Higher levels of air pollution may correspond to higher rates of mental health disorders in kids and teens, according to a new study conducted in Sweden.

Researchers found that, in areas with higher levels of pollution, there were more medications dispensed for psychiatric conditions in children and teens, compared with areas with lower levels of pollution.

"The results can mean that a decreased concentration of air pollution — first and foremost, traffic-related air pollution — may reduce psychiatric disorders in children and adolescents," lead study author Anna Oudin, a public health researcher at Umeå University in Sweden, said in a statement.

In the study, the researchers looked at a national registry in Sweden that lists all medications for psychiatric disorders, such as antipsychotics and certain sedatives, that were dispensed to children and teens in four Swedish counties between 2007 and 2010. The researchers also examined data on air pollution levels in these four counties (the counties were Stockholm, Västra Götaland, Skåne and Västerbotten). [11 New Warning Signs Help Spot Mental Illness in Children]

The researchers found that the higher the levels of air pollution, the higher the rate of medications dispensed for psychiatric conditions in children and teens. Specifically, the rate of medications increased by 9 percent with every 10 microgram per cubic meter increase in nitrogen dioxide.

The new findings add to previous research that has shown links between air pollution and anxiety, perceived levels of stress and mental health conditions in the general population, the researchers said in their study, published June 3 in the journal BMJ Open.

It is not clear how air pollution may affect people's mental health, but it could be that air pollution leads to inflammation and oxidative stress, which in turn may contribute to mental health problems, the researchers said. Some research has also suggested that the brain is vulnerable to ambient particulate matter in polluted air, the researchers said.

However, the new study does not show that there is a cause-and-effect relationship between air pollution and psychiatric disorders, said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City, who was not involved in the study. [5 Controversial Mental Health Treatments]

The association between increased pollution levels and increased levels of dispensed medications for such disorders could also have been explained by other factors such as the high prevalence of the mood disorder called seasonal affective disorder (SAD) in Scandinavian countries such as Sweden, he said.

More research is needed to rule out other factors that could be behind the link shown in the study, Horovitz told Live Science.

Originally published on Live Science.

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