Association of NO₂ and Other Air Pollution Exposures With the Risk of Parkinson Disease

Question  Which air pollutant is associated with the development of Parkinson disease (PD)?

Findings  In this cohort study including a nationally representative cohort from a metropolitan city in South Korea (n = 78 830), a statistically significant association was found between exposure to NO₂, especially at high levels, and incidence of PD.

Meaning  These findings suggest that regulation of air pollutants might reduce the incidence of PD.

Importance  The development of Parkinson disease (PD) may be promoted by exposure to air pollution.

Objective  To investigate the potential association between exposure to particulate matters (PM_2.5 and PM₁₀), nitrogen dioxide (NO₂), ozone (O₃), sulfur dioxide (SO₂), and carbon monoxide (CO) and the risk of incident PD.

Design, Setting, and Participants  This retrospective cohort study used data from the Korean National Health Insurance Service. Among the 1 021 208 Korean individuals in the database, those who had lived in Seoul from January 2002 to December 2006 (n = 176 875) were screened for eligibility. A total of 78 830 adults older than 40 years without PD and who lived in Seoul between January 2002 and December 2006 were included in this study. Individuals diagnosed with PD before 2006 (n = 159) and individuals 40 years or younger (n = 97 886) were excluded. Each participant was followed up with annually from January 2007 to December 2015, thereby adding up to 757 704 total person-years of follow-up. Data were analyzed from January to September 2020.

Exposures  Individual exposure levels to PM_2.5, PM₁₀, NO₂, O₃, SO₂, and CO were estimated based on the participants’ residential address at the district level. To evaluate long-term exposure to air pollution, time-varying 5-year mean air pollutant exposure was calculated for each participant.

Main Outcomes and Measures  The outcome measure was the association between air pollution and the risk of incident PD measured as hazard ratios after adjusting for demographic factors, socioeconomic factors, and medical comorbidities.

Results  At baseline, the mean (SD) age of the 78 830 participants was 54.4 (10.7) years, and 41 070 (52.1%) were female. A total of 338 individuals with newly diagnosed PD were identified during the study period. Exposure to NO₂ was associated with an increase in risk of PD (hazard ratio for highest vs lowest quartile, 1.41; 95% CI, 1.02-1.95; P for trend = .045). No statistically significant associations between exposure to PM_2.5, PM₁₀, O₃, SO₂, or CO and PD incidence were found.

Conclusions and Relevance  In this large cohort study, a statistically significant association between NO₂ exposure and PD risk was identified. This finding suggests the role of air pollutants in PD development, advocating for the need to implement a targeted public health policy.