Air Pollution and Suicide in 10 Cities in Northeast Asia: A Time-Stratified Case-Crossover Analysis

BACKGROUND: There is growing evidence suggesting an association between air pollution and suicide. However, previous findings varied depending on the type of air pollutant and study location. OBJECTIVES: We examined the association between air pollutants and suicide in 10 large cities in South Korea, Japan, and Taiwan. METHODS: We used a two-stage meta-analysis. First, we conducted a time-stratified case-crossover analysis to estimate the short-term association between nitrogen dioxide (NO2), sulfur dioxide (SO2), and particulate matter [aerodynamic diameter <= 10 mu m (PM10), aerodynamic diameter <= 2.5 mu m (PM2.5), and PM10-2.5] and suicide, adjusted for weather factors, day-of-week, long-term time trends, and season. Then, we conducted a meta-analysis to combine the city-specific effect estimates for NO2, SO2, and PM10 across 10 cities and for PM2.5 and PM10-2.5 across 3 cities. We first fitted single-pollutant models, followed by two-pollutant models to examine the robustness of the associations. RESULTS: Higher risk of suicide was associated with higher levels of NO2, SO2, PM10, and PM10-2.5 over multiple days. The combined relative risks (RRs) were 1.019 for NO2 (95% confidence interval [CI]: 0.999, 1.039), 1.020 for SO2 (95% CI: 1.005, 1.036), 1.016 for PM10 (95% CI: 1.004, 1.029), and 1.019 for PM10-2.5 (95% CI: 1.005, 1.033) per interquartile range (IQR) increase in the 0-1 d average level of each pollutant. We found no evidence of an association for PM2.5. Some of the associations, particularly for SO2 and NO2, were attenuated after adjusting for a second pollutant. CONCLUSIONS: Our findings suggest that higher levels of air pollution may be associated with suicide, and further research is merited to understand the underlying mechanisms.