Medical research has long confirmed that traffic noise is not just a daily nuisance, but a real threat to public health.
Prolonged exposure to the sounds of cars and trucks on busy streets is not only annoying, but may also be associated with an increased risk of heart disease, high blood pressure, sleep disorders and psychological problems, and may negatively affect the mental development of children.
In a recent Danish study, researchers attempted to answer an important question: Does living near noisy roads increase the long-term risk of developing neurodegenerative diseases, such as Parkinson's disease?
To answer this question, the research team followed more than 3 million Danes over the age of 40 for nearly 20 years. After analyzing the data, the researchers found that prolonged exposure to traffic noise inside homes is associated with an increased risk of Parkinson's disease. This association was clearly evident on both sides of the house—the side facing the street, which was more exposed to noise, and the quieter back side.
The higher the noise level in the home, the greater the risk of developing the illness. However, having a quieter side of the house, at least 10 decibels quieter than the side facing the street, helped reduce this risk for residents of noisy areas.
The study, published in JAMA Neurology, recorded 20,587 participants who developed Parkinson's disease during the follow-up period.
As the average age of the population rises around the world, rates of Parkinson's disease are increasing. It is currently the second most common neurodegenerative disorder, affecting more than 8.5 million people.
The disease results from a complex interaction between genetic and environmental factors, and its essence lies in the loss of nerve cells responsible for producing dopamine in the brain, which affects movement, memory, and the ability to speak.
While factors like genetics and age cannot be changed, scientists are working to identify modifiable risk factors—those that can be controlled to reduce the likelihood of developing the disease. After air pollution was identified as one such factor, attention has recently turned to traffic noise, as noise can disrupt sleep and trigger stress and inflammatory responses in the body, processes believed to contribute to brain cell damage associated with Parkinson's disease.
For the study, the researchers relied on detailed health records and residential addresses in Denmark, which are among the most accurate in the world. Instead of using questionnaires asking people to estimate noise levels around their homes, the team used a scientific model to calculate actual noise levels in each home since 1990.
The researchers measured the noise level on the noisiest side of the house (usually facing the street) and the quietest side (facing the backyard or inner courtyard), then calculated the average noise exposure for each person over ten years, taking into account individuals moving between different addresses during that period.
To identify those with Parkinson's disease, the team used the Danish National Patient Registry to track cases diagnosed over 18 years. They also controlled for other factors that could influence the results, such as age, gender, income level, and air pollution, to make the relationship between noise and the disease clearer and more precise.
The data showed that prolonged exposure to traffic noise is associated with an increased risk of Parkinson's disease. Every 11.5 decibel increase in noise levels on the street-facing side was associated with a 3% increased risk. On the quieter side, where bedrooms are often located, the association was even stronger, with every 8.9 decibel increase associated with a 4% increased risk.
The researchers also found that having a quiet side of the house at least 10 decibels away from the noisy side helped reduce the risk of injury for residents of areas where noise levels exceed 50 decibels.
These findings suggest that traffic noise in residential areas is not merely a comfort issue, but may be a novel environmental risk factor for Parkinson's disease. With the number of people affected globally increasing, reducing exposure to preventable environmental factors is becoming increasingly important for millions.
These findings may help city planners design quieter neighborhoods, such as placing bedrooms and living rooms in areas away from busy roads, which could help reduce the growing burden of this disease on communities and health systems.
