Your Car’s Exhaust Could Be Hurting Children’s Mental Health

Long-term exposure to air pollution, and particularly car exhaust, may contribute to childhood mental health problems, according to a new study of prescriptions given to more than half a million Swedish children.

“There may be a link between exposure to air pollution and dispensed medications for certain psychiatric disorders in children and adolescents even at the relatively low levels of air pollution in the study regions,” concluded researchers from Umeå University in Sweden, whose findings were published on June 3 in the medical journal BMJ Open.

Previous studies have found an association between air pollution and mental health in adults, including depression, anxiety, and stress, while studies in children have found links to cognitive disabilities and disorders such as autism.

For this study, the investigators looked at a national register of prescriptions among 552,221 children and adolescents under 18 in four Swedish counties between 2007 and 2010 and compared them with measured concentrations of particulates as well as nitrogen dioxide, a byproduct of vehicle combustion, in their respective neighborhoods.

They found that for every 10 micrograms per cubic meter of nitrogen dioxide, the likelihood that children were prescribed medication for at least one psychiatric diagnosis increased by 9 percent. The group of drugs prescribed included antipsychotic medications, sedatives, and sleeping pills.

The risk remained steady even after socioeconomic and demographic factors were taken into account.

“This is a very broad or crude marker of mental health,” said lead author Anna Oudin, a researcher in the Department of Public Health and Clinical Medicine at Umeå University. “We can’t say if one of the medications in that group drove the association of all of them, but it’s sort of a hint that there’s something there.”

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The prescription records did not include antidepressants or drugs to treat attention deficit hyperactivity disorder. “This study was based on data that was already available,” Oudin said. “We are applying for permission from the authorities to look at those drugs as well.”

While air pollution is more common in urbanized areas, the findings did not establish that urban environments were more likely to cause mental disorders. Three of the counties in the study have relatively high population densities, while the fourth is a largely rural county in the north of Sweden.

“The fact that we found this effect in low-density areas doesn’t support the idea that this is due to an urban environment,” Oudin said.

A sub-analysis of children living only in urban areas also found a correlation between increased nitrogen dioxide levels and drug prescriptions, suggesting that pollution rather than city life was the contributing factor.

“We did not have data on traffic-related noise or access to green environments,” Oudin said. “So maybe those things could explain it, but we can’t say that for sure.”

Michelle Block, an associate professor of anatomy and cell biology at Indiana University who has researched the impact of pollution on immune cells in the brain, said this large population study from Sweden corroborates much of what she has seen in the lab.

Air pollution, Block said, is made of toxic gases, metals, and other compounds.

“Some of those will reach the brain and can cause neuro-inflammation,” she said. “Psychiatric disorders have been linked to neuro-inflammation, so there’s an implication of a link with pollution, although it’s indirect evidence.”

Block called the study “a good paper in a good journal and with a large cohort. It’s something that people are going to pay attention to.”

“We’re going to see these types of studies explode because it’s such a new field,” she added. “So when these things happen, for the field, it’s a big deal.”