Long-term exposure to even relatively low levels of air pollution can cause depression and anxiety, according to a study examining links between air quality and mental health.
Tracking the incidence of depression and anxiety in almost 500,000 adults in the UK over 11 years, researchers found that those living in areas with higher pollution were more likely to suffer episodes, even when air quality was within official limits .
Writing in the American Medical Association’s Journal of Psychiatry, researchers from Oxford and Peking Universities and Imperial College London said their findings suggest a need for stricter standards or regulations to control air pollution.
The findings come as ministers face criticism for adopting new legally binding air quality guidelines that allow more than twice the levels of fine particulate matter (PM2.5) of equivalent targets set by the World Health Organisation.
The partners approved legislation this week allowing a maximum annual average concentration of 12 micrograms per cubic meter until 2028. The WHO completed a review of its 2005 air quality level guidelines in September 2021, halving its limit for PM2.5 to five micrograms.
Air pollution has long been implicated in a number of respiratory disorders, but, the researchers note, increasing evidence is establishing a link to mental disorders. However, to date the only studies available on the risk of depression have been conducted in regions with air pollution concentrations exceeding UK air quality limits.
The researchers used data from 389,185 UK Biobank participants to model and estimate air pollution, including PM2.5 and PM10, nitrogen dioxide and nitrogen oxide, for the areas where they lived. They found that 13,131 cases of depression and 15,835 of anxiety were identified among their sample over a follow-up period of about 11 years.
Researchers found that as air pollution increased, so did incidences of depression and anxiety. However, the exposure-response curves were non-linear, with steeper slopes at lower levels and plateau trends at higher exposure, suggesting that long-term exposure to low levels of pollution is as likely to lead to diagnoses as and exposure to higher levels.
The researchers said they hope policymakers take their findings into consideration. “Given that air quality standards in many countries are still well above the latest World Health Organization global air quality guidelines for 2021, stricter standards or regulations to control air pollution should be implemented in future policy development,” they write.
Anna Hansel, professor of environmental epidemiology at the University of Leicester, who was not involved in the research, said the study was further evidence to support the lowering of legal limits on air pollution.
“This study provides further evidence of the potential impact of air pollution on the brain,” she said. “The Committee on the Medical Effects of Air Pollution reports in 2022 on evidence of links between air pollution and cognitive decline and dementia. The report concludes that the relationship is likely causal.
“However, to date there have been few studies on air pollution and mental health. This well-conducted new study found links between air pollution and anxiety and depression in the UK, which experiences lower air pollution than many countries around the world.