Exposure to Air Pollution May Increase Your Risk of Depression

Science has increasingly shown that genes play a big part in someone's risk of developing depression. Now, researchers have also found that when people with those genes are exposed to high levels of air pollution, their risk for developing depression increases exponentially.

They found that air pollution, in people who were predisposed to depression, caused changes in the brain circuits. These circuits are responsible for key functions usually associated with depression, such as logical thinking and emotional processing, according to the new study published in Proceedings of the National Academies of Sciences.

“The key finding here is that air pollution does indeed affect our mental health," Hao Yang Tan, MD, a Lieber Institute researcher and author of this study, told Verywell. "And for those who are at genetic risk, the impact of pollution on mental health and brain function is greatly magnified.”

Yang Tan points out that, although researchers have suspected for a while that air pollution could be responsible for mental conditions, it hadn’t been clear how, and why, until now.

For some time, researchers hypothesized whether air pollution actually neurologically affected depression or if it was a case of socioeconomic factors, like living with more stress and physical illness.

"We find that air pollution affects genes controlling these functions in the brain, and for the people with versions of these genes that predispose them to depression, air pollution has a much larger, magnified, multiplicative effect on these problem solving and emotional control brain processes," Yang Tan said.

These findings help pave the way for how scientists and policymakers across the globe understand the depth of air pollution’s effects on our physical and mental health.

The Link Between Depression and Pollution

Researchers have identified over 170 genes that can determine who's at a greater risk of developing depression. These genes, however, are turned on and off by environmental triggers.

Which genes are turned on and off, when and for how long all make up an individual’s “phenotype,” or a person's observable traits. It’s not a given that a genetic predisposition for depression means you'll develop the condition.

The neuroscientists at the Lieber Institute for Brain Development and Peking University in Beijing wanted to see how much air pollution, as an environmental factor, affects the way genes display depression. They used a combination of surveys, genetic studies, and neuroimaging technology in order to answer this question.

They started by conducting their research on a cohort of more than 350 adults living in Beijing, one of the most polluted cities in the world. First, the researchers genetically profiled the participants, figuring out how likely they would be to suffer from depression in the future based solely on their genes. They assessed a total of 49 depression-associated genes.

Second, they collected information about how much air pollution participants had been exposed to in the past. Specifically, this was accounted for in the form of what scientists call particulate matter, tiny inhalable particles smaller than 2.5 microns, like the pollution from car exhaust. They tracked this for the six months prior to the study, with results from air pollution monitoring stations closest to participants' homes.

Then, researchers had the participants carry out cognitive tests while undergoing MRI scans in order to have a visual picture of which parts of the brain were most stimulated and responsible for their performance in the exercises. During the test, they were also given some unexpected negative feedback to create situations of stress.

“We studied the neurological functions most connected to depression, so thinking functions, problem-solving functions, all those that are dysfunctional in people with depression who cannot concentrate, cannot think clearly, and regulate emotions,” Yang Tan said.

Researchers then used brain imaging to measure the functioning of those 49 genes, measuring how exposure to air pollution turned them on and off.

"Given that this was the first-of-its-kind study, it should be considered a foundation," Jagdish Khubchandani, a professor of public health at New Mexico State University who was not involved in this research, told Verywell. "The novelty here is the brain imaging and all the complicated testing. This is a humongous effort and despite the small sample size in a limited region, the number of tests and assessments make this study unique and an idea that should be explored further."

The results showed that, in the participants with a high genetic risk of depression and high exposure to air pollution, those core brain functions are, indeed, different. Therefore, depression was much more likely for people who already have that genetic predisposition, especially if they are exposed to high levels of air pollution.

“In addition to cutting short lives, you know, from lung cancer and heart attack, air pollution can make life very miserable for quite a lot of people,” Yang Tan said.

The same brain connections that are responsible for exacerbating those depression genes are in the prefrontal cortex. This part of the brain also plays a role in other mental conditions so the effect of air pollution might be even broader. 

“It is likely that air pollution also directly affects genes related to these important brain functions that relate not just to depression, but to perhaps everyday life and also probably overlapping with other brain disorders as well,” Yang Tan said.

What's Next?

Findings like these could be helpful for scientists and policymakers all over the world. Densely populated urban areas suffer the most from air pollution. These are also the places where socioeconomic inequality is the greatest.

“A lot of this work rings alarm bells and has been ringing bells for a while now,” Yang Tan said. “90% of the world's population are exposed to unhealthy hair. So it's ubiquitous. It’s two sides of the same coin with climate change. And so it's going to be with us for a while."

Researchers and policymakers need to find ways to help people in the time it will take to tackle these pollution issues, according to Yang Tan.

For example, Yang Tan suggests medical settings start implementing genetic testing for depression to create a profile of patients and help intervene early for people in need.

“With these genes, we can potentially work out medications or vitamins or other nutritional supplements or something that could reduce the impact of air pollution on some of these vulnerable individuals,” Yang Tan said.

Looking forward, replicating this study with more diverse subjects would be helpful, according to Steven Pratt, MD, senior medical director at Magellan Health, who was not involved in the study.

“Beijing has one of the highest levels of air pollution in the world, and it is unclear to what extent we would find the same results with lower levels of pollution,” Pratt told Verywell. "What chemicals make up the pollution in Beijing might be different from other places."

"On a social scale, we should address emissions as a public policy strategy," Pratt added. Employers, businesses, and building designers could all help by addressing indoor air quality through air exchange and filtration systems, Pratt suggested, which are, after all, the same modifications that are used to address the pandemic.

“As we learn more about mental illness, depression, and mental well-being we find that we need to address whole-person solutions,” Pratt said. “It is not just a matter of taking an antidepressant medication or seeing a therapist but also eating healthy, exercising, managing stress, having social connections and, now we can add to that, doing what we can to improve the quality of the air we breathe.”