Air pollution takes a massive toll on our health. The World Health Organisation links it to deadly diseases like lung cancer and stroke, and new research suggests that polluted regions see more cases of neurological disorders like depression and bipolar disorder, National Geographic reports.

In the United States, scientists found counties with the worst air quality, as indicated by the Environmental Protection Agency, had a 27 percent increase in bipolar disorder and 6 percent increase in depression, when compared to the national average.

Study author and University of Chicago geneticist Andrey Rzhetsky is careful to note that the study doesn’t definitively prove air pollution causes mental illness, but he says it shows where a person might be slightly more at risk.

Similar studies in London, China, and South Korea have similarly found a link between polluted places and poor mental health.

Rzhetsky says their study shows that where U.S. counties are being polluted, neurological disorders are taking a toll.