Joint assessment of frailty index and metabolic syndrome score for cardiovascular disease in middle aged and older Chinese adults: insights from a national cohort study 2011–2020

BACKGROUND: Both frailty and metabolic syndrome (Met) frequently coexist in older adults, creating a complex syndemic that possibly amplifies cardiovascular disease (CVD) risks. This study aims to evaluate whether frailty and metabolic syndrome severity have a synergistic impact on the risk of cardiovascular events among middle-aged and older cohorts in China. METHOD: We analyzed data from China Health and Retirement Longitudinal Study (CHARLS) 2011-2020 of 8,992 individuals. The associations of frailty (as represented by frailty index) and metabolic syndrome severity (as represented by metabolic syndrome score) with CVD risks were examined using Cox regression and restricted cubic splines. The predictive performance was assessed by receiver operating characteristic (ROC) curve analysis. Furthermore, potential mediating factors were investigated through mediation analysis. RESULT: Individuals with high frailty index (FI) and high metabolic syndrome score (MetS) (FI > 4.36 and MetS > 0.17) were at the highest CVD risk (HR = 1.295, 95% CI: 1.141-1.469), suggesting a synergistic association. High FI significantly mediated 10.8% of the association between the Met and CVD risk. Next, we established FI-MetS by multiplying the two indicators, which was independently associated with an increased risk of CVD (HR = 1.011 per 1-point increment, 95% CI 1.006-1.015). It showed a positive linear relationship with CVD risk. The predictive value of FI-MetS was greater than FI alone and MetS alone. CONCLUSION: Given its significant predictive capability regarding cardiovascular disease development in older Chinese cohorts, FI-MetS should be adopted as a primary tool for risk screening, superseding the use of separate frailty or metabolic syndrome assessments.