A new study led by University of Chicago researchers finds an association between exposure to environmental pollution and an increase in the prevalence of neuropsychiatric disorders.
Based on analysis of large population data sets from both the United States (151 million unique individuals) and Denmark (1.4 million unique individuals), the open-access study, published in PLoS Biology, found pollution associated with increased rates of bipolar disorder and major depression in both countries.
For the US cohort, the team studied 4 psychiatric and 2 neurological conditions: bipolar disorder, major depression, personality disorder, schizophrenia, epilepsy, and Parkinson disease. For the Danish cohort, the team studied study 4 psychiatric disorders: bipolar disorder, schizophrenia, personality disorder, and depression.
Our studies in the United States and Denmark show that living in polluted areas, especially early in life, is predictive of mental disorders. These neurological and psychiatric diseases—so costly in both financial and social terms—appear linked to the physical environment, particularly air quality.—computational biologist Atif Khan, PhD, first author
Khan and Andrey Rzhetsky, PhD, Edna K. Papazian Professor of Medicine and Human Genetics and the paper’s senior author, used a US health insurance database of 151 million individuals with 11 years of inpatient and outpatient claims for neuropsychiatric diseases. They compared the geo-incidence of claims to measurements of 87 potential air pollutants from the United States Environmental Protection Agency (EPA).
The counties with the worst air quality had a 27% increase in bipolar disorder and 6 percent increase in major depression when compared to those with the best air quality. The team also found a strong association between polluted soil and an increased risk of personality disorder.
Because these correlations seemed unusually strong, the team sought to validate their findings by applying the methodology on data from another country.
Denmark tracks environmental quality indicators over much smaller areas (a little over one-quarter of a mile) than does the EPA. The UChicago team collaborated with Denmark-based researchers Aarhus to analyze Danish national treatment registers with data from 1.4 million people born in Denmark between 1979 and 2002. The researchers examined the incidence of neuropsychiatric disease in Danish adults who had lived in areas with poor environmental quality up to their tenth birthdays.
These neurological and psychiatric diseases appear linked to the physical environment, particularly air quality.
The associations the team found, especially for bipolar disorder, mirrored those in the United States: a 29% increase for those in counties with the worst air quality. Using this more specific Danish data, the team found early childhood exposures correlated even more strongly with major depression (a 50% increase); with schizophrenia (a 148% increase); and with personality disorders (a 162% increase) over individuals who grew up in areas with the highest quality air.
Researchers have long suspected that genetic and neurochemical factors interact at different levels to affect the onset, severity and progression of these illnesses. So far, scientists have found only modest associations between individual genetic variants and neuropsychiatric disease: for most common polymorphisms, disease risk increase is small, perhaps less than 10%.
This fact led Rzhetsky, who has been studying the genetic roots of a wide variety of neuropsychiatric diseases for over two decades, to look for other molecular factors that might trigger or contribute to the disease mechanism.
Khan, Rzhetsky and the team worked on the project for more than two years, enhancing their models with additional mathematical analyses and data sources.
However, other researchers in the field have noted that this substantial correlation still does not confirm pollution actually triggers the diseases.
While the study did not address the question of how air pollution might trigger neural effects, a large body of experimental studies in animal models suggests that polluting chemicals affect neuroinflammatory pathways and set the stage for later neurodevelopmental problems—many of which occur at the end of childhood as children become adults.
Our results indicate that the physical environment, in particular air quality, warrants further attention in research seeking to elucidate environmental contributors to neurological and psychiatric disease risk. In conclusion, we observed a strong positive association between exposure to environmental pollution and an increase of prevalence in psychiatric disorders in affected patients. Converging data points to neuroinflammatory mechanisms linking environmental compounds to their putative psychiatric consequences. However, these strong associations do not necessarily mean causation; further research will be needed to assess whether air pollution’s neuroinflammatory impacts share common pathways with other stress-induced conditions.—Khan et al.
Khan A, Plana-Ripoll O, Antonsen S, Brandt J, Geels C, Landecker H, et al. (2019) “Environmental pollution is associated with increased risk of psychiatric disorders in the US and Denmark.” PLoS Biol 17(8): e3000353. doi: 10.1371/journal.pbio.3000353