Risk of neurologic disorder rises for people who live near traffic noise

Long-term exposure to residential road traffic noise was associated with an increased risk of Parkinson's disease, a study of more than 3 million adults in Denmark showed.

Traffic noise levels at the most exposed facade of people's homes over 10 years was associated with an increased risk of incident Parkinson's disease per interquartile increment of 11.5 dB, after adjusting for sociodemographics, air pollution, and green space (HR 1.03, 95% CI 1.00-1.05), reported Mette Sørensen, PhD, of the Danish Cancer Institute in Copenhagen, and colleagues.

People with a quiet facade had a lower risk of developing Parkinson's disease than those whose homes were exposed to high levels of noise on all sides, the researchers found. A difference of 10 dB or more between the most and least exposed facades was associated with a decline in Parkinson's risk across different levels of traffic noise above 50 dB, they wrote in JAMA Neurology.

Associations were consistent across subgroups defined by sex, education, cohabiting, and population density.

Environmental variables like pesticides, industrial solvents, and air pollution have been tied to Parkinson's risk, as has living in areas with increased potential exposure to toxicants from golf courses.

"These environmental risk factors share a common feature: they are place-based, and they cluster," observed Holly Elser, MD, PhD, of the University of Pennsylvania in Philadelphia, and co-authors in an accompanying editorial.

Noise has emerged as another potential place-based exposure relevant to Parkinson's risk, Elser and colleagues noted. Epidemiological data supporting a causal link between environmental noise and Parkinson's have been scarce, but the biological plausibility of this association is "reinforced by evidence suggesting that excess noise can disrupt circadian rhythms and trigger neuroinflammatory pathways, which are implicated in Parkinson's disease pathogenesis," they wrote.

The Denmark study provides strong evidence that chronic exposure to traffic noise is associated with an increased risk of developing Parkinson's, said Fernando Alonso-Frech, MD, PhD, of the Comprehensive Neuroscience Center in Madrid.

"A particularly interesting finding is that having a facade or area of the home with a noise level more than 10 dB lower than the area most exposed to noise appears to attenuate this association, which reinforces the hypothesis that noise pollution, particularly during periods of nighttime rest, could play a significant role," Alonso-Frech posted on the Science Media Centre website in Spain.

"Although the observed increase in risk is relatively modest at an individual level, the huge proportion of the population exposed to traffic noise means that its potential impact on public health could be considerable," he added.

Sørensen and colleagues assessed 10 years of residential road traffic noise exposure at the most and least exposed facades of the homes of 3.1 million Danish residents who were ages 40 or older at cohort entry.

The researchers cross-linked data from national administrative and health registries with residential addresses and used the Nordic prediction method to estimate road traffic noise levels in 1995, 2000, 2005, 2010, and 2015. The model incorporated traffic variables, road characteristics, and screening effects from buildings, noise barriers, and terrain.

The average baseline age of participants was 51 years, and just over half (51.2%) were women. The mean follow-up time was 13 years, during which 20,587 people were diagnosed with Parkinson's disease.

Study limitations included the use of facade noise rather than indoor noise estimates, Sørensen and colleagues said. The study also lacked data on lifestyle factors.

The analysis focused on road traffic noise in a single high-income country. Results may be different in places where housing, traffic, and medical care vary, the researchers acknowledged.