Cutting air pollution could benefit millions of people: Air pollution linked to more severe mental illness

London: Exposure to air pollution is linked to an increased severity of mental illness, according to the most comprehensive study of its kind.

The research, involving 13,000 people in London, found that a relatively small increase in exposure to nitrogen dioxide led to a 32% increase in the risk of needing community-based treatment and an 18% increase in the risk of being admitted to hospital.

The researchers said the findings were likely to apply to most cities in developed nations, and cutting air pollution could benefit millions of people. “Air pollution is modifiable, and on a big scale as well, reducing population-level exposure,” said Joanne Newbury, of the University of Bristol, part of the research team. “We know there are interventions that can be used, such as expanding low-emission zones. Mental health interventions at the individual level are actually quite difficult.”

The study used the frequency of admission to hospital or visits to community doctors and nurses as a measure of severity. The researchers calculated that a small reduction in one pollutant alone could reduce illness and save the NHS tens of millions a year.

Levels of air pollution in London have fallen in recent years but there is no safe level, said Ioannis Bakolis, of King’s College London, who led the research. “Even at low levels of air pollution, you can observe this kind of very important effect.” Recent research has shown that small increases in air pollution are linked to significant rises in depression and anxiety.

It has also linked dirty air to increased suicides and indicated that growing up in polluted places increases the risk of mental disorders. Other research has found that air pollution causes a “huge” reduction in intelligence and is linked to dementia.

A global review in 2019 concluded that air pollution may be damaging every organ in the human body. The new study, published in the British Journal of Psychiatry, tracked patients in south London from their first contact with mental health services and used high-resolution estimates of air pollution at their homes.

The quarterly average NO2 levels in the study area varied by between 18 and 96 micrograms per cubic metre (µg/m³). The researchers found that people exposed to 15µg/m³ higher levels of pollution had an 18% higher risk of being admitted to hospital and a 32% higher risk of needing outpatient treatment after a year.

The link was strongest for NO2, which is largely emitted by diesel vehicles, but was also significant for small particle pollution, which is produced by burning all fossil fuels. The small particle levels varied from 9 to 25 µg/m³ and an increased exposure of 3 units increased hospital admission risk by 11% and outpatient treatment risk by 7%.

The scientists assessed the patient data again seven years after the first treatment and found the link to air pollution was still apparent. The findings were not explained by a range of possible other factors including age, sex, ethnicity, deprivation or population density, although unidentified factors might still play an important role.