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 (NO2) and particulate matter (PM2.5, PM10) 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 PM2.5 exposure and women's suicide risk were non-significant from 2013 to 2017, except in 2018 (hazard ratio [HR] = 1.66 per five μg/m3 increase in PM2.5; 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 PM2.5-associated risk was present only among low-income women (HR = 1.28 per five μg/m3; 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.