Study links air pollution to severity of mental illness

A study of 13,000 people in London concluded that exposure to polluted air can exacerbate mental illness. British investigators reviewed medical data, from the first contacts with the health services, to pollution levels in residential areas. They believe the link between polluted air and mental damage is “biologically plausible”.

Nitrogen dioxide, also known as nitrogen dioxide – NO2 – is recognized as one of the main pollutants circulating in the atmosphere. It comes from fossil fuels like oil or coal. It is burned at high temperatures in car engines and in the industrial sector, turns into toxic gases and is emitted into the air we breathe.

Risks to human health have been demonstrated, especially in respiratory and lung diseases.

The new British study, published by the University of Cambridge, assesses the potential mental health severity associated with exposure to polluted air.

In the work, the researchers say, “Evidence suggests that exposure to air pollution can negatively affect the brain and increase the risk of psychiatric disorders such as schizophrenia and depression. However, little is known about the potential role of air pollution in the severity and subsequent relapse of the disease.”

Scientists tracked patients in south London and benchmarked the pollution associated with their homes.

Average NO2 levels in the study area ranged between 18 and 96 micrograms per cubic meter (µg/m3) every three months. The researchers found that individuals exposed to 15 mcg/m3 of contamination had an 18% higher risk of being hospitalized and a 32% higher risk of needing outpatient treatment after one year.

The relationship with nitrogen dioxide became clearer when the levels of small particles ranged from 9 to 25 μg/m³, resulting in a threefold increase in exposure, increasing the risk of hospitalization by 11% and the risk of outpatient treatment by 7%.

The study revealed that patient data assessed seven years after the first treatment maintain an association with air pollution.

For the scientists, “home exposure to polluted air is associated with increased use of mental health services among people newly diagnosed with psychotic and mood disorders.”

The researchers estimated that “reducing the exposure of city dwellers in the UK to pollution by small particles, by just a few units, up to the WHO’s annual limit of 10 μg/m3” would have an impact on mental health services. There could be a 2% cut and tens of millions of pounds would be saved annually.

The study authors highlight that “identifying modifiable risk factors for disease severity and relapse can aid early intervention efforts, and reduce human suffering and significant economic costs caused by chronic, long-term mental illness.”

Kevin McConway, a professor at the Open University, is not part of the team that signs up for the study, but gives a positive assessment of the work.

“This is a good study. The statistical analysis is generally appropriate and increases confidence that there are at least some elements of cause and effect in the association between pollution and mental health,” says McConway, quoted in the British publication guardian.

“But it is not easy for people to avoid pollution,” he adds. “Reducing air pollution in cities requires large-scale societal actions.”

The World Bank estimates that air pollution costs the global economy billions of dollars, but it only includes heart and lung disease.