Ambient air pollution and suicide in Tokyo, 2001–2011

Abstract Background Some evidence suggests an association may exist between the level of air pollution and suicide mortality. However, this relation has been little studied to date. The current study examined the association in Tokyo, Japan. Methods Suicide mortality data for Tokyo for the 11-year period 2001–2011 were obtained together with data on four air pollutants: fine particulate matter (PM2.5 ), suspended particulate matter (SPM), sulphur dioxide (SO2 ) and nitrogen dioxide (NO2 ). A time-stratified case-crossover study design was used to examine the daily association between the level of air pollution and suicide mortality. Results During the study period there were 29,939 suicide deaths. In stratified analyses an interquartile range (IQR) increase in the same-day concentration of NO2 was linked to increased suicide mortality among those aged under 30 (percentage change: 6.73%, 95% CI: 0.69–13.12%). An IQR increase in PM2.5 and SO2 was associated with a 10.55% (95% CI: 2.05–19.75%) and 11.47% (95% CI: 3.60–19.93%) increase, respectively, in suicide mortality among widowed individuals for mean exposure on the first four days (average lags 0–3). Positive associations were observed for the air pollutants in the summer although associations were reversed in autumn. Limitations We relied on monitoring data to approximate individual exposure to air pollutants. Conclusions Higher levels of air pollution are associated with increased suicide mortality in some population subgroups in Tokyo. Further research is needed to elucidate the mechanisms linking air pollutants and suicide in this setting.