The study, which looked at 13,000 people in south London since they started using mental health services, found the link between air pollution and the severity of mental illness was strongest for nitrogen dioxide (NO2), a pollutant largely emitted by diesel vehicles.
In the study area, average quarterly NO2 concentrations ranged from 18 to 96 μg/m³. The team found that people exposed to pollution concentrations greater than 15μg/m³ had an 18% higher risk of hospitalization and a 32% higher risk of needing outpatient treatment after one year.
The team re-evaluated the patients’ data seven years later and found the association with air pollution was still strong. The findings could not be explained by factors such as age, gender, ethnicity, poor living conditions or population density, although these unidentified factors may still play a role.
Although the study did not focus on proving a causal link between air pollution and the severity of mental illness, the team said the link is “biologically plausible,” as air pollutants have potent inflammatory properties, and inflammation is thought to be a factor in mental disorders.
Several recent studies have also shown that increased air pollution has a significant impact on the increase of depression and anxiety. In addition, dirty air has been linked to increased suicide rates; growing up in polluted areas increases the risk of mental disorders. Several other studies have found that air pollution causes a sharp decline in intelligence and is linked to dementia. A 2019 global review concluded that air pollution can harm every organ in the human body.
The findings could be applied to most cities in developed countries, and cutting air pollution could benefit millions of people, the team says.
