Newswise – Researchers in the United States and China have discovered a strange connection between air pollution and suicide rates that has us rethinking how we deal with the problem. China’s efforts to reduce air pollution have prevented 46,000 suicide deaths in the country in just five years, researchers estimate. The team used weather conditions to tease apart confounding factors affecting pollution and suicide rates, arriving at what they believe is a truly causal relationship. The results, published in Sustainability in nature, Discover air quality as a key factor in mental health.
Issues such as air pollution are often viewed as a physical health problem, leading to a range of acute and chronic diseases such as asthma, cardiovascular disease and lung cancer. But co-lead author Tamma Carleton, an assistant professor at UC Santa Barbara’s Bren School of Environmental Science & Management, knows that these environmental factors can also affect mental health. she is previously studied examined the influence of temperature on suicide rates in India and found that excessive heat drives up these rates. That’s why she was curious when she noticed that the rate in China was falling much faster than in the rest of the world. In 2000, the country’s per capita suicide rate was above the global average; Two decades later, it has fallen below that average, which itself is declining.
At the same time, air pollution fell. “It’s very clear that the war on pollution over the last seven to eight years has led to an unprecedented decline in pollution at a pace that we really haven’t seen anywhere else,” Carleton said. Perhaps these two phenomena are related, Carleton thought.
Carleton and co-lead author Peng Zhang, a former UCSB graduate student, teamed up with researchers in Xanghai and Beijing to study the impact of China’s recent crackdown on air pollution on suicide rates across the country. They collected demographic data from 2013 to 2017 from the Chinese Center for Disease Control and Prevention and meteorological data from the China Meteorological Data Service Center.
The team faced a tricky task.
“One of the bigger challenges with previous work on this problem is that air pollution is related to many things,” Carleton said. For example, economic activity, commuting behavior and even industrial production are correlated with environmental pollution. And these activities can also influence suicide rates. “Our goal was to isolate just the role of pollution in suicide, as opposed to all the other things that might be related to air pollution.”
To do this, they took advantage of an atmospheric condition called inversion, in which warm air traps a layer of cold air underneath, similar to a lid on a pot. This allows air pollution to concentrate near the surface, resulting in days with higher levels of pollution that are not related to human activity. This relatively random phenomenon allowed Carleton, Zhang and their co-authors to isolate the effects of air pollution on suicide rates. By decoupling pollution levels from human activity – which influences human behavior – the authors believe they have actually identified a causal effect.
The team compared suicide rates in 600 counties between weeks with inversions and those with more typical weather and ran the data through a statistical model. “Suicide rates increase significantly as air pollution increases,” the authors noted. The effect was particularly strong among older people, with older women 2.5 times more at risk than other groups.
The authors are unsure why older women are particularly susceptible to this effect, although it may be partly cultural. Previous research suggests that most female suicides in China result from acute crises. So if pollution has an acute impact on mental health, it could disproportionately affect older women.
And the phenomenon seems to happen relatively quickly. Rates increase within the first week of exposure and then decline abruptly as conditions improve. This suggests that pollution may have a direct neurological effect, rather than causing chronic health problems that later drive up suicide rates. In fact, there is increasing evidence that particulate matter pollution affects neurochemistry.
Pollution isn’t the only environmental factor affecting suicide rates, but Carleton said it’s a major concern. “Thirty years of warming in India resulted in about the same level of suicide effects as about five years of air pollution control in China,” she explained.
“We often view suicide and mental health as an issue that needs to be understood and resolved on an individual level,” she continued. “This finding points to the important role of public policy and environmental policy in alleviating mental health and suicide crises, going beyond individual-level interventions.”
She hopes the results can redefine society’s approach to suicide prevention. “Public policy around air pollution – something you can’t control that’s outside your window – influences the likelihood of you taking your own life. And I think that puts a different perspective on the solutions we should be thinking about,” Carleton said. “It is important that health authorities also know this as our climate becomes warmer and pollution increases in many developing countries.”
Carleton plans to take a closer look at suicide rates in other Southeast Asian countries. Most suicide research has been conducted in the United States and Europe, she explained. It is less clear what is driving suicide in the developing world, where we are also seeing the most rapid environmental change.
Of course, pollution is not the only factor that can cause a person to end their life. “About 10% of the overall decline over the last five years is due to particulate matter pollution,” Carleton said. “This is important, but it also means that 90% of cases cannot be explained by pollution.”
There are many reasons to control pollution around the world and now suicide can be added to the conversation. China’s aggressive, successful policies achieved dramatic results in a short period of time, serving as a potential model for other countries struggling with pollution and helping to reshape the conversation about suicide in the modern world.