Key clinical point: Exposure to high concentrations of residential nitrogen dioxide (NO₂) and nitrogen oxides (NO_X) during childhood is associated with a subsequent increased risk of developing schizophrenia.

Major finding: People exposed to mean daily concentrations of >26.5 μg/m³ NO₂ were at an increased risk for schizophrenia vs. those who were exposed to a mean daily concentration of <14.5 μg/m³ (incidence rate ratio, 1.62; 95% confidence interval, 1.41-1.87). Association between exposure to particulate matter PM_2.5 or PM₁₀ and risk for schizophrenia was less consistent than that for NO₂ or NO_X.

Study details: Danish population-based study included 230,844 individuals born during 1980-1984;

2,189 individuals were diagnosed with schizophrenia during follow-up.

Disclosure: The study was funded by the Lundbeck Foundation, the Stanley Medical Research Institute, the European Research Council, NordForsk, the Novo Nordisk Foundation, the National Health and Medical Research Council, the Danish National Research Foundation. The authors declared no conflicts of interest.

Commentary

“While urbanicity is a well-established risk factor for schizophrenia, mechanistic underpinnings of this observation are not clear and could potentially involve factors such as infection, selective migration patterns, or pollution. Air pollution can impact the brain through multiple pathways including chronic inflammation and oxidative stress, possibly contributing to neurodevelopmental disorders such as schizophrenia. This rigorous and methodologically sophisticated study adds to the literature indicating that exposure to environmental pollution is linked with an increased risk of schizophrenia. While contributors to the development of schizophrenia are multiple and varied, reducing ambient air pollution could have the effect of preventing some schizophrenia cases, especially in more polluted and densely population regions.”

Martha Sajatovic, MD

Professor of Psychiatry and of Neurology

Willard Brown Chair in Neurological Outcomes Research

Director, Neurological and Behavioral Outcomes Center, University Hospitals Cleveland Medical Center

Case Western Reserve University School of Medicine