Health inequities in the comorbid risk of pneumoconiosis and chronic obstructive pulmonary disease: a nationwide study of age-related risk heterogeneity

Background Pneumoconiosis patients are at heightened risk of developing chronic obstructive pulmonary disease (COPD). While age is a known risk factor, its impact across different populations is unclear. Methods We included 9,964 pneumoconiosis patients from 27 Chinese provinces. Factors were identified using multivariable logistic regression, and the non-linear age–COPD risk association was examined with restricted cubic spline (RCS) modelling. Stratified analysis and interaction tests assessed sociodemographic heterogeneity. Sensitivity analyses comprised RCS models with varying knots and propensity score matching. Results The prevalence of COPD among patients with pneumoconiosis was 24.1%. Each additional year of age was associated with a significant increase in COPD risk (adjusted odds ratio [aOR] = 1.03, 95% confidence interval [CI]: 1.03–1.04). RCS analysis revealed a significant nonlinear relationship, with risk increasing steeply beyond age 55 years (P for overall < 0.001; P for nonlinear = 0.017). we identified subgroups with distinct risk patterns. Rural residents and those without work‑related injury insurance (WRII) demonstrated an earlier inflection point (53 years) followed by a steep increase in risk. In contrast, urban residents and individuals with WRII exhibited a later inflection point (at 61 and 59 years, respectively) and a more gradual rise in risk. The inflection point differed by 8 years between urban and rural residents and by 6 years between individuals with and without WRII. Sensitivity analyses verified the robustness of these findings. Conclusion The nonlinear relationship between age and COPD risk in pneumoconiosis is significantly modified by sociodemographic factors.