According to a new study, people who live in a heavily polluted area have a higher risk of depression and anxiety than those who live with cleaner air.
The study, published Wednesday in the journal JAMA Psychiatry, found that people exposed to higher amounts of several air pollutants over a long period of time – including particulate pollution, nitrogen dioxide and oxides of nitrogen – had an increased risk of depression and anxiety.
Particulate pollution, also known as particulate matter, is the mixture of solid and liquid droplets floating in the air, according to the US Environmental Protection Agency. It can take the form of dirt, dust, soot or smoke. Coal and natural gas 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 by-products. Nitrogen oxides are also released by traffic, as well as by the burning of oil, coal and natural gas.
The smallest particulate matter included in the new study, PM2.5, is so small – 1/20th the width of a human hair – that it can pass through your body’s usual defenses.
Instead of being carried out when you exhale, it can get stuck in your lungs or enter your bloodstream. The particles cause irritation and inflammation and can lead to respiratory problems. Exposure can cause cancer, stroke or heart attack; it could also worsen asthma, and it has long been linked to a higher risk of depression and anxiety.
For the new study, researchers looked at the records of 389,185 people from the UK 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 greater risk of depression and anxiety, even when pollution levels were below UK air quality standards.
The risk of anxiety related to PM2.5 pollution was higher in men than in women.
The study can’t determine the reason for this overall link, but others have found that exposure to air pollution can affect the central nervous system, causing inflammation and damaging cells in the body.
According to studies, certain types of air pollution can also cause the body to release harmful substances that can damage the blood-brain barrier, the network of blood vessels and tissues made up of closely spaced cells that protect the brain, and which can lead to anxiety and depression. But more research will be needed to fully understand this link, as the neural basis of anxiety and depression is not fully understood.
Other studies have shown that pollution can affect the onset of anxiety and depression, said Dr. Marianthi-Anna Kioumourtzoglou, associate professor of environmental health sciences at Columbia’s Mailman School of Public Health. She was not involved in the new research, but has done similar work on the association between exposure to air pollution and depression.
“There have been several studies that show that air pollution is also associated with an exacerbation. So, for example, if there is air pollution today and yesterday, we see an increase in our hospital admissions for these disorders,” Kioumourtzoglou said.
She and her colleagues have also found links to other neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease.
“The link between air pollution and the brain is now quite consistent in the literature,” Kioumourtzoglou said.
Limitations of the new research include a lack of information on 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 some diseases, there is still a lot of work to do,” said Kioumourtzoglou.
The study authors hope the research will encourage policy makers to do what they can to reduce exposure to pollution.
“Since the air quality standards of many countries are still well above the latest World Health Organization 2021 Global Air Quality Guidelines, stricter standards or regulations for the control pollution should be implemented in future policymaking,” the authors wrote.