Exercise is associated with lower all-cause mortality among older adults: a national cohort survival analysis with county-level industrial air pollution indicators.

BACKGROUND: Accelerated global population aging has increased the urgency of identifying effective non-pharmacological strategies to reduce mortality risk among older adults. Although exercise serves as a key protective factor, industrial air pollution may attenuate its health benefits, and this interaction remains unclear. This study aims to investigate whether county-level industrial air pollution indicators modify the association between exercise and all-cause mortality among older adults. METHODS: A longitudinal survival analysis was performed using the Chinese Longitudinal Healthy Longevity Survey (2008-2014) with multistage stratified sampling across 23 provinces. The analysis included 16,954 participants aged ≥ 65 years with three follow-up waves spanning 6 years. Self-reported current exercise habits, survival outcomes, health status, sex, smoking status, baseline age, residence, body mass index, functional status, and comorbidity count were extracted. County-level industrial air pollution indicators (annual soot and SO2 emissions, and removals) were matched to individuals according to their residence. All pollution indicators were standardized, and time-varying covariates were updated at each wave. Cox proportional hazards models were constructed sequentially: univariate models for core variables (exercise habits and industrial air pollution indicators), two-way interaction models, and multivariate models with sequential adjustment for covariates (sex, health status, baseline age, smoking status, residence, BMI, functional status, and comorbidity count). RESULTS: Self-reported current exercise habits were significantly associated with lower all-cause mortality risk after multivariate adjustment (fully adjusted HR = 0.835, 95% CI: 0.773-0.902, p < 0.001). SO2 emissions showed a weak association with survival risk in univariate analysis (HR = 1.023, 95% CI: 0.942-1.111, p = 0.585). The association estimate was further attenuated after multivariate adjustment (fully adjusted HR = 1.001, 95% CI: 0.874-1.146, p = 0.992). Soot-related indicators showed no significant mortality associations. The interaction between exercise habits and each of the four industrial air pollution indicators was not significant (all p > 0.05). CONCLUSION: Self-reported current exercise habits were consistently associated with lower all-cause mortality among Chinese older adults, and this association was robust to adjustment for covariates. No statistically significant multiplicative interaction was detected between exercise habits and any of the four pollution indicators. Continued attention to industrial emission control remains warranted, while promoting habitual exercise among older adults may be beneficial in areas with industrial emissions.