TOPLINE:

Long-term exposure to air pollutants, particularly fine particulate matter with diameter 2.5 μm (PM_2.5), nitrogen dioxide (NO₂), and black carbon (BC), was associated with a higher risk of developing Parkinson's disease (PD).

METHODOLOGY:

• Researchers conducted a nationwide administrative cohort study to determine whether long‑term exposure to air pollutants is associated with the incidence of PD in Denmark.
• They evaluated 3,280,190 Danish residents who were aged 30 years or older at baseline (mean age, 53.2 years; 51.6% women) between 2000 and 2018.
• The incidence of PD was defined as either the first hospital contact for primary PD or the first redeemed prescription of PD-specific medication, as recorded in the national patient registry and prescription registry, respectively.
• Annual average air pollutant — PM_2.5, NO₂, BC, and ozone during the warm season (O₃w) — exposure concentrations were evaluated at participant residential addresses at baseline.

TAKEAWAY:

• During a mean follow-up period of 15.7 years, 36,665 residents developed PD. Annual mean concentrations of PM_2.5, NO₂, BC, and O₃w were 12.4 μg/m³, 20.2 μg/m³, 1.01 × 10^-5/m, and 80.2 μg/m³, respectively.
• Each interquartile range increase in PM_2.5, BC, and NO₂ concentrations was associated with a 5%, 4%, and 3% higher risk of developing PD, respectively; however, no significant association was observed for O₃w.
• The association between PM_2.5 and the risk for PD was stronger among women and unemployed individuals, and associations of NO₂ and BC with the risk for PD were stronger among older individuals (aged 58.4 years or older) and those in the highest household income quintile.

IN PRACTICE:

"This large study provides robust new evidence in support of air pollution as a risk factor for PD," the authors wrote.

SOURCE:

This study was led by Thomas Cole-Hunter, PhD, Section of Environmental Health, University of Copenhagen, Copenhagen, Denmark. It was published online on March 02, 2026, in Movement Disorders.

LIMITATIONS:

This study relied on spatial exposure models for 2010, assuming that participants did not change address during follow‑up, but approximately one third of participants moved, potentially leading to exposure misclassification. This study lacked data on smoking, BMI, and occupation; hence, residual confounding cannot be ruled out. Additionally, the diagnosis of PD was based on registry data, which may have led to misclassification of the disease, especially for prescription-based definitions.

DISCLOSURES:

This study received support from the Health Effects Institute Research Agreement, which was jointly funded by the US Environmental Protection Agency and certain motor vehicle and engine manufacturers, and the Novo Nordisk Foundation Challenge Programme. The authors declared having no relevant conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.