Air Pollution Linked to Mental Disorders Including Depression

Being exposed to air pollution could raise the risk of developing mental illnesses such as bipolar disorder and major depression, according to researchers.

A range of factors are thought to contribute to a person developing a mental illness, explained the authors of the paper published in the journal PLOS Biology. These factors include genetics, neurochemistry and the environment.

To investigate the potential link between air pollution and mental disorders, the international team of researchers looked at an insurance claims database of 151,104,811 people in the U.S., collected between 2003 and 2013. They also looked at the Danish national treatment and pollution registers, featuring information on 1,436,702 individuals born between January 1, 1979 and December 31, 2002.

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People walking in New York City on 23 May 2015. Researchers have investigated whether air pollution is linked to mental illness. Getty

Bipolar disorder and major depression were linked to air pollution in the U.S. and Denmark. In Denmark, air pollution was linked to depression, schizophrenia and personality disorder.

The data from Denmark also suggested that being exposed to poor air quality in early years raises the risk of developing bipolar disorder, schizophrenia, personality disorder, and major depression.

Co-author Andrey Rzhetsky, professor of medicine and human genetics at University of Chicago, told Newsweek: "To our knowledge, we provided the first evidence that most prevalent mental conditions are linked to pollution."

However, Rzhetsky acknowledged that the work was observational and showed a link between air pollution and mental illness, but couldn't prove it was a cause. He explained it would be unethical to conduct the sort of randomized trial needed to prove the link.

In an ideal world, argued Rzhetsky, those vulnerable to such conditions would avoid harmful levels of air pollution.

Asked what worried readers living in polluted cities can do, Rzhetsky said: "It can't possibly hurt to live in cleaner areas. Pollution is linked (by environmental researchers) to numerous diseases and increased mortality rates."

John Ioannidis, professor of medicine and health research and policy at Stanford University, wrote an article in PLOS Biology responding to the findings. He critiqued the report, arguing the U.S. data does not represent the population, and that the measures of air pollution used in each study do not capture the levels of air pollution that each person is exposed to.

Ioannidis told Newsweek: "I see this study as opening a new avenue of research. The current data need to be seen with great caution, nothing is proven yet regarding a cause-and-effect relationship between air pollution and mental disease. But the observation cannot be ignored, it needs to be pursued further and examined with additional data."

He told Newsweek the link between bipolar disorder seemed to be the strongest and most consistent across the two data sets. "I don't think I would have thought of singling out bipolar disorder in particular, before seeing the data, so this is a bit surprising. But of course, it could be no more than a correlation or a chance finding, not a causal effect."

"This research could have policy implications (e.g. regulation of air pollution) and it could change the direction of where we search for mental health causes," he said.

"Most mental health research is focusing and spending research money on biology and neuroscience rather than the environment and social/societal factors."

Responding to the article by Ioannidis, Rzhetsky said it was a "field guide for novices in observational studies, who should be warned about complexities lurking in complex datasets.

Ioannis Bakolis, a lecturer in biostatistics at King's College London who also wasn't involved in the research, told Newsweek the findings add to evidence from previous studies that link air pollution with mental disorders.

"Although there is emerging literature around the link of air pollution with depression, the link with bipolar and personality disorder is new," he said.

"Compared to other countries worldwide, Denmark has relatively low levels of pollution. This suggests that other countries have to make significant improvements to their air quality so that it is even cleaner than Denmark's to reduce potential mental health consequences of poor air quality," he argued.