Bidirectional association between asthma and cardiovascular disease in middle-aged and older Chinese adults: the mediating effect of frailty

The bidirectional relationship between asthma and cardiovascular disease (CVD) among aging populations remains insufficiently explored, especially regarding potential mediating mechanisms. The objective of this study is to explore the bidirectional effects between asthma and CVD, with focus on frailty as a potential mediator. We utilized longitudinal data (2011–2018) from the China Health and Retirement Longitudinal Study (CHARLS) to analyze two cohorts: 7,910 CVD-free participants and 8,897 asthma-free participants. Frailty was evaluated based on a 29-component frailty index (FI). Bidirectional associations were examined using Cox proportional hazards regression models, with progressive adjustments for sociodemographic, lifestyle, and clinical variables. Mediation analysis assessed the mediating role of FI, utilizing bootstrap methods. baseline asthma correlated with a 74.6% heightened risk of new-onset CVD (HR = 1.746, 95% CI: 1.351–2.256) after full adjustment, whereas baseline CVD correlated with a 62.1% heightened risk of developing incident asthma (HR = 1.621, 95% CI: 1.207–2.176). Bidirectional associations were examined using Cox regression models. FI accounted for 15.57% of the relationship between CVD and asthma, as indicated by the mediation analysis (indirect effect = 0.005, 95% CI: 0.002–0.007), but did not mediate the opposite pathway. Subgroup analyses revealed consistent effects across demographic and clinical subgroups (all interaction p > 0.05). This research offers new insights into bidirectional associations between asthma and CVD in older Chinese adults, with partial mediation by frailty in the CVD→ asthma pathway. Findings highlight the need for integrated management and suggest frailty may serve as a target for intervention.