Short-Term Surge in Air Pollution May Trigger Schizophrenia Episodes

Short-term rises in ambient air pollution levels were linked to an elevated risk of schizophrenia hospitalizations, independent of absolute air pollution concentrations, according to a new population-based analysis.¹

This nationwide, time-stratified case-crossover study was conducted on hospitalization records for schizophrenia across 295 administrative divisions of prefecture-level or above cities in China, with records extracted from 2 major health insurance systems from January 2013 to December 2017.

“These findings suggest that additional attention should be paid to the short-term increases in air pollution levels, especially sustained increases during several days, which may be linked to a greater risk of acute schizophrenia episodes,” wrote the investigative team, led by Shaowei Wu, PhD, department of occupational and environmental health, school of public health, Xi’an Jiaotong University Health Science Center.

Ambient air pollution, denoted as the second highest risk factor for noncommunicable diseases, likely serves as a notable risk for mental disorders.² Acute schizophrenia episodes have been linked to acute oxidative stress, a factor that can be stimulated by short-term exposure to ambient air pollution.³

However, existing data are often limited to individual cities or specific subpopulations, without a comprehensive look at all patient populations.⁴ These studies tended to focus on the absolute concentration of ambient air pollution, which could disregard the potential impact of short-term increases in pollution before schizophrenia episode onset.

In this analysis, Wu and colleagues hypothesized air pollution increases between neighboring days (APINs) might be linked to an additional risk of schizophrenia episodes, outside of absolute concentrations, while sustained increases for ≥2 days may be associated with a higher risk of schizophrenia episodes.

The team obtained daily absolute concentrations of fine particulate matter (PM2.5), inhalable particulate matter (PM10), nitrogen dioxide, sulfur dioxide, ozone, and carbon monoxide from a real-time air quality database in China. APINs were generated as the difference in absolute air pollution concentrations on the present day versus the previous day.

An increase in APINs lasting for ≥1 day to ≥4 days was defined by Wu and colleagues for the distribution of different air pollutants: APIN ≥5 µg/m3 for PM2.5 and PM10, APIN ≥1 µg/m3 for nitrogen dioxide and sulfur dioxide, and APIN ≥0.05 mg/m3 for carbon monoxide.

Overall, 817,296 hospitalization records for schizophrenia were extracted from the two databases across 259 Chinese cities. The patient population was 55.04% male and included 30.6% aged 0–39 years, 56.4% aged 40–64 years, and 13.0% aged ≥65 years.

Upon analysis, Wu and colleagues found the 5-day or 6-day moving average APINs demonstrated the strongest associations with schizophrenia hospitalizations. Per-IQR increases in the 6-day moving average APINs of PM2.5, PM10, nitrogen dioxide, sulfur dioxide, and carbon monoxide were respectively associated with increases of 2.37% (95% CI, 0.88–3.88), 2.95% (95% CI, 1.46–4.47), 4.61% (95% CI, 2.93–6.32), 2.16% (95% CI, 0.59–3.76), and 2.02% (95% CI, 0.39–3.68) in schizophrenia hospitalizations.

Notably, these associations remained statistically significant after adjustment for the absolute concentration of each air pollutant. Wu and colleagues indicated these more pronounced associations between schizophrenia hospitalizations and sustained air pollutants could represent the accumulative effect of continuous stress from air pollution.

“It is difficult to directly compare our results with existing studies because no previous studies have investigated the potential adverse effects of short-term and sustained increases in air pollution levels on the risk of acute schizophrenia episodes,” they wrote. “Our findings thus provide novel insights for air pollution-related risk of schizophrenia episodes.”

References

1. _{Bai L, Jiang Y, Wang K, et al. Ambient Air Pollution and Hospitalizations for Schizophrenia in China. JAMA Netw Open. 2024;7(10):e2436915. doi:10.1001/jamanetworkopen.2024.36915}
2. _{Cao, Z., Zhou, J., Li, M. et al. Urbanites’ mental health undermined by air pollution. Nat Sustain 6, 470–478 (2023). https://doi.org/10.1038/s41893-022-01032-1}
3. _{Chien YL, Hwu HG, Hwang TJ, et al. Clinical implications of oxidative stress in schizophrenia: Acute relapse and chronic stable phase. Prog Neuropsychopharmacol Biol Psychiatry. 2020;99:109868. doi:10.1016/j.pnpbp.2020.109868}
4. _{Song R, Liu L, Wei N, et al. Short-term exposure to air pollution is an emerging but neglected risk factor for schizophrenia: A systematic review and meta-analysis. Sci Total Environ. 2023;854:158823. doi:10.1016/j.scitotenv.2022.158823}