Associations of area-level socioeconomic status and individual factors with mortality in China: a nationwide prospective cohort study

Background Although socioeconomic inequality in mortality has long been a public health focus, the associations of area-level socioeconomic status (SES) and individual-level factors with mortality have not been well investigated, especially in China with rapid industrial development. Methods In this nationwide, population-based, prospective cohort study, adults aged over 40 from 29 counties were included in the China Cardiometabolic Disease and Cancer Cohort study. The composite area deprivation index of area-level SES was generated from national census data and categorised into tertiles. Cox proportional hazards models were fitted to calculate HRs and 95% CIs for area-level SES with the risk of mortality, and comprehensive individual socioeconomic, lifestyle, and metabolic factors were examined as potential mediators. Results A total of 174 004 participants were included. During a median follow-up of 10.1 years, low area-level SES was associated with 34% increased risk of all-cause mortality (95% CI 1.27 to 1.42), 76% increased risk of cardiovascular disease (CVD) mortality (95% CI 1.59 to 1.94) and 13% increased risk of non-CVD mortality (95% CI 1.05 to 1.21) compared with high area-level SES. The association between area-level SES and all-cause mortality was partly mediated by individual socioeconomic, lifestyle and metabolic factors, contributing 3.8%, 20.7% and 8.9%, respectively. Furthermore, individuals with low area-level SES and low individual SES, unhealthy lifestyles, or poor metabolic status had the highest risk of mortality. Conclusions Significant area-level socioeconomic inequalities in mortality exist in China. Comprehensive interventions targeting both area-level circumstances and individual socioeconomic, lifestyle and metabolic factors were key strategies to reduce these inequalities.