Long-Term Traffic Noise Exposure Linked to Increased Parkinson’s Risk

A comprehensive Danish study involving over 3 million individuals has identified a potential association between long-term exposure to traffic noise near residences and an increased risk of developing Parkinson’s disease. The research also suggests that having a quieter side of a building might mitigate this risk.

Published in the journal JAMA Neurology, the study is among the largest to explore the connection between traffic noise and this neurodegenerative disorder, which primarily affects movement and balance.

The researchers clarified that their findings do not establish a direct causal link between noise and Parkinson’s but indicate that noise pollution could represent a new environmental risk factor warranting consideration alongside genetic and other environmental contributors to the disease.

The Danish Cancer Society team analyzed data from 3.1 million people aged 40 and above, monitored across Denmark between 2000 and 2017. They utilized complete residential address histories dating back to 1990 and applied models to estimate average traffic noise exposure over ten years at both the noisiest and quietest facades of each home.

During the follow-up period, 20,587 individuals were diagnosed with Parkinson’s disease, according to the Danish National Patient Registry.

Results showed that for every 11.5-decibel increase in traffic noise at the loudest side of a residence, the risk of Parkinson’s rose by approximately 3%, after adjusting for factors such as age, sex, education, income, marital status, population density, surrounding green spaces, and exposure to fine and ultrafine particulate air pollution.

When considering the noise difference between the loudest and quietest facades, the association strengthened, with Parkinson’s risk increasing by about 6% for each 11.5-decibel rise at the noisiest side. Additionally, higher noise levels at the quieter facade were linked to a 4% increase in risk per 8.9-decibel increment.

The researchers noted that a noise level difference of 10 decibels or more between the noisy and quiet sides of a home—indicating the presence of a room or area less exposed to street noise—was associated with a reduced Parkinson’s risk among residents in areas where noise exceeded 50 decibels.

This quieter side may allow residents to open windows, sleep, or rest away from traffic noise even when living on busy streets.

Noise exposure in the study was measured using the "Lden" index, which averages traffic noise over 24 hours while giving extra weight to evening and nighttime noise due to its greater potential impact on sleep and rest.

The findings were consistent across genders and various categories of education, income, marital status, and population density. The association remained in a subgroup analysis that included data on smoking and physical activity.

Separately, initial clinical results in humans for an experimental cell therapy for Parkinson’s showed that implanting dopamine-producing nerve cells derived from stem cells into the brain is feasible and preliminarily safe.

The study did not investigate biological mechanisms underlying the observed association, but the researchers suggested that chronic noise exposure might disrupt sleep and activate stress responses in the body, which could contribute over time to neurological or inflammatory processes linked to brain health deterioration.

Parkinson’s disease is a progressive neurological disorder caused by the loss of dopamine-producing nerve cells. Symptoms include tremors, slowed movement, muscle stiffness, and balance problems, along with non-motor symptoms such as sleep and mood disturbances.

The researchers emphasized that as an observational study, their work cannot prove that traffic noise directly causes Parkinson’s disease. Diagnosis relied on hospital and medical records, which might miss early or undiagnosed cases outside hospital settings. There may also be unmeasured factors related to living in noisy areas not fully accounted for in the statistical models.

Nonetheless, the team highlighted the study’s large scale, lengthy follow-up, precise residential history, and adjustment for air pollution exposure as strengths supporting the reliability of the results.

They advocated for urban planning policies aimed at reducing residents’ exposure to road noise, including improving building insulation, regulating traffic flow, locating bedrooms away from streets, and designing homes with quiet facades or courtyards.

They concluded that ensuring a quiet residential side could be a practical approach to lessen potential health effects of noise, even in cities where significantly lowering traffic noise levels is challenging.