A decades-long study of young adults living in the UK found higher rates of mental illness symptoms in people exposed to higher levels of traffic-related air pollutants, particularly nitrogen oxides , during childhood and adolescence.
Previous studies have identified a link between air pollution and the risk of specific mental disorders, including depression and anxiety, but this study looked at changes in mental health that span all forms of disorders and psychological distress associated with exposure to traffic-related air pollutants.
The results, which will appear on April 28 in JAMA network open, reveal that the more exposure a person is to nitrogen oxides during childhood and adolescence, the more likely they are to show signs of mental illness in the transition to adulthood, at age 18, when most symptoms of mental illness have arisen or are beginning to appear.
The link between exposure to air pollution and symptoms of mental illness in young adults is modest, according to the study’s first author, Aaron Reuben, a graduate student in clinical psychology at Duke University. . But “because harmful exposures are so prevalent around the world, outdoor air pollutants could be a significant contributor to the global burden of psychiatric illness,” he said.
The World Health Organization (WHO) currently estimates that 9 out of 10 people in the world are exposed to high levels of outdoor air pollutants, which are emitted during the combustion of fossil fuels in cars, trucks and power plants, and by many manufacturers, waste disposal, and industrial processes.
In this study, air pollution, a neurotoxicant, was found to be a lower risk factor for mental illness than other better known risks, such as a family history of mental illness, but was evenly matched. other neurotoxicants known to adversely affect mental health, in particular children’s exposure to lead.
In a previous study from the same cohort, Helen Fisher of the Institute of Psychiatry, Psychology & Neuroscience at King’s College London, and co-author and principal investigator of this study, linked exposure to air pollution in children at risk for psychotic experiences in young adults, raising air pollutants can exacerbate the risk of psychosis later in life.
When combined with studies showing increased hospital admissions for many psychiatric illnesses on days of “poor” air quality in countries like China and India, the present study s’ builds on previous findings to reveal that “air pollution is likely a nonspecific risk factor for wholesale mental illness,” said Fisher, who noted that exacerbations in mental illness risk may manifest differently in different children.
The subjects of this study are a cohort of 2,000 twins born in England and Wales in 1994-1995 and followed into adulthood. They regularly participated in physical and mental health assessments and provided information on the large communities in which they live.
Researchers measured exposure to air pollutants – specifically nitrogen oxides (NOx), a regulated gaseous pollutant, and fine particulate matter (PM2.5), a regulated aerosol pollutant with fewer airborne particles. 2.5 microns in diameter – by modeling the air quality around the study. the homes of members aged 10 and 18 using high quality air dispersion models and data provided by the UK National Air Emissions Inventory and UK Road Traffic Emissions Inventory ‘Imperial College. Twenty-two percent of study members were exposed to NOx that exceeded WHO guidelines, and 84% had exposure to PM2.5 that exceeded guidelines.
The research team, based at Duke and King’s IoPPN, also assessed participants’ mental health at the age of 18. Symptoms associated with ten different psychiatric disorders – addiction to alcohol, cannabis or tobacco; conduct disorder and attention deficit hyperactivity disorder; major depression, generalized anxiety disorder, post-traumatic stress disorder and eating disorder; and symptoms of psychosis-related thinking disorders – were used to calculate a single measure of mental health, called the psychopathological factor, or “p-factor” for short.
The higher an individual’s p-factor score, the greater the number and severity of psychiatric symptoms identified. Individuals may also differ in their mental health in the subdomains of psychopathology, which include symptoms of distress or dysfunction that manifest themselves visibly from the outside (externalizing problems, such as conduct disorders), experienced mostly internally (internalizing problems, such as anxiety), and via delusions or hallucinations (symptoms of disturbed thinking). The effects of air pollution on mental health have been observed in these subfields of psychopathology, with the strongest links to symptoms of thinking disorders.
Unique to this study, the researchers also assessed the characteristics of children’s neighborhoods to account for adverse neighborhood conditions associated with higher air pollution levels and a greater risk of mental illness, including deprivation. socio-economic, physical decay, social disconnection and dangerousness. While air pollution levels were higher in neighborhoods with worse economic, physical, and social conditions, adjusting the study results to neighborhood characteristics did not change the results, nor did l ‘adjustment for individual and family factors, such as childhood emotional and behavioral issues or socioeconomic issues, mental illness status and history.
“We have confirmed the identification of what is essentially a new risk factor for most major forms of mental illness,” said Reuben, “a factor that is modifiable and that we can intervene on at the level of entire communities, cities. or even country. “
In the future, the study team is interested in learning more about the biological mechanisms that link exposure to air pollution in early life to an increased risk of mental illness during the transition to adulthood. Previous evidence suggests that exposures to air pollutants can lead to inflammation of the brain, which can lead to difficulty regulating thoughts and emotions.
While the findings are more relevant for high-income countries with moderate levels of outdoor air pollutants, such as the US and UK, they also have implications for low-income developing countries and more exposed to air pollution, such as China and India. “We don’t know what the mental health consequences of very high exposure to air pollution are, but it is an important empirical question that we are investigating further,” said Fisher.
Support for the study came from the UK Medical Research Council (MRC) [grant G1002190]; U.S. National Institute of Child Health and Human Development [grant HD077482]; U.S. National Institute of Environmental Health Sciences [grant F31ES029358]; Google; the Jacobs Foundation; a joint grant from the Natural Environment Research Council, the UK MRC and the Chief Scientist Office [NE/P010687/1]; and the King’s Together multi and interdisciplinary research program (Wellcome Trust Institutional Strategic Support Fund; grant 204823 / Z / 16 / Z).