People who were exposed to high levels of air pollution as a child may be more likely to development illness later in life, according to a new study.

The study in the journal PLOS Biology explained how researchers in the US and Denmark used insurance data from counties across America to compare incidents of mental illness to local levels of pollution.  It suggested a link between the presence of 87 types of air pollution and an increased risk of mental health problems, including bipolar disorder, schizophrenia, and personality disorders.  Counties in the bottom seventh for air quality had 27 percent higher rates of bipolar disorder.

The team then turned to data from Denmark, broken down into square kilometers and the presence of 14 different types of air pollution.  Again, those raised in the bottom seventh of air quality experienced the most mental difficulties.  That group was compared to those with the cleanest air, and the researchers found the diagnoses of bipolar disorder increased by 29 percent; schizophrenia by 148 percent; cases of depression grew by 51 percent; and personality disorder was reported 162 percent more often.

Another study released earlier this year found that children growing up in the more polluted areas of London were more likely to have depression by the age of 18 than those growing up in areas with cleaner air.

Of course, correlation does not prove causation.  But if the research proves true, it could offer hope for future generations.

"Unlike genetic predisposition, environment is something we can change," said Professor Andrey Rzhetsky, a co-author of the research at the University of Chicago.