Dynamic changes in frailty status and the risk of incident low back pain: a nationwide cohort study based on the China health and retirement longitudinal study

BACKGROUND: Low back pain (LBP) is a leading cause of global disability. While frailty is a known risk factor, previous studies have been largely cross-sectional, thus the impact of dynamic changes in frailty on incident LBP is unclear. This study aimed to investigate the association of changes in frailty status with incident LBP. METHODS: This prospective cohort study utilized data from the China Health and Retirement Longitudinal Study (CHARLS), including 9,174 participants aged ≥45 years without LBP at the start of follow-up. Frailty status (robust, pre-frail, frail) was determined using a 30-item Frailty Index (FI) at baseline (2011) and two years later (2013). Dynamic changes were defined by transitions between these states. Incident LBP was the primary outcome, ascertained via follow-up until 2020. Multivariable Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS: The study included 9,174 participants (mean age 59.2 years; 47.9% female) followed for a median of 7.48 years, during which 3,437 incident LBP cases were identified. Compared with participants who remained robust, those who progressed to a pre-frail or frail status had a significantly increased risk of incident LBP (HR 1.48, 95% CI 1.32-1.66). Progression from pre-frail to frail also increased risk (HR 1.51, 95% CI 1.35-1.69) compared to remaining pre-frail. Conversely, recovery was protective; participants improving from pre-frail to robust (HR 0.69, 95% CI 0.61-0.78) or from frail to less frail status (HR 0.77, 95% CI 0.66-0.90) had significantly lower risks than their stable counterparts. CONCLUSIONS: Frailty is a dynamic and powerful predictor of incident LBP. Progression towards frailty significantly elevates LBP risk, while recovery is protective. These findings establish a temporal relationship, positioning frailty as a critical, modifiable target for LBP prevention. Integrating frailty assessment into routine clinical care may be a key strategy to reduce the burden of LBP in aging populations.