Metabolic syndrome severity and all-cause mortality in the CLHLS biomarker subsample of older Chinese adults

Background: Metabolic syndrome (MetS) is a cluster of risk factors that increases cardiometabolic disease and mortality. A continuous MetS Score has been developed to quantify MetS severity, but its association with all-cause mortality in older Chinese adults remains unclear. Methods: We analyzed 2,443 participants from the Chinese Longitudinal Healthy Longevity Survey (CLHLS, 2008-2018 and 2011-2018). MetS Score was derived by confirmatory factor analysis using triglycerides, HDL-C, fasting glucose, systolic blood pressure, and BMI. Participants were categorized into quartiles (Q1-Q4). Cox proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for all-cause mortality. Subgroup analyses examined heterogeneity by age, sex, residence, and other covariates, and restricted cubic splines explored dose-response relationships. Results: During 10,356 person-years of follow-up, 1,412 deaths occurred (136.3/1,000 person-years). Each 1-unit increase in MetS Score was associated with a 13.9% lower mortality risk (HR = 0.861, 95% CI: 0.787-0.942). The protective effect was concentrated in Q4 vs. Q1 (HR = 0.792, 95% CI: 0.669-0.938). Subgroup analyses showed stronger associations in those aged ≥80 years (HR = 0.785, 95% CI: 0.660-0.935), women (HR = 0.758, 95% CI: 0.617-0.931) and rural residents (HR = 0.817, 95% CI: 0.618-0.980). Restricted cubic splines confirmed a linear inverse association overall and among the ≥80 years group. Conclusion: MetS Score, reflecting MetS severity, was inversely associated with all-cause mortality in older Chinese adults, particularly among those aged ≥80 years. These findings suggest that higher MetS Score may paradoxically confer survival benefits in the older adults, warranting further mechanistic studies.