Association of nitrogen dioxide and other air pollution exposures with the risk of Parkinson disease

1. Among a cohort of individuals from South Korea, exposure to nitrogen dioxide (NO₂) was found to be associated with an increased risk of developing Parkinson’s disease (PD).

Evidence Rating Level: 2 (Good)

Increased air pollution levels have been identified to be associated with neurodegenerative changes in recent studies. This retrospective cohort study aimed to determine the association between incidence of PD and six types of air pollutants (nitrogen dioxide [NO₂], sulfur dioxide [SO₂], carbon monoxide [CO], and particulate matters [PM_2.5 and PM₁₀]). It enrolled 78 830 adults older than 40 years (mean age [SD] = 54.4 [10.7], 52.1% were female) without PD from different districts. The study collected data on air pollutant levels from the different districts in which the participants resided. Each participant was followed up with annually for 9 years to determine if a new diagnosis of PD had been made. The study also collected data on other covariates such as age, sex, pre-existing comorbidities, and type of health insurance. The study found that exposure to NO₂ was associated with an increase in risk of PD (hazard ratio for highest vs. lowest quartile, 1.34; 95% CI, 1.02 – 1.95, p = 0.045). The association was present after adjusting for demographic factors and comorbidities. In comparison, there was no association found between levels of SO₂, CO, PM_2.5, PM₁₀ and incidence of PD, for both adjusted and non-adjusted analysis. The study demonstrated that the hazard ratios for incident PD according to NO₂ exposure showed a statistically significant increase when NO₂ levels were greater than 0.038 parts per million. One of the studies largest limitation was not adjusting for factors such as socioeconomic status, occupation, and workplace exposures. However, this is still one of few large-scale studies evaluating the link between air pollutants and incident PD. Given the study’s findings, future studies in this area are encouraged and required to make further informed public health policies.

Click to read the study in JAMA Neurology

Image: PD

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