Traffic Noise a Novel Parkinson’s Risk Factor?

Long-term exposure to residential traffic noise was associated with a higher risk for Parkinson’s disease (PD), independent of air pollution, green space, and socioeconomic factors, a large Danish study showed.However, this association may be mitigated by having a “quiet façade” that provides residents with a reprieve from excessive noise, researchers noted.“From a prevention perspective, ensuring that dwellings provide a quiet side may be important for reducing the potential neurodegenerative effects of chronic noise exposure,” lead investigator Mette Sørensen, PhD, Work, Environment and Cancer, Danish Cancer Institute, Copenhagen, Denmark, and colleagues wrote.The results were published online on July 20 in JAMA Neurology.Environmental Risk for PD?A growing body of research has identified environmental factors such as air quality as potential risk factors for PD. New data add environmental noise to the list. Neuroinflammatory and circadian alterations linked to excessive noise exposure overlap with mechanisms implicated in PD pathogenesis, which researchers said supports the biological plausibility for noise-related dopaminergic neurodegeneration.To study this further, researchers analyzed data on 3,103,577 Danish citizens (mean age, 50.9 years; 51.2% women), who were free of PD at baseline. During a mean follow-up of 13.0 years, 20,587 were diagnosed with PD.Researchers tapped into linked national administrative and health registries and the Danish National Health Survey (DNHS). They obtained information on estimated traffic noise levels at various timepoints and considered key variables such as road type, annual average daily traffic, and travel speed.For each participant, investigators calculated 10-year time-weighted mean exposure to both the most exposed (LDEN-Max) and least exposed (LDEN-Min) facades. The final model controlled for sex, year, education, income, cohabiting, socioeconomic indicators, air pollution, and green space availability.For LDEN-Max, the hazard ratio (HR) in the fully adjusted model was 1.03 (95% CI, 1.00-1.05) per interquartile increment of 11.5 decibels (dB). Adjusting for the difference between noise at the most and least exposed facades strengthened the association (HR, 1.06; 95% CI, 1.02-1.09).Also, having a quiet facade (difference of ≥ 10 dB between most and least exposed facades) was associated with a lower PD risk at LDEN-Max levels above 50 dB.“This pattern suggests that accounting for whether a dwelling has a quiet facade, with a high likelihood of having rooms where residents can retreat from high noise levels captures an additional dimension of noise exposure that is not reflected by LDEN-Max alone,” the authors wrote.More Research NeededThe study found LDEN-Min was associated with an HR of 1.04 (95% CI, 1.02-1.07) per interquartile increment of 8.9 dB.Further adjustments for smoking and physical activity in a DNHS subpopulation resulted in only minor changes in risk. Associations were consistent across subgroups defined by sex, education, cohabiting status, and population density.The study didn’t capture factors such as sound insulation, window type, ventilation, or bedroom location. It also lacked information on noise exposure during commuting and at the workplace, and on lifestyle factors.The study’s data on residential history and validated models for traffic noise estimation “help amplify the case for noise as a novel environmental risk factor of PD,” Dixon Yang, MD, Department of Neurological Sciences, Rush University Medical College, Chicago, and colleagues wrote in an accompanying editorial.An additional subgroup analysis by patient-level characteristics may more fully characterize the traffic-related association between noise and PD, they noted.“Of particular interest are characteristics that have been previously demonstrated to increase or mitigate the risk of PD, including smoking history, diabetes, and hospital contact for traumatic brain injury,” they wrote.“Work that demonstrates the persistence of an association between traffic-related noise and prodromal symptoms that are specific to PD such as anosmia and rapid eye movement sleep behavior disorder would support some specificity of this association and would further represent a key extension of the work,” they added.An analysis that explores whether the association between traffic-related air pollution and incident PD is mediated by sleep disorders may also be helpful.“Given the numerous environmental risk factors of PD that have been identified, there is a need for future work to examine how environmental co-exposures vary in space and time with PD incidence. Moving past these interpretive challenges is the work of the next decade,” the editorialists wrote.The study authors and the editorial writers did not report any conflicts of interest. The DNHS was funded by The Capital Region, Region Zealand, The South Denmark Region, The Central Denmark Region, The North Denmark Region, Ministry of Health and the National Institute of Public Health (University of Southern Denmark).