Higher levels of air pollution seem to be damaging to our mental health, reports a new study from the Yale School of Public Health (YSPH).

The findings are based on six years’ worth of mental health outpatient visit data from two major hospitals in Nanjing, China. Nanjing is notorious for its high levels of air pollution, even for China (which has quite a lot of air pollution in general). After comparing the number of visits with records of particulate matter in suspension in the air every day, the authors report that visits were more numerous when air quality was especially poor.

Bad air, bad mindspace

“Here, we show that particulate matter is having these more general effects, not just on symptoms but also on service use,” says Assistant Professor Sarah Lowe, Ph.D., first author of the study.

The findings, says the team, showcase why we need further investments in mental services, especially as air pollution levels around the world are getting worse. More research is needed to understand how and why air quality influences mental health, they add, but now we know that it can influence how much use specialized services see.

Air pollution is the product of many components ranging from carbon monoxide in car exhaust to sulfur dioxide particles from industrial processes. This study focused on particulate matter (PM), tiny pieces of organic materials such as liquids or soil, which are known to pose a threat to human health. The main danger they pose comes down to their size, which allows PM to enter deep into the lungs. Once there, they can cause quite a lot of damage by ripping through lung tissue and entering the bloodstream.

The team believes that these particles can influence mental health after entering the bloodstream and reaching the brain.

“These tiny particles not only have effects on the lungs, the heart and the brain,” said YSPH Assistant Professor Kai Chen, Ph.D., senior author of the paper, “but they also have effects on other organs of your body.”

Levels of PM in Nanjing exceed the safety levels specified in China’s air-quality standards for around one in five days of the year, the team notes. As such, they expected the effect it has on psychological disorders would be reflected in an uptick of mental health visits to the city’s two hospitals.

They did see such an uptick, especially prevalent among men and older residents. This unequal distribution may come down to social and behavioral differences among people in Chinese society, but that’s just a hypothesis at this time; more data is needed to tell for sure.

What they were able to say for sure, however, is that days with worse air pollution saw more demand for outpatient mental health services. Whether one causes the other is still murky. For example, days with high levels of air pollution could limit people’s choices of activities (such as outdoor sporting events becoming unbearable or being postponed), leaving people free to come to their appointments. Alternatively, more air pollution could lead to more physical symptoms such as difficulty breathing, which would coax people into seeking mental health services in order to cope.

“There could be other reasons that we simply couldn’t explore with the data we had,” Lowe explained. “We don’t know that level of detail, and I think that would be a really interesting direction for future research,” she said.

The paper “Particulate matter pollution and risk of outpatient visits for psychological diseases in Nanjing, China” has been published in the journal Environmental Research.