Bidirectional adverse effects of low and high atmospheric humidity on arthritis in middle-aged and older adults: evidence from propensity score matching and comprehensive mosdeling approaches

BACKGROUND: Atmospheric humidity is a common environmental factor, and its abnormal fluctuations are associated with various diseases. This study investigated the relationship between atmospheric humidity and arthritis prevalence. METHODS: Data were obtained from the China Health and Retirement Longitudinal Study (CHARLS). Propensity Score Matching (PSM) and Inverse Probability of Treatment Weighting (IPTW) were used to control for confounders. Multivariate logistic regression and Restricted Cubic Spline (RCS) models were employed to assess linear and nonlinear associations. Stratified analysis and mixture models (WQS and BKMR) were applied to examine subgroup interactions and joint effects. RESULTS: Among 25,411 participants (9,218 arthritis cases), no linear association was found. RCS analysis revealed U-shaped relationships between three humidity indicators (RH, AVP, DPT) and arthritis (all P-nonlinear < 0.05). Both low (Q1) and high (Q3) humidity levels were significantly associated with higher odds of arthritis in fully adjusted models. A significant age interaction was observed only for AVP, with higher susceptibility in those under 65. Mixed-effects models indicated that combined humidity exposure was associated with higher odds of arthritis, with RH contributing most. CONCLUSION: This study clarifies the nonlinear impact and threshold effect of atmospheric humidity on arthritis, suggesting both low and high humidity may promote arthritis. Maintaining appropriate humidity levels could help reduce probability of disease.