Ambient air pollution and suicide in Tokyo, 2001-2011

- Higher air pollution might be associated with an increased risk for suicide.
- However, the suicide-air pollution relation has been little researched to date.
- We examined the effects of air pollution on suicide mortality in Tokyo, 2001-2011.
- PM2.5, NO2 and SO2 were linked to suicide mortality in certain population subgroups.
- Air pollution may exacerbate the risk of suicide in vulnerable individuals.

BackgroundSome 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.MethodsSuicide 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.ResultsDuring 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.LimitationsWe relied on monitoring data to approximate individual exposure to air pollutants.ConclusionsHigher 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.