Road Traffic Noise, Noise Difference Between Residential Facades, and Risk of Parkinson Disease

Importance: Transportation noise has been proposed as a risk factor for Parkinson disease (PD), but epidemiological evidence remains limited and inconsistent. Objective: To investigate whether long-term residential exposure to road traffic noise is associated with a higher risk of PD. Design, Setting, and Participants: This was a Danish nationwide prospective cohort study with follow-up from 2000 to 2017. Danish residents 40 years and older were eligible. Analyses were conducted from April to May 2026. Exposures: Based on complete residential address history from 1990 onward, 10-year time-weighted residential exposure to road traffic noise (LDEN) at the most and least exposed facades were assessed for all participants. Main Outcome and Measures: Incident PD cases during follow-up were identified in the National Patient Register. Analyses were conducted using Cox proportional hazards models. Results: Of 3 542 488 eligible individuals, 438 911 were excluded (prevalent PD, incomplete address history, or missing covariates), leaving 3 103 577 participants (mean [SD] baseline age, 50.9 [11.7] years, 1 588 658 female [51.2%]). Among 3 103 577 participants, 20 587 developed PD during follow-up. Road traffic noise at the most exposed facade (LDEN-Max) was associated with a hazard ratio (HR) of 1.03 (95% CI, 1.00-1.05) per interquartile increment of 11.5 dB in models adjusted for individual- and area-level sociodemographics, air pollution (fine particulate matter with a diameter of 2.5 µm or less [PM2.5] and ultrafine particles), and green space covariates. Having a difference between noise at the most and least exposed facades (Δnoise, indicator of having a quiet side) of 10 dB or more was associated with a decline in PD risk across different levels of LDEN-Max above 50 dB. Also, accounting for Δnoise strengthened the association between LDEN-Max and PD (HR, 1.06; 95% CI, 1.02-1.09). Noise at the least exposed facade was associated with PD, with an HR of 1.04 (95% CI, 1.02-1.07) per interquartile increment of 8.9 dB. Associations were consistent across strata of sex, education, income, cohabiting status, and population density and after additional adjustment for smoking and physical activity in a subpopulation. Conclusions and Relevance: Results of this cohort study show that long-term exposure to road traffic noise was associated with higher PD risk. Having a quiet facade mitigated this association. These findings suggest noise as a novel risk factor for PD and support mitigation strategies ensuring a quiet residential side.