Association between body mass index and disability among older population in China: analysis of 2011-2020 data from the China Health and Retirement Longitudinal Study

BACKGROUND: The study explored the relationship between body mass index (BMI) and activities of daily living (ADL) disability among Chinese older adults. METHODS: Using 2011-2020 data from the China Health and Retirement Longitudinal Study, we included 3975 older individuals and assessed their baseline BMI, ADL disability, other covariates, and ADL disability over the follow-up period. Cox proportional hazards regression, restricted cubic spline, and two-piecewise linear regression models were performed. We also conducted subgroup analyses to explore effect heterogeneity across different subpopulations and sensitivity analyses to confirm the robustness of our findings. RESULTS: During a median follow-up of seven years, 2003 participants developed ADL disability. The Cox proportional hazards models demonstrated a significant association between BMI and the risk of ADL disability. When BMI was categorised into groups, only obese older adults exhibited a significantly higher risk of ADL disability compared to those with normal weight. The restricted cubic spline model further revealed a nonlinear U-shaped relationship between continuous BMI and ADL disability risk, indicating that the risk of ADL disability initially decreased and then increased with rising BMI. Subgroup analyses revealed that the U-shaped relationship was observed only among individuals aged 60-69 years and female older adults, while sensitivity analyses consistently confirmed the robustness of this U-shaped association between BMI and ADL disability risk. CONCLUSIONS: A nonlinear U-shaped relationship between BMI and ADL disability risk was observed among Chinese adults aged 60-69 and older female adults, suggesting that both high and low BMI are associated with increased ADL disability risk. Despite limitations such as baseline-only BMI measurements, observational study design, potential residual confounding, and limited generalisability beyond Chinese older adults, these findings highlight the importance of routine BMI screening and targeted weight management strategies to help prevent or delay the onset of ADL disability in older adults.