The Association Between the Frailty Index and Arthritis Among Middle-Aged and Older Chinese Adults (≥45 Years): Evidence From the GBD 2023, CHARLS, and Mendelian Randomization Analyses

Abstract Background Arthritis is a common musculoskeletal disorder affecting more than 600 million people worldwide. It substantially impairs quality of life and mental health and increases reliance on opioid medications. Despite its high prevalence, effective prevention and management remain limited. Growing evidence suggests an association between frailty—reflecting reduced physiological reserve—and the risk of arthritis. This study aimed to quantify the burden of arthritis among Chinese adults aged ≥ 45 years and to examine the causal relationship between frailty and arthritis risk. Methods We used data from the Global Burden of Disease (GBD) 2023 to estimate incidence, prevalence, and disability-adjusted life years (DALYs) of arthritis among Chinese adults aged ≥ 45 years, including temporal trends (1990–2023), spatial patterns, and age-standardized rates, with subgroup analyses by sex and age. Associations between frailty and arthritis were assessed using China Health and Retirement Longitudinal Study (CHARLS) data with multivariable logistic regression and progressive adjustment for demographic, socioeconomic, and health-related confounders. Subgroup and sensitivity analyses were conducted to evaluate robustness. Two-sample Mendelian randomization (MR) using genetic instruments for frailty was performed to investigate potential causal effects on overall arthritis and osteoarthritis. Results From 1990 to 2023, age-standardized rates of arthritis among Chinese adults aged ≥ 45 years remained relatively stable, whereas the absolute burden increased substantially. In 2023, an estimated 154.8 million individuals (95% uncertainty interval: 133.9–177.6 million) were affected, accounting for nearly one-third of the global burden in this age group. The burden was higher in women and older adults. Higher frailty was strongly associated with increased arthritis risk. Compared with the lowest frailty quartile, individuals in the highest quartile had a more than twofold increased risk (odds ratio = 2.68, 95% confidence interval: 1.65–4.35; p < 0.001) after full adjustment. MR analyses provided additional evidence consistent with a potential causal effect of frailty on arthritis. Conclusions Arthritis remains a major and growing public health challenge among middle-aged and older Chinese adults. Frailty shows strong predictive value for arthritis risk and may serve as an effective tool for risk stratification. Integrating frailty assessment into clinical practice and public health strategies may enable earlier prevention and improved management.