Nitrogen Dioxide Exposure Linked With Risk of Parkinson Disease

Residing in areas with busy roads or highways that are prone to greater exposure of nitrogen dioxide (NO₂) may increase risk of Parkinson disease (PD), according to study findings published in JAMA Neurology.

Researchers highlight that air pollution exposure, a significant public health hazard, affects more than 80% of urban area residents at levels exceeding that set by the World Health Organization.

Associated with several adverse events, including migraine prevalence and severity, and increased risk of death from respiratory disease, researchers say that long-term air pollution exposure has been identified to be associated with neurodegenerative diseases through systemic inflammation, oxidative stress, and direct invasion into the brain.

Moreover, they note that exposures to environmental pollutants, such as pesticides, metals, and air pollution, have been suggested as risk factors for PD.

Seeking to further assess this potential link, particularly which air pollutants may increase risk of PD development, researchers examined retrospective data from the Korean National Health Insurance Service for individual exposure levels to particulate matters (PM_2.5 and PM₁₀), NO₂, ozone (O₃), sulfur dioxide (SO₂), and carbon monoxide (CO).

“Since most studies were conducted in North American and European countries, there is a need for investigation in Asian countries, where air pollutant levels are generally higher than those in other countries,” noted researchers.

The study included 78,830 adults older than 40 years without PD (mean [SD] age, 54.4 [10.7] years; 52.1% female) who lived in Seoul, South Korea, between January 2002 and December 2006, and met inclusion criteria. The study cohort participated in annual follow-ups from January 2007 to December 2015, amounting to 757,704 total person-years of follow-up.

Each participant’s exposure level to the air pollutants was estimated by residential address at the district level, in which a time-varying 5-year mean air pollutant exposure was calculated to evaluate long-term impact.

Among the study cohort, 338 participants were newly diagnosed with PD in the 9 years of follow-up, in which those who developed incident PD were significantly older (mean [SD] age, 54.4 [10.7] years vs 66.5 [9.7] years; P < .001) and were more likely to be receiving Medicaid (2.8% [2208 of 78,830] vs 7.1% [24 of 338]; P < .001).

In assessing the air pollutants, NO₂ was the sole pollutant whose exposure was associated with risk of incident PD (HR for highest vs lowest quartile, 1.41; 95% CI, 1.02-1.95; P = .045 for trend), which remained robust after adjusting for confounders, such as age, sex, and insurance type.

“This finding suggests the role of air pollutants in PD development, advocating for the need to implement a targeted public health policy,” said the study authors. “To account for the long prodromal stage of PD, the effect of air pollutants according to various exposure duration and lag analysis should be investigated.”

Reference

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