Dementia, Alzheimer’s: Traffic noise increases the risk

Modifiable risk factors for dementia are receiving increasing attention. Researchers have linked noise pollution to several health problems.
A Danish study shows a possible link between transport noise and an increased risk of various forms of dementia, including Alzheimer’s disease.
More than 55 million people worldwide have some form of dementia, according to the World Health Organization (WHO). With the world’s population aging, experts expect that number to exceed 150 million by 2050.

Modifiable risk factors for dementia

Identifying potentially modifiable risk factors for dementia is key to preventing and managing this growing global health crisis.
A new Danish study in the journal The BMJ suggests that exposure to traffic noise increases the risk of developing all-cause dementia, particularly Alzheimer’s disease. Numerous studies have established a consistent link between noise pollution and various health problems such as obesity, diabetes and coronary heart disease. However, research on the effects of noise on dementia is scarce.

Recognizing the need for more controlled testing, the researchers investigated the potential association between long-term residential exposure to transport noise and dementia risk. Transport noise is the second environmental risk factor for public health in Europe, after air pollution. Around 20% of the European population is exposed to transport noise above the recommended level of 55 decibels.

Effects of disturbed sleep

Exposure to this level of noise at night is of particular concern, as sleep is a critical period for mental and cognitive restoration.
Experimental studies suggest that fragmented sleep resulting from sound disturbances is associated with increased oxidative stress, alterations in the immune system, and increased systemic inflammation. Experts consider all of these conditions to be early events in the onset of dementia and Alzheimer’s disease.

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The new study looked at almost 2 million adults, aged 60 or over, who lived in Denmark between 2004 and 2017. The researchers estimated exposure to road traffic and rail noise for all residential addresses in the participants and focused on the most and least exposed sides of the buildings.

The team used Denmark’s high-quality national health registries to identify cases of all-cause dementia and other types of dementia reported over an 8.5-year period. These pathologies included Alzheimer’s disease, vascular dementia and Parkinson’s disease. More than 103,000 new cases of dementia appeared during this period. Further analysis of the study data revealed that noise from road traffic and railways was associated with a higher risk of all forms of dementia, including Alzheimer’s disease. Several animal studies indicate that continuous noise exposure activates the formation of key genes that can lead to neuropathological changes related to Alzheimer’s disease in the hippocampus of mice.

Reduce the negative effects of noise

The authors of the study also note a stabilization or a decrease in the risk ratios on the most exposed sides of the buildings. These seemingly contradictory data are potentially the result of investments in better sound insulation at higher noise levels. The apparent priority given to noise reduction measures may explain other study findings that suggest a higher risk of dementia for people living in suburban areas than for those living in urban areas.

Although large and comprehensive, this study was observational. For this reason, it is not possible to establish causality.
Other limitations of the study include the lack of information about lifestyle habits, which may play a key role in a person’s risk of dementia. In addition, the authors of the study did not take into account noise from airports, noise from industrial activities or noise exposure in the workplace. The researchers conclude by noting that future studies are needed to expand global knowledge of the adverse health effects and health costs attributed to noise pollution.

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While some factors cannot be controlled at the individual level, they can certainly be addressed at the population level through noise pollution policies. »
In a linked editorial US researchers agree on the need to make noise reduction a public health priority. They state: “The widespread and substantial noise exposures worldwide, the severity of the associated health consequences, and the few tools people have to protect themselves strongly support the WHO argument that ‘noise pollution is not only an environmental nuisance, but also a threat to public health. Reducing noise through transportation and land use programs or building codes should become a public health priority. »


Residential exposure to transport noise in Denmark and incidence of dementia: a national cohort study.

Environmental Burden of Disease (EGB)


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