Living in a noisy neighbourhood? Long-term exposure to road traffic noise may do more than disturb your sleep. It could increase the risk of Parkinson's disease—one of the world's fastest-growing neurological disorders—according to a large Danish study published in JAMA Neurology.
The findings assume particular significance for India, where rapid urbanisation, increasing vehicular traffic and rising life expectancy are expected to substantially increase the burden of Parkinson's disease over the coming decades.
The nationwide cohort study titled "Road Traffic Noise, Noise Difference Between Residential Facades, and Risk of Parkinson's Disease" followed more than 3.1 million adults in Denmark over nearly two decades and found that people exposed to higher levels of road traffic noise over a prolonged period were more likely to develop Parkinson's disease.
The researchers also reported that people whose homes had a relatively quieter side or "quiet facade" appeared to have a lower risk despite living in noisy neighbourhoods.
The study tracked 3,103,577 adults aged 40 years and above between 2000 and 2017, during which 20,587 participants developed Parkinson's disease. Using residential address histories dating back to 1990, researchers estimated each participant's exposure to road traffic noise over a 10-year period while accounting for air pollution, socioeconomic factors and surrounding green spaces.
After adjusting for these variables, long-term exposure to higher road traffic noise remained associated with an increased risk of Parkinson's disease.
"Our findings suggest that road traffic noise may represent a novel environmental risk factor for Parkinson's disease," the authors wrote. "Importantly, having access to a quieter residential facade appeared to attenuate the association, supporting urban planning strategies that incorporate quiet living environments."
The researchers found that the protective effect became apparent when there was at least a 10-decibel difference between the noisiest and quietest sides of a residence.
Although the increase in individual risk was modest, neurologists say the implications for densely populated countries such as India could be considerable because millions of people are chronically exposed to excessive traffic noise.
India is already witnessing a steady rise in Parkinson's disease, driven largely by an ageing population. The condition, characterised by progressive loss of dopamine-producing brain cells, causes tremors, stiffness, slowness of movement, balance problems and, in many patients, cognitive decline.
While advancing age remains the strongest risk factor, increasing evidence suggests that environmental exposures—including pesticides, air pollution and now possibly chronic noise—may influence disease development.
The study is among the largest to examine the relationship between transportation noise and Parkinson's disease and is one of the first to evaluate whether residential design can modify that risk.
According to the researchers, chronic noise exposure may trigger repeated activation of the body's stress response, disturb sleep and promote systemic inflammation—all biological mechanisms that have been implicated in neurodegenerative diseases.
"Our results support the hypothesis that prolonged exposure to environmental noise may contribute to neurodegeneration through chronic stress pathways and sleep disruption," the authors noted.
The findings also reinforce the importance of urban planning measures that reduce residents' long-term exposure to traffic noise.
According to the Central Pollution Control Board (CPCB), noise levels in many metropolitan cities frequently exceed prescribed limits, particularly along busy roads and commercial areas. Constant exposure to traffic noise has already been linked to hypertension, cardiovascular disease, sleep disorders and mental stress. The new evidence suggests that neurological health may also need to be considered while framing urban environmental policies.
Neurologists caution that the study does not establish a direct cause-and-effect relationship. Being observational in nature, it demonstrates an association rather than proving that traffic noise causes Parkinson's disease. Nevertheless, its large sample size, long follow-up period, and adjustment for major confounding factors make the findings difficult to ignore.
"These findings suggest that reducing traffic noise and ensuring access to quieter residential environments may contribute not only to better cardiovascular and mental health but also potentially reduce the long-term risk of neurodegenerative diseases such as Parkinson's," the researchers concluded.
