Could an improvement in air quality influence mental health enough to reduce suicides? Findings from a collaborative study by researchers from the United States and China, published in Nature Sustainability, reveal that the effects of environmental conditions such as air pollution go beyond impacting physical health through chronic respiratory illnesses and can take a toll on mental health as well.

According to the researchers from University of California - Santa Barbara, China's efforts to reduce air pollution may have prevented 46,000 suicide deaths in the country over just five years.

The declining suicide rates in China compared to the rest of the world caught the attention of the study’s co-lead author Tamma Carleton, an assistant professor at UC Santa Barbara's Bren School of Environmental Science & Management. From a higher than global average in 2000, China’s per-capita suicide rate had fallen below that average two decades later – a period, which also saw air pollution levels plummeting in the country.

"It's very clear that the war on pollution in the last seven to eight years has led to unprecedented declines in pollution at a speed that we really haven't seen anywhere else," says Carleton.

Looking for a connection between the two phenomena, Carleton and co-lead author Peng Zhang, a former UCSB doctoral student, teamed up with researchers in Xanghai and Beijing, and gathered demographic data from 2013 through 2017 from the Chinese Centre for Disease Control and Prevention as well as meteorological data from the China Meteorological Data Service Centre.

Since air pollution is correlated with a lot of factors such as economic activity, commuting patterns, and industrial output among others, the researchers sought to isolate just the role of pollution on suicide. 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 allowed the researchers to isolate the effects of air pollution on suicide rates.

Comparing suicide numbers across 600 counties between weeks with inversions and those with more typical weather, the researchers found that suicide rates increased substantially when air pollution rose, especially among elderly people, with older women 2.5 times more vulnerable than other groups. Suicide rates also increased within the first week of exposure, and then abruptly declined once conditions improved, suggesting that pollution may have a direct neurologic effect, rather than creating chronic health issues that drive suicide rates up later on.

"We often think about suicide and mental health as a problem to be understood and solved at an individual level," Carleton says. "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."

She hopes the findings can reframe how society approaches suicide prevention. "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," Carleton said. "It's important that public health officials also know this as our climate gets warmer, and as pollution increases in many developing countries."

Source: University of California - Santa Barbara

Image: https://www.niehs.nih.gov/health/topics/agents/air-pollution