Exposure to high levels of air pollution increases a person's risk for depression and adversely affects problem-solving and other brain functions, a study published Monday by the Proceedings of the National Academy of Sciences found.
The analysis of 352 healthy adults living in Beijing, China, a city with significant air pollution, found that those exposed to large amounts of particulate matter, or PM2.5, exhibited more symptoms of depression.
Study participants exposed to PM2.5, which are microscopic dust particles and other pollutants, also reported more difficulties with problem-solving and other mental tasks, the data showed.
In addition, magnetic resonance imaging, or MRI, screenings of the study participants revealed that those exposed to high levels of PM2.5 showed evidence of disruption in activity in 22 brain regions, including those involved in thinking and memory, the researchers said.
"Air pollution not only affects heart and lung health, it can directly affect the operation of genes in the brain that control thinking and emotional functions that can lead to brain disorders like depression," study co-author Dr. Hao Yang Tan told UPI in an email.
"The nuance of this is that while any air pollution is bad, for people with genetic risk for depression, the effects on brain function and ultimately risk for depressive illness are much worse," said Tan, lead investigator at the Lieber Institute for Brain Development at Johns Hopkins University in Baltimore.
About 90% of the global population lives in regions with air pollution levels above the thresholds for human health established by the World Health Organization, the international agency estimates.
Fine particulate matter such as PM2.5 has been linked with up to 4 million early deaths worldwide annually and has been described as "the greatest threat to human health."
Although most of the health complications related to air pollution are associated with the heart and lungs, there is evidence that it can also affect mental health, with a study published earlier this year suggesting that worker productivity is impacted in offices with poor air quality.
For this study, Tan and his colleagues assessed 352 otherwise healthy adults living in Beijing for symptoms of depression using standard diagnostic criteria.
Study participants also answered questionnaires on mental health and brain function throughout the course of the study.
In addition, they also underwent genetic testing to establish their risk for depression based on family history, according to the researchers.
The researchers estimated each participant's PM2.5 exposure in the six months immediately before the study using data from the nearest air monitoring station to their residential address.
Participants were also asked to solve several mathematical problems while being timed and undergoing functional MRI scanning, which measures brain activity during the performance of certain tasks.
Study participants living in areas with higher PM2.5 levels based on monitoring station data had more symptoms of depression and showed greater evidence of compromised brain performance on functional MRI, according to the researchers.
Those with a genetic risk for depression based on genotyping more than one million DNA variants, who were also exposed to high levels of PM2.5 were at higher risk for the disorder compared with those without a genetic history, the data showed.
"These findings are likely the tip of the iceberg in terms of the genes and brain functions involved," Tan said.
"While we focus on depression, it is likely other related disorders from ADHD, to anxiety disorders, to perhaps even psychosis and dementia may be implicated," he said.