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A new study, led by the University of Chicago, has found that people raised in areas with high levels of air pollution show a definite link to increased risk of developing psychological conditions such as depression, schizophrenia and bipolar disorder.

The research, based on a US health insurance database of 151 million individuals with 11 years of inpatient and outpatient claims for neuropsychiatric illnesses, found a “significant link” to counties with the highest levels of air pollution, noting a 50% increase in diagnoses of major depression, a 148% increase in schizophrenia, and a 27% increase in bipolar disorder, as well as a 6% rise in major depression when compared to areas with the best air quality.

Researchers also found a “strong association” between polluted soil, and increase in the risk of developing a personality disorder.

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According to the University of Chicago release: "Because these correlations seemed unusually strong, the team sought to validate their findings by applying the methodology on data from another country. Denmark tracks environmental quality indicators over much smaller areas (a little over one-quarter of a mile) than does the EPA. The UChicago team collaborated with Denmark-based researchers Aarhus to analyse Danish national treatment registers with data from 1.4 million people born in Denmark between 1979 and 2002. The researchers examined the incidence of neuropsychiatric disease in Danish adults who had lived in areas with poor environmental quality up to their tenth birthdays.

Atif Khan, first author of the study and a computational biologist at the University of Chicago said: “Our studies in the United States and Denmark show that living in polluted areas, especially early in life, is predictive of mental disorders.

“These neurological and psychiatric diseases – so costly in both financial and social terms – appear linked to the physical environment, particularly air quality.”

Andrey Rzhetsky, the Edna K. Papazian Professor of Medicine and Human Genetics and the paper’s senior author has been studying the genetic roots of a wide variety of neuropsychiatric diseases for over two decades, to look for other molecular factors that might trigger or contribute to the disease mechanism.

Other researchers in the field have, however, noted this substantial correlation still does not confirm pollution actually triggers the diseases.

Rzhetsky adds that in experiments on animals exposed to pollution, the animals show signs of cognitive impairment and depression-like behavioural symptoms.

While the study did not address the question of how air pollution might trigger neural effects, a large body of experimental studies in animal models suggests that polluting chemicals affect neuroinflammatory pathways and set the stage for later neurodevelopmental problems—many of which occur at the end of childhood as children become adults.