Recently, scientists from the United States and Denmark showed that the risk of mental illness depends on air quality. This supports the hypothesis that more and more people in the world suffer from mental disorders and neurological diseases, including due to the environment.
Neurotoxins in the air
The last two decades have seen a sharp increase in the number of mental disorders and autism. This is very alarming and at the same time requires an explanation.
In part, the epidemic of mental illness is attributed to better diagnostics and a larger population with access to medicine. But mainly efforts have been concentrated on finding hereditary causes. Many groups of genes have been found with mutations that significantly increase the risk of mental illness. However, long-term observations of twins do not allow completely attributing the occurrence and development of these conditions to genetics. Scientists are inclined to conclude that a complex combination of hereditary, social and environmental factors plays a role here.
Scientists have long noted that in large cities the proportion of people with mental disorders is higher than in rural areas. This prompted attention to air quality.
For example, in 2013, American scientists analyzed data on more than seven thousand children born with autism spectrum disorder to women who, while pregnant, lived in Los Angeles. Experts mapped air monitoring data and residential addresses. It was found that ozone and toxic particle pollution less than 2.5 micrometers increases the risk of autism by 12-15 percent. The risk increases by nine percent for pollution with nitrogen oxides and dioxides.
By 2014, six results of controlled trials had been published that linked autism to urban air quality. But what is its mechanism? One of the possible explanations is provided by the work of scientists from the University of Rochester School of Medicine (USA). They put the rodents every day for the first two weeks and months of their life in an area filled with the same polluted air that occurs during rush hour on the streets of an average city. Then they examined their brains and found out that all the experimental subjects showed signs of inflammation, and the lateral ventricles are sometimes enlarged three times compared with the norm, the white body in them has not fully developed. The level of the neurotransmitter glutamate is increased in the nervous tissue. Such changes are typical for people with autism and schizophrenia.
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The authors of the work believe that the smaller the particles of pollutants in the air, especially those of carbon origin from fuel combustion, tire wear, the more chances they have to enter the brain through the respiratory tract. And then the immune system acts against them, causing inflammation. Over time, it becomes chronic and damages the central nervous system.
Air pollution with nitrogen dioxide and particulate matter (right) in London in 2007. The map was compiled by scientists from the Institute of Psychiatry and clinics in the UK and USA. Their pilot analysis showed that the risk of getting mental problems at the age of 18 is higher for those who spent the first years of their lives in the most polluted areas of the city.
Risks are higher in cities
In China, the air quality problem is particularly acute. One of the most recent studies was published by scientists from Peking University and Tsinghua University. They monitored about twenty thousand residents of 25 provinces across the country. People were asked to rate their mental well-being from 2010 to 2014: scientists were interested in the frequency of depression, nervousness, and upset.
It turned out that mental well-being most strongly depends on smog, where there are many ultrafine toxin particles (less than 2.5 micrometers in size), and fluctuations in daytime temperature.
Finally, the largest study to find the link between ecology and mental illness was presented at the end of August by scientists from the University of Chicago (USA) and Aarhus University (Denmark). They relied on data on 151 million claims in the United States from 2003 to 2013 and 1.4 million patients born in Denmark from 1979 to 2022 and lived there for the first ten years of life.
To complete the picture, in the United States, scientists also assessed the contribution of social factors, such as access to health insurance, income, population density, and origin (heredity) - were the ancestors from Europe or Africa, or were they Native Americans.
The highest risk of developing major depression is found in Europeans. Schizophrenia and epilepsy are more common in African Americans. The risk of bipolar disorder rises 27 percent in counties with poor air quality compared to the national average. Poor quality land increases the risk of personality disorder by 19.2 percent.
The results for Denmark are that people who grew up in the country's most polluted areas had a 162 percent higher risk of personality disorder, 148 percent higher risk of schizophrenia and 29.4 percent higher risk of bipolar disorder. And although these results cannot be directly compared with the American ones, the trend is noticeable.
The problem is that it is still impossible to prove a causal relationship between air pollution and mental disorders: there are too many other harmful factors and stresses surrounding urban residents. As for the mechanism of such a connection, the authors of the study cite three hypotheses, which ultimately boil down to oxidative stress in brain cells and, as a consequence, their suppression, death and damage to the genetic material.
Background, social factors and ecology are associated with mental disorders. Air quality is most strongly correlated with bipolar disorder.
Tatiana Pichugina