Long-term exposure to low levels of air pollution could cause depression and anxiety, a study has unveiled.
Researchers from the universities of Oxford, Beijing, and Imperial College London, explored the links between air quality and mental ill-health by tracking the incidence of depression and anxiety in almost 500,000 UK adults over 11 years.
They found that those living in areas with higher pollution were more likely to suffer episodes - even when air quality was within official limits.
The researchers said their findings suggest there is a need for stricter standards or regulations for air pollution control.
The findings come as Environment Minister Thérèse Coffey has admitted the UK cannot achieve air pollution targets and has passed new guidelines that allow more than double the levels of fine particulate matter (PM2.5) than 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 confirmed its air quality level guidelines in September 2021, halving its limit for PM2.5 to five micrograms.
What did researchers find?
The researchers said how air pollution has long been linked to several respiratory disorders, but now a growing body of evidence is establishing a link with mental health disorders.
Before this new research, 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 - a large-scale biomedical database.
They modelled and gave a score to the air pollution in the areas where participants lived, including PM2.5 and PM10, nitrogen dioxide and nitric oxide.
They found 13,131 cases of depression and 15,835 of anxiety were identified among the sample within a follow-up period of about 11 years. As air pollution increased so did cases of depression and anxiety.
However, exposure-response curves were non-linear with steeper slopes at lower levels and plateauing trends at higher exposure. This suggests that long-term exposure to low levels of pollution were just as likely to lead to diagnoses as exposure to higher levels.
The researchers said they hoped policymakers would take their findings into account. They wrote: “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.”
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 lower the legal limits of air pollution.
She said: “This study provides further evidence on potential impacts of air pollution on the brain. 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.”