evidence from a nationwide cohort study

Background Lower individual socioeconomic status (SES) is associated with an elevated risk of mortality. However, studies exploring its association with premature cardiovascular disease (CVD) mortality and the potential mediating mechanisms remain limited. Purpose To explore the association between individual SES and premature CVD mortality, examine its variations across different populations, and analyze the role of individual factors as potential mediators, as well as the population attributable fractions (PAF) for the identified mediation pathways. Methods Based on the ChinaHEART (Health Evaluation And risk Reduction through nationwide Teamwork), a nationwide, population-based cohort study, we collected 1,702,767 participants aged 35-75 years, selected as a representative sample of the entire cohort between November 2014 and December 2023, based on project ID numbers ending in 1, 3, 5, or 7. Mortality records were through a linkage of data with the National Mortality Surveillance System and Vital Registration. Individual comprehensive SES was constructed through latent class analysis by integrating education, occupation, and household income. The Cox proportional hazards model was used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs), assessing the association between SES and the risk of premature cardiovascular disease mortality, as well as its variations across different populations. Furthermore, we explored the potential mediating role of various individual factors and calculated pathway-specific population attributable fractions （ps-PAFs）for the identified mediators. Results Among the 1,702,767 included participants with an average age of 56·2±10.0 years, 59·0% were female. During the follow-up with a median of 5·0 years, 15,272 premature CVD mortality cases were confirmed. Compared to individuals with high individual SES, those with low SES exhibited significantly associated with an increased risk of premature CVD mortality (HR=2.04, 95% CI: 1.89-2.20). A stronger association was observed among individuals aged over 60 years. The association between individual SES and premature CVD mortality was mediated by history of hypertension, obesity, and unhealthy lifestyle factors, with less physical activity demonstrating the strongest mediating effect. Among these mediating pathways, smoking accounted for the largest PAF. Conclusion The findings indicate that lower individual SES is significantly associated with an increased risk of premature CVD mortality, with a history of hypertension, obesity, and unhealthy lifestyle behaviors serving as mediators.