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Train and Traffic Noise May Raise Alzheimer’s Risk

September 22, 2021

Living near a noisy road or train route may increase the risk of developing Alzheimer’s disease or other forms of dementia. Those are the findings of a new analysis that looked at nearly 2 million older adults living in Denmark between 2004 and 2017.

The study, from researchers at the University of Southern Denmark and other institutions, used data from the Danish Health Registry, which uses hospital, doctor and drug prescription records to track the health of all citizens living in the country. Among 1 ,938,994 adults 60 and older, the researchers identified 103,500 who had some form of dementia. Most had Alzheimer’s disease.

They tracked their exposure to traffic and railway noise over a typical 10-year period, based on whether their homes faced busy roads and train tracks. They considered such factors as typical noise levels during the day, evening and night; how close their homes were to roads and train tracks; what kinds of vehicles (for example, trucks or cars) used those roads; and what floor they lived on.

The researchers found that exposure to the highest noise levels was associated with an increased risk of developing dementia, especially Alzheimer’s disease. In general, the higher the noise levels, the greater the risk.

Air pollution has also been tied to an increased risk of Alzheimer’s, and busy roads would be expected to have high levels of soot and other air pollutants. But the researchers considered pollution levels, and found that traffic noise was independently associated with an increased Alzheimer’s risk. They also considered socioeconomic, lifestyle and other demographic features. Still, the link between noise and Alzheimer’s risk held.

Other studies have linked so-called “noise pollution” to heart disease, diabetes and obesity. But this is the largest analysis to date to link noise levels of Alzheimer’s risk. The findings were published in the British medical journal BMJ.

The study observed only a link between noise and Alzheimer’s and cannot prove cause and effect. But the researchers suggested several reasons for why high noise levels may be tied to a higher Alzheimer’s risk. A noisy environment, particularly at night, may disrupt sleep, and poor sleep has been linked to an increased risk of Alzheimer’s disease. Noise may also raise stress levels, including levels of the stress hormone cortisol, and stress has been tied to a higher risk of dementia. In animal studies, exposure to loud noise can change the structure of parts of the brain critical for memory.

In an editorial accompany the study, researchers point out that other forms of noise, such as airports and industrial on-the-job noise, could also impact brain health. “The widespread and substantial exposures to noise worldwide, the severity of associated health consequences, and the limited tools available for people to protect themselves, strongly support the World Health Organization’s argument that ‘noise pollution is not only an environmental nuisance but also a threat to public health,’” they write. “Reducing noise through transportation and land use programs or building codes should become a public health priority.”

By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.

Source: Manuella Lech Cantuaria, Frans Boch Waldorff, Lene Wermuth, et al: “Residential exposure to transportation noise in Denmark and incidence of dementia: national cohort study.” BMJ, Sept. 9, 2021

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