Associations between air pollution, income inequality, and death from suicide
Creators: Steele, Brian J
Publisher: name: University of Alberta Library
Year: 2024

<p>Background. In 2019, suicide was the second-leading cause of death among Canadians aged 18-35 and the ninth-leading cause of death for all Canadians. Environmental air pollution has been associated with respiratory, neurological, cardiovascular, oncological, and psychiatric health conditions. Short term exposures to air pollution have been linked to suicide attempts and deaths, but there is less evidence of the association with long-term exposures. </p>

<p>Income inequality, a measure of the distribution of income within an area, may elevate mental ill-health symptoms contributing to suicide. Income inequality is hypothesized to negatively impact mental health by increasing awareness of social rank and reducing social cohesion.  While studies have explored the joint effects of area-level inequality and pollution on health, few studies have examined the relationship between pollution and psychiatric conditions. </p>

<p>Understanding these associations has relevance for Canadian public health, as the potential for both rising inequality from a changing social environment and the potential for increased environmental air pollution from a changing physical environment could increase risks for health conditions that, in turn, increase the risk for suicide-related behaviors. </p>

<p>Objective. This research aimed to estimate the association between air pollution, area-level income inequality, and suicide deaths among Canadian adults. It was hypothesized that air pollution and area-level income inequality would be independently associated with greater hazards of death from suicide. It was also hypothesized that area-level income inequality and air pollution may have a positive multiplicative interaction on the hazard of death by suicide.</p>

<p>Methods. This study used a retrospective cohort design with national, population-level data. Participants in the 2006 Canadian Census Health and Environment Cohorts (CanCHECs) with residential mobility (postal code) data were followed from July 1, 2006 to June 30, 2017. Suicide deaths were obtained from in the Canadian Vital Statistics Database. </p>

<p>Environmental exposure data was provided at the postal code level by the Canadian Urban Environmental Health Research Consortium. Particulate matter at or below the 2.5-micron level (PM2.5) and ozone (O3) were assigned at the postal code level included as time-varying lagged exposures. Estimates for area-level income inequality (the Gini coefficient of after-tax household income) and relevant area-level covariates were assigned at baseline using data from the 2006 Census.</p>

<p>Cox-proportional hazard models were fit with cluster-robust standard errors to estimate the hazard of suicide, with baseline hazards stratified by sex, age, and income adequacy.<br>
Interactions were tested between income inequality and particulate matter. Sensitivity analyses were conducted to compare single- and multipollutant models with and without the inclusion of temperature as an area-level covariate, varied cluster-levels (individual-level, area-level, and none).</p>

<p>Results. The analytic sample included 1,588,340 Canadian adults who contributed 16,754,215 years of person-time over the follow-up period. There were 104,450 observed deaths (6.6% of the sample), 2,790 of which were suicides (0.2%). In multipollutant models adjusted for area-level clustering, an interquartile range (IQR) increase in PM2.5 exposure (2.73 µg/m3) was significantly associated with increased relative hazards for suicide (adjusted hazard ratio: 1.27, 95% CI: 1.08 – 1.51). Log hazard plots displayed non-linear but positive associations between PM2.5 and suicide. Results were inconsistent for ozone. In fully adjusted models, IQR-level increases in Gini (0.0316 units) were not associated with statistically significant increases in adjusted relative hazards. </p>

<p>Conclusion. As the effects of anthropogenic climate change intensify, ambient air pollution is expected to increasingly affect population health. The results of this study suggest that long-term pollution exposures may contribute to the public health burden of suicide mortality.</p>