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Small increases in people’s exposure to air pollution are linked to significant increases in depression and anxiety, according to the first study of its kind in UK adults.
The researchers found that an incremental increase in nitrogen dioxide, produced largely by diesel vehicles, increased the risk of common mental disorders by 39%. For minute particle pollution, which comes from burning fuel and brake and tire dust, the risk increased by 18%.
The scientists also found that people who lived in places with higher levels of particulate pollution were twice as likely to experience mental health problems as those who lived in the least polluted areas. The researchers recognized that other factors were important to mental health, such as genetics and childhood experiences, but added that, unlike these, air pollution could be prevented.
The study followed more than 1,000 adults in southeast London for five years, but the results are relevant for cities and towns around the world. In the UK, almost all urban areas have particulate pollution levels above the World Health Organization guidelines, and worldwide 90% of people breathe dirty air.
“Air pollution is not the only factor that can have an impact on the presence of mental disorders, but it is preventable,” said Dr. Ioannis Bakolis, a professor at King’s College London who led the research. “The introduction of measures to reduce air pollution may represent a rare and potentially impactful primary health measure for the prevention of psychiatric disorders.”
Dr Ian Mudway, a professor at Imperial College London and part of the research team, said rates of mental health disorders were known to be higher in urban areas, with suggested causes including deprivation and lack of green areas. “But what’s amazing about this study is that when you control for all those other characteristics of the urban environment and socioeconomic factors, the air pollution signal remains. It’s a very solid finding, “he added.
The World Bank has estimated that air pollution costs the world economy $ 5 trillion (£ 3.8 trillion) a year, but this includes only the known damage done to the heart and lungs by dirty air.
“Currently, there is a growing body of evidence to suggest that air pollution is not good for the brain either,” Mudway said. “In fact, we may have been minimizing the adverse effects of air pollution on our health from cradle to grave.”
Recent research has linked dirty air to an increase in suicides and indicates that growing up in polluted places increases the risk of mental disorders. Other research 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 Bakolis-led research is published in the journal Social Psychiatry and Psychiatric Epidemiology, and used standard questionnaires to assess the mental health of people in the London boroughs of Southwark and Lambeth over five years. It used data on individuals to account for factors such as age, socioeconomic status, neighborhood deprivation, and frequency of drinking, smoking, and exercise.
The research improved on previous work by estimating air pollution levels every 20 meters in the area, which means that houses on high-traffic roads can be distinguished from those on secondary streets. The study also took into account noise levels, which can be difficult to separate from air pollution because traffic influences both.
The average NOtwo levels in districts ranged from 24 to 83 micrograms per cubic meter (µg / m³), but the study found that an increase in exposure of just 3 units increased the risk of common mental disorders by 39%. Small particle contamination ranged from 9 to 23 µg / m³, and an increase of 5 units increased the risk of mental health problems by 18%.
Epidemiological studies cannot prove a causal link between air pollution and mental health problems, and scientists cannot experiment on people. But a wide range of psychiatric conditions have been linked to inflammation in the body, including the brain, and recent work has shown that tiny air pollution particles lodged in the brain are associated with molecular damage.
The latest study is important and takes into account a long list of other factors that can affect mental health, said Professor Antonio Gasparini, from the London School of Hygiene and Tropical Medicine. But he said the broad definition of mental health used made it difficult to assess possible causal links. “More studies are needed before offering [health] recommendations, “he added.
Professor Anna Hansell from the University of Leicester said the research was interesting and was done with care. He also said that more studies using different statistical techniques are needed to confirm the findings.
“However, there are already urgent reasons to reduce air pollution because of its association with chronic disease and premature death,” Hansell said. He added that regular exercise, even in polluted places, benefits physical and mental health.
“People should act, not just worry,” Bakolis said. The evidence of damage from air pollution is now strong enough that people should ask their elected representatives for more action, he added.
Mudway, who is raising a young family in central London, said she walked as much as possible and chose less polluted routes.
