Exposure to air pollution may be associated with an increased risk of developing bipolar disorder and depression, according to a study.
Researchers at the University of Chicago in the US suggest a significant link between exposure to environmental pollution and an increase in the prevalence of neuropsychiatric disorders.
"Our studies in the US and Denmark show that living in polluted areas, especially early in life, is predictive of mental disorders," said computational biologist Atif Khan, the first author of the new study published in the journal PLoS Biology,.
"These neurological and psychiatric diseases -- so costly in both financial and social terms -- appear linked to the physical environment, particularly air quality," Khan said.
Khan and Andrey Rzhetsky, a professor at Chicago used a US health insurance database of 151 million individuals with 11 years of inpatient and outpatient claims for neuropsychiatric diseases.
They compared the geo-incidence of claims to measurements of 87 potential air pollutants from the US Environmental Protection Agency (EPA).
The counties with the worst air quality had a 27 per cent increase in bipolar disorder and six per cent increase in major depression when compared to those with the best air quality.
The team also found a strong association between polluted soil and an increased risk of personality disorder.
Because these correlations seemed unusually strong, the team sought to validate their findings by applying the methodology on data from another country.
The team collaborated with Denmark-based researchers 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.
The associations the team found, especially for bipolar disorder, mirrored those in the US: a 29 per cent increase for those in counties with the worst air quality.
Using this more specific Danish data, the team found early childhood exposures correlated even more strongly with major depression (a 50 per cent increase); with schizophrenia (a 148 per cent increase); and with personality disorders (a 162 per cent increase) over individuals who grew up in areas with the highest quality air.
Researchers have long suspected that genetic and neurochemical factors interact at different levels to affect the onset, severity and progression of these illnesses.
So far, scientists have found only modest associations between individual genetic variants and neuropsychiatric disease.
For most common polymorphisms, disease risk increase is small, perhaps less than 10 per cent.
This fact led Rzhetsky to look for other molecular factors that might trigger or contribute to the disease mechanism.
The team worked on the project for over two years, enhancing their models with additional mathematical analyses and data sources.
However, other researchers in the field have noted that this substantial correlation still does not confirm pollution actually triggers the diseases.
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.