Zhang said the impact of the environment on health and human capital was a growing area of interest in disciplines such as public health and economics.
While the focus of research has often been on physical health problems related to respiratory or cardiovascular systems such as asthma, experts have begun to realise that environmental factors can affect mental health – including suicides – as well as cognitive development.
In an interview with Phys.org, co-lead author Tamma Carleton, an assistant professor at UC Santa Barbara in the United States, said suicide rates in China had fallen much faster than in the rest of the world, while at the same time air pollution levels in China had also declined.
Why indoor air pollution matters as much as the pollution outdoors
Why indoor air pollution matters as much as the pollution outdoors
“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,” Carleton said.
The biggest challenge in the study was to quantify if – and to what extent – cleaner air led to lower suicide risks.
Zhang said that over the past two decades “advances in statistical methods in economics have made it feasible to determine whether there is a causal relationship between two related things”.
To help with their analysis, the team collected official demographic data from institutions such as the Chinese Centre for Disease Control and Prevention.
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Bangkok residents urged to work from home as air pollution reaches ‘unhealthy’ levels
Bangkok residents urged to work from home as air pollution reaches ‘unhealthy’ levels
To identify a causal effect, the researchers tried to isolate polluted days that were not related to human activity by taking advantage of an atmospheric condition known as inversion, when a warm air mass traps pollution near the Earth’s surface.
The team then correlated nearly 140,000 observations of weekly county-level suicide reports between 2013 and 2017 to a set of around 1,400 air pollution monitors across China, comparing weeks that had inversions to those with more typical weather.
“Weekly suicide rates increased immediately when air pollution worsened in that week,” Zhang said, adding that they found that older people, especially women, were more vulnerable.
The authors suggested some possible explanations for why higher PM2.5 levels might cause more people to kill themselves, including the idea that particulate matter has direct neurological effects on brain function.
Although some previous studies had uncovered a positive association between air pollution and suicides, they had been smaller in scope, for instance in a specific city, Zhang said.
Air pollution cuts lifespans in South Asia by 5 years or more: study
Air pollution cuts lifespans in South Asia by 5 years or more: study
By providing robust evidence from a nationwide analysis for the first time, he said, their findings could improve understanding in the public and the scientific community of the direct health effects from air pollution.
He said the research could also encourage policy decisions aimed at environmental improvement.
“Policymakers should consider how many lives can be saved when measuring the cost-benefits of air treatment in the future,” Zhang said.
