Long-term exposure to ambient air pollution and suicide risk: A national cohort in the Netherlands

Short-term exposure to ambient air pollution has been linked to an increased immediate risk of suicide. However, the relationship between long-term exposure to air pollution and suicide risk remains largely unknown. We assessed 1) the associations between long-term exposure to multiple air pollutants and suicide risk and 2) whether certain population groups are more vulnerable. We constructed a cohort of adults in the Netherlands with a follow-up from 2013 to 2018. Annual exposures to nitrogen dioxide (NO 2 ) and particulate matter (PM 2.5 , PM 10 ) were assessed based on adults’ residential history. Sex-specific hazard ratios (HRs) for the associations between air pollutants and suicide were estimated using (time-dependent) multilevel Cox regressions, including single- and two-pollutant models. Subgroup analyses were conducted by income and employment status. Among 8,712,864 adults, 2,338 women and 4,873 men died by suicide during follow-up. In single-pollutant models, time-dependent associations between PM 2.5 exposure and women’s suicide risk were non-significant from 2013 to 2017, except in 2018 (hazard ratio [HR]=1.66 per five μg/m 3 increase in PM 2.5 ; 95% confidence interval [CI]: 1.07, 2.57). This association became non-significant after adjustment for time-varying confounding by green space. Subgroup analyses indicated that the PM 2.5 -associated risk was present only among low-income women (HR=1.28 per five μg/m 3 ; 95% CI: 1.02, 1.62). No associations were observed between air pollutants and suicide risk among men across all subgroups. Associations observed among low-income women suggest that air pollution mitigation policies may be relevant for specific vulnerable populations. • Nationwide cohort of 8.7 million adults followed for suicide over six years • Annual exposure to NO 2 , PM 2.5 , and PM 10 was assessed based on residential history • Long-term exposure to NO 2 , PM 2.5 , and PM 10 showed predominantly null associations with suicide risk • An increased suicide risk was observed only for PM 2.5 among low-income women • Null associations between air pollution and suicide risk were observed among men