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.