Suicide accounts for more than 40,000 deaths in the US each year, making it one of the top 10 leading causes of death in the country. While psychological factors such as stress, anxiety and depression are known drivers of suicide, a new study claims to have found evidence of a more surprising risk factor: exposure to air pollution.

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People exposed to increased levels of air pollution short term – particularly men and middle-aged adults – were found to have a higher suicide risk.

The researchers, including Amanda Bakian, PhD, an assistant professor of psychiatry at the University of Utah in Salt Lake City, publish their findings in The American Journal of Epidemiology.

This is not the first study to find a link between air pollution and increased risk of suicide. A 2010 study published in The American Journal of Psychiatry found people from over seven cities in South Korea were 9% more likely to commit suicide within 2 days of a rise in air pollution.

And last year, Bakian and colleagues conducted a study that found residents of Salt Lake County were more likely to commit suicide within 3 days of being exposed to increased levels of nitrogen oxide or high concentrations of fine particulate matter (PM 2.5) – particles in smoke and haze that are 2.5 micrometers in diameter or less.

They build on these findings with their latest study, which found middle-aged individuals and men are most at risk of suicide through exposure to air pollution.

The team analyzed the records of 1,546 people in Salt Lake County who committed suicide between 2000 and 2010.

Consistent with their previous findings, the researchers calculated that individuals who were exposed to increased levels of nitrogen dioxide were 20% more likely to commit suicide in the following 3 days, while those exposed to higher concentrations of PM 2.5 were 5% more likely to take their own lives within the next 3 days.

Men were found to have an even higher risk of suicide following air pollution exposure; after exposure to increased levels of nitrogen dioxide and PM 2.5, their risk of committing suicide in the following 3 days was 25% and 5%, respectively.

For individuals aged 36-64, the researchers found that short-term exposure to high levels of nitrogen dioxide increased the risk of suicide by 20%, while short-term exposure to high concentrations of PM 2.5 was linked to a 7% increased suicide risk.

Commenting on their findings, Bakian says:

As suicide risk was found to differ by age and gender, this suggests that vulnerability to suicide following air pollution exposure is not uniform across Salt Lake County residents and that some Salt Lake County residents are more vulnerable than others.

Our next step is to determine in more detail exactly what elements – such as genetic and sociodemographic factors – are responsible for increasing one’s vulnerability to suicide following air pollution exposure.”

The researchers stress that their findings do not indicate that short-term exposure to air pollution is a direct cause of suicide. Instead, they suggest that increased air pollution may merge with other factors that drive suicide risk.

Medical News Today recently reported on a study published in The Lancet Psychiatry, which found that between 2000 and 2011, unemployment was a cause of more than 45,000 suicides worldwide each year.