People who live in a highly polluted area have a higher risk of depression and anxiety than those who live with cleaner air, a new study says.The study, published Wednesday in the journal JAMA Psychiatry, found that people who were exposed to higher amounts of multiple air pollutants for a long period — including particle pollution, nitrogen dioxide and nitrogen oxides — had an increased risk of depression and anxiety.Particle pollution, also known as particulate matter, is the mix of solid and liquid droplets floating in the air, the U.S. Environmental Protection Agency says. It can come in the form of dirt, dust, soot or smoke. Coal- and natural gas-fired power plants create it, as do cars, agriculture, unpaved roads, construction sites and wildfires.Nitrogen dioxide pollution is most commonly associated with traffic-related combustion byproducts. Nitrogen oxides are also released from traffic, as well as the burning of oil, coal and natural gas.The smallest particulate matter included in the new study, PM2.5, is so tiny — 1/20th of a width of a human hair — that it can travel past your body's usual defenses.Instead of being carried out when you exhale, it can get stuck in your lungs or go into your bloodstream. The particles cause irritation and inflammation and may lead to respiratory problems. Exposure can cause cancer, stroke or heart attack; it could also aggravate asthma, and it has long been associated with a higher risk of depression and anxiety.For the new study, researchers looked at the records of 389,185 people from the U.K. Biobank, a large-scale biomedical database of half a million diverse volunteers. During the study period, 13,131 were diagnosed with depression and 15,835 were diagnosed with anxiety.Those who lived in areas with higher pollution levels were at higher risk for depression and anxiety, even when the pollution levels were below U.K. air quality standards.The risk of anxiety linked to PM2.5 pollution was stronger in men than in women.The study can't pinpoint the reason for the overall link, but others have found that exposure to air pollution may affect the central nervous system, causing inflammation and damaging the body's cells.Some air pollution, studies show, can also cause the body to release harmful substances that can hurt the blood-brain barrier, the network of blood vessels and tissues made up of closely spaced cells that protect the brain, and that may lead to anxiety and depression. But more research will be needed to fully understand this connection because the neural basis for both anxiety and depression is not completely understood.Other studies have found that pollution can affect the onset of anxiety and depression, said Dr. Marianthi-Anna Kioumourtzoglou, an associate professor of environmental health sciences at Columbia's Mailman School of Public Health. She wasn't involved in the new research but has done similar work on the association between air pollution exposure and depression."There have been several studies that show that air pollution is also associated with exacerbation. So for example, if there's air pollution today and yesterday, then we see an uptake in our hospital admissions for these disorders," Kioumourtzoglou said.She and her colleagues have also found links with other neurodegenerative diseases like Alzheimer's and Parkinson's."The link between air pollution and the brain has now been pretty consistent in the literature," Kioumourtzoglou said.The limitations of the new research include a lack of information about other common air pollutants like ozone, carbon monoxide or sulfur dioxide."Not all air pollutants are created equal. Some are more toxic than others. And for certain diseases, there's still a lot of work to be done," Kioumourtzoglou said.The study authors hope the research will encourage public policy-makers to do what they can to reduce exposure to pollution."Considering that many countries' air quality standards are still well above the latest World Health Organization global air quality guidelines 2021, stricter standards or regulations for air pollution control should be implemented in the future policy making," the authors wrote.