Association of depressive symptoms with ambient PM_2.5 in middle-aged and elderly Chinese adults: A cross-sectional study from the China health and Retirement Longitudinal Study wave 4

Depressive symptoms have become a serious public health issue worldwide. Several studies showed that air pollution, especially fine particulate matter (PM_2.5), may be a risk factor of mental disorders. However, existing studies reported inconsistent results and little evidence is available in developing countries, like China. To fill the gap, in this study, we explored the relationship between ambient PM_2.5 exposure and depressive symptoms among middle-aged and elderly Chinese adults in the Chinese Health and Retirement Longitudinal Study (CHARLS). The social and demographic variables and depressive symptoms were obtained from the Wave4 of CHARLS in 2018. PM_2.5 concentrations were obtained from the national urban air quality real-time release platform of China Environmental Monitoring Station. We applied generalized linear mixed models to determine the association between PM_2.5 exposure and depressive symptoms. A total of 15,105 middle-aged and elderly adults from CHARLS Wave4 were included in the analyses. We found positive impact of ambient PM_2.5 on depressive symptoms for the exposure windows of 30-day, 60-day, 120-day, 180-day, 1-year and 2-year. The most significant increase was observed for 180-day moving average. For every 10 μg/m³ increment in PM_2.5 exposure, the incidence of depressive symptoms increased by 9% (OR = 1.09; 95%CI: 1.05, 1.14) after adjusting for age, sex and residence. In interaction analyses, we found PM_2.5 had weaker effect on depressive symptoms among people who used to drink alcohol (OR = 1.05; 95%CI: 1.00, 1.10) and exercise (OR = 1.10; 95%CI: 1.02, 1.18). People living in western China (OR = 1.09; 95%CI: 1.03, 1.16) were more vulnerable than those living in eastern China (OR = 0.99; 95%CI: 0.94, 1.05). In conclusion, exposure to PM_2.5 was significantly associated with depressive symptoms in middle-aged and elder Chinese adults, particularly for people who never drink, with lower physical activity levels, or lived in western China.