Research consistently shows a link between urban living and psychotic disorders, with individuals raised in urban settings approximately twice as likely as those in rural areas to develop such disorders in adulthood. However, little is known about the role of the urban environment in subclinical psychotic experiences, such as hearing voices that others cannot hear and intense feelings of paranoia, explains Joanne B. Newbury, PhD. With emerging evidence linking air pollution to mental health problems but none examining the potential link between air pollution and psychotic experiences, Dr. Newbury and colleagues investigated whether psychotic experiences are more common among teenagers exposed to high levels of air pollution, and whether air pollution levels might also contribute to the link between urban living and early psychotic experiences.

For a study published in JAMA Psychiatry, the researchers linked high-resolution annualized estimates of four outdoor air pollutants—nitrogen dioxide (NO2), nitrogen oxides (NOx), particulate matter with a diameter of less than 2.5 micrometres (PM2.5), and particulate matter with a diameter of less than 10 micrometers—to the addresses of E-Risk study participants at age 17. At age 18, the participants were privately interviewed about psychotic experiences.

“We found that psychotic experiences were significantly more common among adolescents exposed to the highest quartile of NO2, NOx, and PM2.5, after controlling for a range of potential confounders and neighborhood factors,” says Dr. Newbury. “Teenagers exposed to the highest levels of NO2, NOx, and PM2.5 had 71%, 72%, and 45% greater odds, respectively, for psychotic experiences compared with those with lower exposure.” The study team found that NO2 and NOx statistically mediated around 60% of the association between urban living and adolescent psychotic experiences.

Dr. Newbury notes that whether the associations seen in the study are causal remains to be determined, adding that they may be due to noise pollution from heavy urban traffic. “It is therefore too early to make recommendations about clinical implications of our findings,” she says. “However, our findings add to the body of evidence linking air pollution to physical health problems and to emerging evidence linking air pollution to mental health problems.”