Exposure to air pollution, particularly in childhood, may raise the risk of depression and bipolar disorder, a US-led study shows.
Researchers studied health insurance data from 151 million people and found areas with the worst pollution had a 27 percent higher rate of bipolar disorder and a six percent higher rate of major depression, PLOS Biology reports.
Data from Denmark showed those growing up in the most polluted areas had a rate of schizophrenia almost 1.5 times higher than those in the least polluted areas.
But Dr Daniel Maughan of the Royal College of Psychiatrists said: "There are many environmental factors which could contribute to poor mental health for those people living in areas of high pollution. It is therefore difficult to isolate poor air quality as the cause."