The quality of air can influence a person's mental health, according to the results of a new study. The research indicates a causal connection between air pollution and suicide rates, suggesting that initiatives to improve air quality can decrease suicide deaths.

Researchers from India and the U.S. who conducted the study found that suicide rates increase substantially when air pollution rises and the effect was particularly strong in the elderly, with older women 2.5 times more at risk than other groups. The study also estimated that China's measures to reduce air pollution in the country have successfully averted 46,000 suicide deaths over five years.

There is an established link between air pollution and physical health issues and increased risk of a spectrum of conditions, including asthma, cardiovascular disease, and lung cancer. However, according to Tamma Carleton, the study's co-lead author, these environmental factors can take a toll on mental health as well.

"We often think about suicide and mental health as a problem to be understood and solved at an individual level. This result points to the important role of public policy, of environmental policy, in mitigating mental health and suicide crises outside of individual-level intervention," Carleton said in a news release.

Carleton previously studied the impact of temperature on suicide rates in India and observed a correlation where elevated temperatures led to increased suicide rates. When she and co-lead author Peng Zhang noticed a more rapid decline in suicide rates in China compared to the global average, they decided to explore the connection between the country's recent efforts to combat air pollution and the observed decrease in suicide rates.

To conduct their study, the researchers collected demographic data from the Chinese Center for Disease Control and Prevention between 2013 and 2017. Additionally, they obtained meteorological data from the China Meteorological Data Service Center. The primary challenge in their research was separating the impact of pollution on suicide rates from other correlated factors such as economic activity, commuting patterns, and industrial output.

"To this aim, they took advantage of an atmospheric condition called an inversion, where warm air traps a layer of cold air beneath it like a lid on a pot. This can concentrate air pollution near the surface, leading to days with higher pollution levels that aren't correlated with human activity. This relatively random phenomenon enabled Carleton, Zhang and their co-authors to isolate the effects of air pollution on suicide rates," the news release stated.

By decoupling pollution levels from human activity, which inherently influences human behavior, the researchers could establish a causal effect between air pollution and suicide rates.

They then compared the number of suicides across 600 counties, distinguishing between weeks with inversions and those with more typical weather, and analyzed the data using a statistical model.

The analysis indicates that the impact of pollution was notably pronounced among the elderly, with older women being 2.5 times more vulnerable compared to other groups.

However, the authors are unsure why older women are particularly susceptible to the impact of pollution on mental health, but cultural factors may play a role. A significant proportion of suicides among women in China are associated with acute crises, and if pollution has an immediate impact on mental health, it could disproportionately affect older women, researchers noted.

"And the phenomenon does appear to happen relatively quickly. Rates increase within the first week of exposure, and then abruptly decline once conditions improve. This suggests that pollution may have a direct neurologic effect, rather than creating chronic health issues that drive suicide rates up later on. Indeed, there is growing evidence that particulate pollution affects neurochemistry," the news release added.

Apart from air pollution, several environmental factors could influence suicide rates, Carleton explained. "Thirty years of warming in India led to about the same magnitude of suicide effects as about five years of air pollution control in China," the author said.

"Public policy about air pollution — something you can't control, what's outside your window — is affecting the likelihood that you take your own life. And I think that puts a different lens on the solutions we should be thinking about. It's important that public health officials also know this as our climate gets warmer, and as pollution increases in many developing countries," Carleton added.

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