Metabolic Syndrome Severity and All-Cause Mortality in a Nationally Representative Cohort 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 effect modification 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 10.8% lower mortality risk (HR = 0.892, 95% CI: 0.817–0.973). The protective effect was concentrated in Q4 vs. Q1 (HR = 0.840, 95% CI: 0.713–0.989). Subgroup analyses showed stronger associations in those ≥ 80 years (HR = 0.861, 95% CI: 0.783–0.945) and urban residents (HR = 0.466, 95% CI: 0.293–0.741). Restricted cubic splines confirmed a linear inverse association overall and among the ≥ 80 years group. Conclusions 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 elderly, warranting further mechanistic studies.