Association between Air Pollution and Depressive Symptoms: Effect modification by Greenness Level

Abstract

Background/Aim: The association between air pollution and depressive symptoms have been suggested in several studies. A few studies have reported that this association may be affected by greenness level. Greenness is expected to reduce air pollution and affect mental health through stress reduction, increased physical activity, noise mitigation. The objective of this study is to examine the association between long-term exposure to air pollution and depressive symptoms of 7 major cities of Korea and whether this association differs by greenness level. Methods: This study included a total of 43,104 individuals from Community Health Survey 2009. Individuals with Center for Epidemiological Studies Depression (CES-D) score ≥ 16 were classified as having depressive symptoms. District-level annual concentrations of PM10, SO2 and NO2 were obtained. To measure greenness, we used Normalized Difference Vegetation Index (NDVI) and categorized NDVI into two level: high vs low. A logistic regression was used to estimate the association between long-term exposure to air pollution and depressive symptoms. We analysed effect modification by greenness level. Results: Odds ratio (OR) of having depressive symptoms was 1.038 (95% CI: 0.971, 1.109) with interquartile range (IQR) of PM10 increase. Effect modification by greenness level was observed. In the lower greenness group, the association between exposure to PM10 and depressive symptoms was found [OR=1.206 (95% CI: 1.079, 1.349)]. In the higher greenness group, on the other hand, the association was not found [OR=0.957 (95% CI: 0.873, 1.047)]. These associations did not change when the concentration of SO2 and NO2 were adjusted. Conclusions: We found that the long-term exposure to PM10 was associated with depressive symptoms in population with lower greenness level.