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There is no doubt that air pollution is bad for human health. It is a major risk factor for cardiovascular disease and is an enormous risk factor for morbidity and mortality worldwide. More recently, a growing body of research shows air pollution can also have detrimental impacts on the brain

A new study tracked a cohort of over 2,000 individuals in the United Kingdom throughout childhood and adolescence to discover links between mental health and pollution. The long-term study found higher rates of symptoms related to mental illnesses like depression and schizophrenia in those exposed to fine particulates and nitrogen oxides from cars, factories, and power plants. 

Aaron Reuben, a clinical psychology doctoral student at Duke University and study author, says researchers recognized a potential link between exposure to pollutants and brain health back in the 1990s. Studies over the past two decades have shown some alarming connections between fine particulate matter, also known as PM2.5, and cognitive decline, which could lead to dementia. 

[Related: Tiny air pollutants may come from different sources, but they all show a similar biased trend.]

This new study uses longitudinal data from a cohort of children born in England and Wales who have regularly participated in health evaluations from birth throughout childhood until they reached adulthood. Scientists evaluated the mental health of the participants when they reached age 18. 

“We asked them about symptoms across 10 important mental disorders, so things like depression, anxiety, psychosis, alcohol dependence,” Reuben says. Then the researchers took this data and used it to calculate one number called a “psychopathology factor,” which would be higher if the person had more mental health issues. When comparing exposure to environmental pollutants throughout childhood to the test results, the researchers found higher rates of mental illness symptoms in those exposed to the most pollution throughout their youth.

Interestingly, the impact of air pollution didn’t lead to one specific type of mental health issue. “It doesn’t seem to target any one brain function, but actually, it leads to overall dysregulation that manifests in greater rates of mental illness across all diagnostic categories,” he says. However, the highest effects were on thought disorders like psychosis.

Children that grew up in areas with high rates of nitrogen oxides in their neighborhoods from ages 10 to 18 struggled the most once they reached adulthood. “Nitrogen oxides were the most strongly implicated in our findings,” Reuben says, “but we can’t say if that was necessarily, you know, nitrogen oxides themselves, or other things related to traffic emissions that come alongside nitrogen oxides.” 

This may, Reuben says, “help explain a long term trend that we’ve known about for many years, which is that people who live in cities tend to be at greater risk of schizophrenia and psychosis.”

[Related: Living in the same city doesn’t mean breathing the same air.]

Of course, pollution isn’t the only thing that can affect a person’s mental health. But when corrected for other factors, like family history and neighborhood environment characteristics, the data still stood, Reuban says. 

“None of our results changed when we made these high-quality adjustments,” he says. “That makes us pretty confident that what we’re seeing is actually a unique independent effect of air pollution on the development of mental health problems.” 

While scientists know that air pollution can harm the brain, the mechanisms for the harm are still elusive. There is some evidence, Reuben says, that pollution traveling through the nose to the brain can have a direct impact on the brain. “But it seems that even greater contributors are probably what we call systemic inflammation,” where small pollutants invade the lungs and cause a “cascade of inflammatory actions that then seem to reach the brain and cause inflammation.” Research has shown that the body’s immune response causes inflammation, which may then be linked to mental illnesses such as depression and bipolar disorders, but this needs more examination in the future.

Reuben says this study shows that even in areas such as the UK (which barely breaks the top 100 most polluted countries in the world), people are feeling the mental strain of pollution. More research must be done on the young residents of other countries, like China and India, with locations that suffer even greater amounts of pollution. 

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