Research led by the University of Chicago and based on analysis of large population data sets from the United States and Denmark suggests a "significant link" between pollution and mental health disorders in the two countries.

The study, which is the latest to link poor air quality with ill-health, used a US health insurance database of 151 million people with 11 years of inpatient and outpatient claims for neuropsychiatric diseases.

Researchers then compared the "geo-incidents" of claims to measurements of 87 potential air pollutants.

The study, published in PloS Biology, found that counties with the worst air quality had a 27 per cent increase in bipolar disorder and a 6 per cent increase in major depression when compared with those with the best air quality.

The UChicago team applied the same methodology to data from Denmark to validate its findings.

In collaboration with Denmark-based researchers Aarhus, they examined the incidence of neuropsychiatric disease in Danish adults living in areas with poor environmental quality up to their 10th birthdays.

The team found there was a 29 per cent increase in mental health disorders for people living in counties with the worst air quality.

By using the Danish data, the team also found that early childhood exposure correlated even more strongly with major depression, schizophrenia, and personality disorders over individuals who grew up in areas with the highest quality air.

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

Dr Daniel Maughan, associate registrar for sustainability at the Royal College of Psychiatrists, said the study built on the "increasing evidence" of a link between air pollution and the development of mental illness.

He said that, while the study does not show that air pollution causes mental illness, it "suggests" a "strong link" exists between early exposure and an increased risk of developing mental ill-health.

Dr Maughan added: "However, there are many environmental factors which could contribute to poor mental health for those people living in areas of high pollution - such as population density and diminished access to green spaces - so it is therefore difficult to isolate poor air quality as the cause of mental illness."

Australian Associated Press