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Exposure to air pollution linked with increased mental health service-use

A study supported by researchers at King’s College London has found that exposure to traffic-related air pollution is associated with increased mental health service-use among those recently diagnosed with psychotic and mood disorders.

Increased use of mental health services reflects mental illness severity, suggesting that initiatives to lessen air pollution could improve outcomes for those with these disorders and reduce costs of the healthcare needed to support them.

London bus

Researchers at King’s College London, University of Bristol and Imperial College London analysed data from 13,887 people aged 15 years and over who had face-to-face contact with South London and Maudsley NHS Foundation Trust services between 2008 and 2012. Individuals were followed from the date of their first face-to-face contact for up to seven years.

In 2019, 119,000 people lived with illegal levels of polluted air in London. Previous research lead by the World Health Organisation has found that adults exposed to high levels of traffic-related air pollution are more likely to experience common mental health disorders such as anxiety and mild depression. However, prior to this study little was known about whether air pollution exposure contributes to the course and severity after the onset of more serious mental illness.

To collect the required data, anonymised electronic mental health records were linked with models that identify the concentrations of air pollutants at the residential address of the participants. These included nitrogen dioxide and nitrogen oxides (NO2 and NOx) and fine and coarse particulate matter (PM2.5 and PM10), which are the key pollutants known to have an impact on health.

Findings from this research

The study found people exposed to higher residential levels of air pollutants used mental healthcare services more frequently in the months and years following their initial presentation to secondary mental healthcare services compared to those exposed to lower air pollution.

The researchers found that for every three micrograms per cubic meter increase in very small particulate matter (PM2.5) and 15 micrograms per cubic meter increase in nitrogen dioxide (NO2) over a one-year period there was an increased risk of having an inpatient stay of 11% and 18%. Results also showed increases in PM2.5 and NO2 were associated with a 7%t and 32%increased risk of requiring community-based mental healthcare for the same period. These findings were also replicated over a seven-year period.

Dr Ioannis Bakolis, Senior Lecturer in Biostatistics and Epidemiology at the Institute of Psychiatry, Psychology & Neuroscience, King’s College London and lead author of the study, said:

There is already evidence linking air pollution to the incidence of mental disorders, but our novel findings suggest that air pollution could also play a role in the severity of mental disorders for people with pre-existing mental health conditions.
Our research indicates that air pollution is a major risk factor for increased severity of mental disorders. It is also a risk factor that is easily modifiable which suggests more public health initiatives to reduce exposure such as low emission zones could improve mental health outcomes as well as reduce the high healthcare costs caused by long-term chronic mental illness.

According to the researchers, if the UK urban population’s exposure to PM2.5 was reduced by just a few units to the World Health Organisation’s recommended annual limit (10 micrograms per cubic metre), this would reduce usage of mental health services by around 2%.  

Dr Joanne Newbury, Sir Henry Wellcome Research Fellow, Bristol Medical School, and the study’s first author, added:

We now plan to examine whether air pollution is associated with a broader range of mental health, neurodevelopmental, and educational outcomes, particularly among children, who might be especially vulnerable to air pollution.

South London and Maudsley NHS Foundation Trust provides comprehensive secondary mental healthcare to approximately 1.36 million people within the London boroughs of Croydon, Lambeth, Lewisham and Southwark. These are inner-city areas with high-traffic flows and high average air pollution concentrations compared to other UK urban areas that reflect London’s diversity in terms of ethnicity and wealth.

The researchers controlled the analyses for several potential variables that could influence the association between air pollution and service-use association, such as deprivation, population density, age, season, marital status and ethnicity. However, they cautioned that the study does not prove cause and effect, and further research is needed to demonstrate exactly how air pollution might increase severity of mental health problems.

Dr Adrian James, President of the Royal College of Psychiatrists, said:

The environmental and climate emergency is also a mental health emergency. Our health is fundamentally linked to the quality of our environment, whether that's about cleaner air, access to green spaces or protection from extreme weather.
If air pollution is exacerbating pre-existing serious mental illnesses, such as schizophrenia, bipolar disorder and major depression, then improving air quality could reduce the pressure on mental health services. As we look ahead to our post-pandemic future, it is vital that we find ways to build back greener and prevent poor health. This important research presents a clear example where these go hand-in-hand.

The research was funded by the National Institute for Health Research (NIHR), the NIHR Maudsley Biomedical Research Centre, the Wellcome Trust, the Economic and Social Research Council, and the UK Medical Research Council.

The paper ‘Association between air pollution exposure and mental health service use among individuals with first presentations of psychotic and mood disorders: retrospective cohort study’ was published in the British Journal of Psychiatry.

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