There is a ‘significant link’ between exposure to air pollution in childhood and developing mental illnesses such as bipolar disorder, schizophrenia and depression later in life, according to a new study.

Much is now known about the dangers of air pollution to our physical health but there is now a growing body of evidence that suggests that air pollution may be harming the human brain.

Researchers from the University of Chicago analysed population data sets from both the United States and Denmark for the study, which was published in PLoS Biology.

They used a U.S. health insurance database of 151 million people with 11 years of inpatient and outpatient claims for mental illnesses.

They then compared the location of these claims to measurements of 87 potential air pollutants from the United States Environmental Protection Agency.

They found that the US counties with the worst air quality had a 27% increase in bipolar disorder and a 6% increase in major depression when compared to those with the best air quality.

Because these US-based findings seemed ‘unusually strong’ the researchers decided to apply the methodology on another country, choosing Denmark.

The team in Chicago 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 mental illness in Danish adults who had lived in areas with poor environmental quality up to their tenth birthdays.

The results, especially for bipolar disorder, mirrored those in the United States, showing a 29% 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% increase); with schizophrenia (a 148% increase); and with personality disorders (a 162% increase) over individuals who grew up in areas with the highest quality air.

The researchers said that while the study didn’t address the question of how air pollution might trigger mental illness, a large body of experimental studies in animal has suggested that pollutants affect neuroinflammatory pathways and set the stage for neurodevelopmental problems later in life.

Speaking to AirQualityNews, a spokesperson for UK-based mental health charity Rethink Mental Illness said: ‘There are some limitations in this study, in that it doesn’t take into account all of the factors that we know affect our mental health, but the findings from this initial research are very interesting.

‘While the effects of air pollution on our physical health have long been recognised, this research adds weight to the argument that improving the quality of the air we breathe would benefit both our mental and physical health, in addition to improving the environment we live in.’

This year there have been several studies exploring the link between exposure to air pollution and mental health.

In January, a groundbreaking study found that happiness levels on social media decline during periods of high air pollution.

Another study published in May suggested a link between transport-related air pollution and childhood anxiety.

Photo Credit – Pixabay