Nitrogen dioxide (NO2) pollutants in the air were associated with increased risk for a Parkinson disease (PD) diagnosis. These findings from a retrospective cohort study were published in JAMA Neurology.

Data from the National Health Insurance Service of South Korea, which covers 97% of the country’s residents, were analyzed for this study. Individuals (N=78,830) who lived in Seoul between 2002 and 2006 were assessed for health status and associated with air quality data collected hourly at 25 sites by Seoul Research Institute of Public Health and Environment.

Participants had a mean age of 54.4 (standard deviation [SD], 10.7) years and 52.1% were women. During up to 9 years of follow-up, incident PD was diagnosed among 338 (0.4%), corresponding with an incident rate of 44.6 per 100,000 person-years (py).

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The PD cohort was significantly older (P <.001) and more likely to be covered by the medical aid program (P <.001). Hypertension (46.7%), diabetes (30.2%), and dyslipidemia (27.5%) were the most common comorbidities.

During the preceding 5 years, median small particulate matter (PM2.5) was 26.5 (range, 18.0-44.4) mg/m3, larger particulate matter (PM10) was 55.5 (range, 41.0-79.0) mg/m3, NO2 was 0.033 (range, 0.026-0.045) ppm, ozone (O3) was 0.019 (range, 0.013-0.025) ppm, sulfur dioxide (SO2) was 0.0053 (range, 0.0036-0.0074) ppm, and carbon monoxide (CO) was 0.59 (range, 0.40-0.82) ppm. During the study period, levels of NO2, SO2, and CO were stable, O3 increased, and PM2.5 and PM10 declined.

In the adjusted model, the highest quantile of NO2 exposure was associated with incident PD (adjusted hazard ratio [aHR], 1.41; 95% CI, 1.01-1.96; P =.045). This association was observed to have a significant 1-year lag (aHR, 1.34; 95% CI, 0.97-1.84; P =.048) but not a 2-year lag (aHR, 1.17; 95% CI, 0.86-1.58; P =.16).

No other pollutants were associated with incident PD.

This study was limited because it assessed only outdoor air pollution and may not reflect indoor air quality and exposure to pollutants.

These data indicated PD risk may be increased with elevated exposure to NO2 over the course of a 5-year period.

The study authors noted that “long-term exposure to air pollution has been…associated with neurodegenerative diseases though systemic inflammation, oxidative stress, and direct invasion into the brain.” They add that because most previous studies on PD and environmental pollutants were done in North America and Europe, “there is a need for investigation in Asian countries, where air pollutant levels are generally higher.”


Jo S, Kim YJ, Park KW, et al. Association of NO2 and other air pollution exposures with the risk of Parkinson disease. JAMA Neurol. Published online May 17, 2021. doi:10.1001/jamaneurol.2021.1335

This article originally appeared on Psychiatry Advisor