Long-term exposure to even comparatively low levels of air pollution could cause depression and anxiety, according to a study exploring the links between air quality and mental ill-health.
Tracking the incidence of depression and anxiety in almost 500,000 UK adults 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 Journal of the American Medical Association Psychiatry, the researchers, from the universities of Oxford and Beijing and Imperial College London, said their findings suggested a need for stricter standards or regulations for air pollution control.
The findings come as the ministers face criticism for passing new legally binding air quality guidelines that allow more than double the levels of fine particulate matter (PM2.5) than equivalent targets set by the World Health Organization.
Peers approved legislation this week that allows a maximum annual mean concentration of 12 micrograms per cubic metre by 2028. The WHO completed a review of its 2005 guideline air quality levels 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 noted, a growing body of evidence is establishing a link with mental health disorders. So far, however, the only available studies on the risk of depression were carried out in regions with air pollution concentrations exceeding UK air quality limits.
The researchers drew on the data of 389,185 participants from the UK Biobank, modelling and giving a score to the air pollution, including PM2.5 and PM10, nitrogen dioxide and nitric oxide for the areas in which they lived. They found 13,131 cases of depression and 15,835 of anxiety were identified among their sample within a follow-up period of about 11 years.
As air pollution increased, the researchers found, so did cases of depression and anxiety. Exposure-response curves were non-linear, however, with steeper slopes at lower levels and plateauing trends at higher exposure, suggesting that long-term exposure to low levels of pollution were just just as likely to lead to diagnoses as exposure to higher levels.
The researchers said they hoped policymakers would take their findings into account. “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,” they wrote.
Anna Hansell, a professor of environmental epidemiology at the University of Leicester, who was not involved in the research, said the study was yet more evidence to support a lowering of legal limits to air pollution.
“This study provides further evidence on potential impacts of air pollution on the brain,” she said. “The Committee on the Medical Effects of Air Pollution reported in 2022 on the evidence of associations between air pollution and cognitive decline and dementia. The report concluded that the link was likely to be causal.
“However, there are few studies to date on air pollution and mental health. This well-conducted new study found associations between air pollution and anxiety and depression in the UK, which experiences lower air pollution than many countries worldwide.”