Long-term traffic noise exposure may raise Parkinson’s risk, while having a quieter side of the home could offer some protection, research suggests.
Ongoing road noise was linked to a higher likelihood of developing the neurodegenerative condition.
The findings suggest sleep disruption and stress throughout the body may help explain the link, although the study does not prove that noise causes the disease.
Researchers in Denmark analysed more than three million people aged 40 and over between 2000 and 2017.
None of the participants had Parkinson’s disease when the study began.
For every increase of about 11 decibels on the side of a home most exposed to traffic, the risk of developing the condition rose by around three per cent.
A decibel is a unit used to measure sound intensity.
On the side of the home least exposed to traffic, the risk rose by four per cent for every additional nine decibels of noise.
However, having one side of the home that was at least 10 decibels quieter than the other appeared to offer some protection, particularly for people exposed to higher overall noise levels.
The authors said people without a quiet side may face more persistent and unavoidable noise, particularly at night, when it may be more harmful.
They said previous studies that examined only the loudest side of a home may have underestimated the health risks by failing to consider whether residents had a quieter place to retreat to.
The results remained consistent regardless of sex, education, income, cohabiting status and local population density.
The researchers suggested that persistent noise could contribute to the condition by disrupting sleep, which is important for brain health, and triggering the body’s stress response.
Noise may also cause neuroinflammation, which is inflammation affecting the brain and nervous system, and oxidative stress in areas linked to dopamine production.
Oxidative stress is a form of cell damage caused by unstable molecules, while dopamine is a chemical involved in controlling movement.
Parkinson’s disease is the second most common neurodegenerative disorder worldwide, affecting more than 11m people.
That number is expected to more than double in the coming decades as people live longer and populations grow in some countries.
Parkinson’s disease develops as nerve cells in the brain gradually become damaged or die. Many symptoms are caused by the loss of dopamine-producing cells, resulting in irregular brain activity.
The exact cause remains unknown, and there is currently no cure.
“Therefore, identifying potentially modifiable environmental factors is a public health priority,” said Fernando Alonso Frech, neurologist and researcher at the HM CINAC Comprehensive Neuroscience Center, who was not involved in the study.
Frech said the large proportion of people exposed to road traffic noise meant its potential effect on public health could be considerable.
“In this context, the findings reinforce the importance of policies aimed at reducing urban noise pollution, through strategies such as urban planning, the creation of noise barriers, reducing traffic in residential areas, or designing housing with façades and resting spaces that are less exposed to noise.”
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