Physical activity modifies the association between ambient air pollution and comorbid depression and disability in activities of daily living

This study aims to explore the effects of physical activity, ambient air pollutants, and their interactions on the risk of depression, ADL disability, and their comorbidity. The study followed 11,875 adults aged 45 and older from China. Time-varying Cox proportional hazards regression models, adjusted for year, month, season, and spatial autocorrelation, city, demographic, health-related behavioral, and socioeconomic factors, were used to analyze the relationships between pollutants and various health outcomes. Over a median follow-up of 7 years, 2,227 participants developed depression (18.8%), 212 developed ADL disability (1.8%), and 183 developed comorbidity (1.5%). Throughout the follow-up period, the annual average concentration of PM₁, PM_2.5, PM₁₀, O₃ and NO₂, had a median value of 25.2 (IQR 18.2, 33.0) µg/m³, 43.9 (IQR 31.6, 58.8) µg/m³, 76.2 (IQR 53.3, 103.0) µg/m³, 88.6 (IQR 82.0, 97.9) µg/m³, and 26.0 (IQR 19.4, 33.5) µg/m³, respectively. For every 10 µg/m³ increase in pollutants, the risk of comorbid depression and ADL disability increased significantly: PM₁ by 33.3% (aHR = 1.33, 95% CI 1.24-1.43), PM_2.5 by 16% (aHR = 1.16, 95% CI 1.11-1.20), PM₁₀ by 7% (aHR = 1.07, 95% CI 1.05-1.10), O₃ by 14% (aHR = 1.14, 95% CI 1.08-1.20), and NO₂ by 44% (aHR = 1.44, 95% CI 1.33-1.55). Physically active individuals had significantly reduced risks of comorbidity compared with non-physically active ones by 10.2% for PM_2.5 and 6.1% for PM₁₀. Higher air pollution levels are associated with increased risks of depression and comorbid depression and ADL disability. However, physical activity may mitigate these risks for these two conditions.