Air pollutant exposure, especially to small particulate matter 2.5 (PM_2.5) and PM₁₀, is associated with increased risk for suicide outcomes, new research suggested.

A meta-analysis and review of 45 studies showed that short-term exposure to PM₁₀, long-term exposure to nitrogen dioxide, and short- and long-term exposure to PM_2.5 were all significantly linked to elevated risk for suicidal ideation, attempted suicide, and death by suicide.

Although positive associations with these outcomes were observed for the air pollutants of sulphur dioxide (SO₂) and ozone (O₃) and for noise pollution, they were not statistically significant, investigators noted, adding that evidence was inconclusive for water and light pollution.

Still, the findings “highlight the importance of considering environmental exposures as modifiable risk factors in suicide prevention,” Sophie Marie Jones, PhD, Centre for Public Health at Queen’s University Belfast, Belfast, Northern Ireland, and colleagues wrote.

The results were published online on September 15 in the Journal of Epidemiology & Community Health.

Overlooked Subject

While previous research has linked environmental pollutants to psychiatric illness, researchers noted that less was known about the effect on suicide risk.

The systematic review and meta-analysis included 16 studies in a narrative review and 29 in a meta-analysis, conducted in the US, South Korea, China, Taiwan, Belgium, Spain, and Italy.

Other single and multicountry studies were conducted in Denmark, Switzerland, Poland, Hungary, the UK, Sweden, France, Netherlands, Germany, Austria, and Colombia.

Air, noise, light, and water pollution were assessed for possible associations with suicide and suicidal behaviors.

At less than 6 months of exposure, pooled results showed a small, but significant, increased risk for suicide, attempted suicide, and suicide ideation per 10 ug/m³ increase in PM_2.5 (odds ratio [OR], 1.0139; P = .048) and per 10 ug/m³ increase in PM₁₀ (OR, 1.010; P = .036).

For more than 6 months of exposure, the risk for all three outcomes was 53% higher for each 10 ug/m3 increase in PM_2.5 (OR, 1.525; P = .005) and 32% higher for each 10 parts per billion increase in nitrogen dioxide (OR, 1.317; P = .0114).

In the narrative review, associations were not statistically significant for SO₂, O₃, and noise pollution.

Findings from the narrative review on water pollution were inconclusive, while a meta-analysis for this factor could not be conducted due to heterogeneity. 

While a meta-analysis of light pollution associations could not be conducted because of the small number of available studies, a narrative review did suggest a positive link to the outcomes. 

Together, the results show that incorporating environmental factors into psychiatric policies “could play a vital role in reducing suicide risk and improving overall population mental well-being,” the investigators wrote.

‘Provides Support’ But With Caveats

In a statement to the UK nonprofit Science Media Centre, Rosie Cornish, MSc, Epidemiology and Health Data Science at the University of Bristol, Bristol, England, noted that the observed associations found in the study could be explained by factors other than air pollution, including lifestyle, green space availability, and socioeconomic deprivation. 

“If air pollution is not actually a cause of increased risk of suicide, then reducing pollution will not help to prevent suicide. The authors do not acknowledge this when drawing their conclusions,” said Cornish, who was not involved with the research.

In the same statement, Jon Van Niekerk, MBChB, MS, chair of the Royal College of Psychiatrists’ General Adult Faculty, noted that the review adds to previous research that suggested links between some air pollution exposures and suicidal behavior at the population level.

“However, it is important to be mindful that most of the underlying evidence is observational and so this study cannot establish that air pollution itself causes suicidal thoughts or attempts,” he said.

Van Niekerk also agreed with Cornish that other factors, such as physical health and urban living, may have influenced the findings; and he pointed out that the measures used for both pollution exposure and suicidal behavior varied widely between the studies that were included.

“The study provides further population-level support for reducing harmful air pollution, though the findings should not be seen as supporting individual suicide-risk prediction or suggesting that pollution reduction alone could be a suicide-prevention measure,” Van Niekerk concluded.

The study was funded by a UK Prevention Research Partnership grant and the Queen’s University Belfast. The investigators, Cornish, and Van Niekerk reported no relevant financial relationships.