Lifestyle Mediated the Relations of Socioeconomic Status with Risk of Frailty in Middle-Aged and Older Adults: Evidence from Three Prospective Cohorts

BACKGROUND: Socioeconomic status (SES) is a key social determinant of diverse health outcomes. This study examined the association of SES with the risk of frailty among adults aged over 45, and further explored the specific role of lifestyle. METHODS: A total of 26,978 individuals from three nationwide cohorts were included in the analysis, with 57.57% of them aged 60 years and older. Frailty was evaluated using the frailty index (FI) constructed from 40 health-related items, and frailty trajectories were identified using group-based trajectory modeling. Latent class analysis was conducted to determine the optimal SES pattern based on occupation, education, and income. The lifestyle score comprised smoking, drinking, exercise, sleep, social participation, and body shape. Cox and Logistic regression models, mediation and joint analysis, and multiple sensitivity analysis were used. RESULTS: Over a median follow-up of 7.49 years, 7,636 participants developed frailty. Low SES was a risk factor for frailty (HR = 1.51, 95% CI: 1.43-1.60) and high-ascending frailty trajectory (OR = 1.73, 95% CI: 1.60-1.87). Lifestyle mediated 8.82% of the association for SES and frailty, 8.37% of the association for SES and high-ascending frailty trajectory. Participants exhibiting both low SES and unhealthy lifestyle demonstrated the highest risk of frailty (HR = 2.13, 95% CI: 1.94-2.34) and high-ascending frailty trajectory (OR = 2.55, 95% CI: 2.23-2.92). CONCLUSIONS: Unhealthy lifestyle partially mediated the association of low SES with frailty in adults aged over 45. Therefore, simultaneous interventions tailored to socioeconomic and lifestyle factors are needed to prevent frailty.