PM2.5 exposure modifies the association of physical activity with depressive symptoms and glaucoma in middle aged and elderly Chinese

It remains unclear that trade-off between the benefits of regular physical activity (PA) and the potentially harmful effects of exposure to PM_2.5 (particulate matter with aerodynamic diameter < 2.5 μm) in highly polluted regions. Therefore, we aimed to investigate the modification of PM_2.5 on the associations of PA volume and intensity with depressive symptoms and glaucoma in individuals with or without depressive symptoms. Data of this study was obtained from the China Health and Retirement Longitudinal Survey (CHARLS) implemented during 2011 to 2020. PA volume and intensity were measured by a standardized questionnaire; a machine learning prediction model was applied to ascertain the PM_2.5 concentrations. Cox proportional hazards regression models were employed to explore associations. A total of 20,930 participants were finally included, with 11,214 analyzed for PA and depressive symptom risk and 16,965 analyzed for PA and glaucoma risk. PA volume or intensity was independent protective factor for incident depressive symptoms, while PM_2.5 was independent risk factor for depressive symptoms and glaucoma in participants with or without depressive symptoms. Among participants with low PM_2.5 exposure (< 35 micrograms per cubic meter [µg/m³]), PA volume or intensity showed an inverse association with the risk of incident depressive symptoms, but insignificant associations between PA volume or intensity and glaucoma risk were observed in either participants with or without depressive symptoms. Among participants with high PM_2.5 exposure (≥ 35 µg/m³), higher PA volume or intensity increased the risks of depressive symptoms and glaucoma. Higher PA level was associated with a reduced risk of depressive symptoms only among participants with low PM_2.5 exposure, and higher PA did not decrease the risk of glaucoma regardless of PM_2.5 level. Our findings recommend regular PA to prevent depressive symptoms in less polluted regions and reinforce the importance of air quality improvement.