Exposure to air pollutants, especially small particulate matter (PM2.5 and PM10) and nitrogen dioxide (NO2), may heighten the risk of death by suicide and suicidal thoughts, suggests a pooled data analysis of the available evidence, published online in the Journal of Epidemiology & Community Health.
The findings underscore the need to consider environmental exposures as potentially modifiable risk factors in suicide prevention strategies, emphasise the researchers.
Globally, more than 720,000 people die by suicide every year, prompting the World Health Organization to develop a Mental Health Action Plan to reduce this global toll by at least a third between 2013 and 2030, they explain.
The interplay of individual, biological, and contextual factors means that suicide prevention is really a public health issue, they suggest.
But while the effect of environmental exposures on mental health outcomes, such as depression or anxiety, has been extensively studied, the potential role of environmental factors on the risk of suicide is less well understood.
To strengthen the evidence base, the researchers therefore wanted to find out whether air, noise, light, and water pollution and sociodemographic factors, such as sex and income, might influence the risk of death by suicide and suicidal behaviours.
They scoured research databases for relevant studies published in English between January 2010 and April 2024. Out of an initial haul of 287, selected for full text review, 45 met the eligibility criteria: 33 investigated death by suicide; 7 suicidal thoughts; and 5 attempted suicide.
Most studies looked at the effects of air pollution exposure (38), 3 looked at water pollution, 3 at noise pollution, and 1 at light pollution.
The results of 29 were included in a pooled data analysis; 16 were included in a narrative review, which summarises the existing evidence using text.
The pooled data analysis showed that short term exposure to PM2.5 (13 studies) and PM10 (7 studies) and long term exposure to PM2.5 (6 studies) and NO2 (7 studies) were statistically significantly associated with risk of death by suicide, attempted suicide, and suicidal thoughts.
The synthesis of evidence from the narrative review showed potential positive associations with other air pollutants, including sulphur dioxide (SO2) and ozone (O3) as well as noise pollution.
Pooled data analysis wasn't possible for the effects of water and light pollution, because of the limited number of studies and varying outcome measures; the narrative review findings for these exposures were inconsistent.
There were no clear associations between sociodemographic factors and the risk of death by suicide or suidical behaviours.
By way of an explanation for the findings, the researchers point out that air pollutants, including PM2.5, PM10, NO2 SO2, and O3 and water polluted with arsenic, lead, lithium or nitrate, have been linked to neurological effects, including chronic inflammation and nerve damage, which can impair brain function and influence mood and stress resilience.
And it has been suggested that traffic and other environmental noise and light pollution increase stress levels through disruption of the body clock, they add.
The researchers acknowledge various limitations to their findings, including the small number of studies available on each respective outcome. The included studies also varied considerably in methodology and design.
But they nevertheless conclude: "These findings bring to attention the critical importance of recognising environmental exposures as modifiable risk factors within suicide prevention efforts.
"Integrating environmental health into mental health policy, through cross-sectoral collaboration, pollution reduction strategies, and targeted public health interventions, could play a vital role in reducing suicide risk and improving overall population mental wellbeing."
