A 25-year study of young adults living in the United Kingdom has found higher rates of mental illness symptoms among those exposed to greater levels of traffic-related air pollutants, particularly nitrogen oxides, during childhood and adolescence.
The World Health Organization (WHO) currently estimates that 9 out of 10 people worldwide are exposed to high levels of outdoor air pollutants, which are emitted during fossil fuel combustion in cars, trucks, and powerplants, and by many manufacturing, waste-disposal, and industrial processes.
The research, conducted by King's College London's Institute of Psychiatry, Psychology & Neuroscience (IoPPN) in the UK and Duke University in the US, has identified a link between air pollution and the risk of developing mental illnesses like depression and anxiety.
The study, published in JAMA Open Network, included 2000 twins born in England and Wales in 1994-1995 and followed them to young adulthood. They regularly participated in physical and mental health evaluations and provided information about the larger communities in which they live. The participants were also measured against their exposure to air pollutants – particularly nitrogen oxides (NOx) and fine particulate matter (PM2.5), both of which are regulated pollutants.
Participants took a mental health assessment at age 18. Symptoms associated with 10 different psychiatric disorders, including alcohol dependence, ADHD, and generalised anxiety disorder, were used to calculate a single measure of mental health, called the psychopathology factor (p-factor). The higher an individual's p-factor score, the greater the number and severity of psychiatric symptoms identified.
Over the course of the study, 22% of participants were found to have had exposure to NOx that exceeded WHO guidelines, while 84% had high exposure to PM2.5.
Those that had been exposed to greater levels of pollution had a higher p-factor score by the time they had reached 18, independent of other risk factors.
While air pollution was found to be a weaker risk factor than other more well-known risks like family history, it was still found to be as equally harmful as factors like childhood exposure to lead.
This study has demonstrated that children growing up in our biggest cities face a greater risk of mental illness due to higher levels of traffic. While we might like to think of our towns and cities as green and open spaces, it's clear that there is a hidden danger that many will not have even considered.– Dr Helen Fisher, the study's co-author and Principal Investigator from King's IoPPN
In a previous study in the same cohort, Dr Fisher linked childhood air pollution exposure to the risk of psychotic experiences in young adulthood, raising concern that air pollutants may exacerbate risk for psychosis later in life. The current study highlights that poor air quality increases the likelihood of developing a wide range of mental health problems at age 18.
We have confirmed the identification of what is essentially a novel risk factor for most major forms of mental illness, one that is modifiable and that we can intervene on at the level of whole communities, cities, and or even countries.– Aaron Reuben, first author of this study from Duke University
While the findings are most relevant to high-income countries with only moderate levels of outdoor air pollutants, like the US and the UK, there are also implications for low-income, developing countries with higher air pollution exposures, like China, Nepal, and India. "We don't know what the mental health consequences are of very high air pollution exposures, but that is an important empirical question we are investigating further," said Fisher.
This study was possible thanks to support from the UK Medical Research Council (MRC), the US National Institute of Child Health and Human Development, the US National Institute of Environmental Health Science, Google, The Jacobs Foundation; and the King's Together Multi and Interdisciplinary Research Scheme (Wellcome Trust Institutional Strategic Support Fund).
"Association Of Air Pollution Exposure in Childhood and Adolescence With Psychopathology at the Transition To Adulthood," Aaron Reuben, Louise Arseneault, Andrew Beddows, Sean D. Beevers, Terrie E. Moffitt, Antony Ambler, Rachel M. Latham, Joanne B. Newbury, Candice L. Odgers, Jonathan D. Schaefer, and Helen L. Fisher. JAMA Network Open, April 28, 2021 DOI: 10.1001/jamanetworkopen.2021.7508
