According to the largest study, dementia risk is increased by exposure to noise from railways and road traffic.
Although research has linked transport noise to various health conditions, including heart disease, diabetes, and obesity, studies on noise from transport and dementia have been inconsistent and limited.
A study of two million adults over a period of ten years has shown that those who live in areas where there is a lot of noise from transport vehicles are at greater risk for developing dementia, particularly Alzheimer's disease. These findings were published by the BMJ.
Two million people aged 60+ who lived in Denmark between 2004-2017 were asked by researchers to determine if long-term exposure to railway noise and road traffic could increase the likelihood of developing dementia. For every residence in the country, the exposure levels at the most and least exposed sides of buildings were estimated.
The study looked at the potential influence factors of residents and their neighborhoods. It concluded that transport noise could account for as high as 1,216 of the 8,475 dementia cases in Denmark in 2017.
An estimated 963 of those cases were due to noise from road traffic, while 253 patients were caused by noise from railways.
The researchers found that all-cause dementia, and subtypes thereof, were associated with increased noise levels from railways and road traffic in a large, nationwide cohort study.
They found a general pattern in which higher noise exposure is associated with greater risk. They said that if these findings are confirmed by future studies, it could have a significant impact on the estimation of healthcare costs and the burden of disease attributed to noise pollution from transportation vehicles.
Dementia is a major health problem in the world. The number of people with dementia is expected to rise to 130 million globally by 2050. Experts are increasingly confirming that environmental factors play a part in the development and progression of dementia.
While previous research has shown that air pollution is linked to dementia risk in the elderly, this study found a distinct connection between noise from transport and dementia.
According to the researchers, it was possible to reduce the dementia burden by combating traffic noise. They stated that it is crucial to increase our knowledge about the detrimental effects of noise on health in order to set priorities and implement effective policies and public health strategies aimed at the prevention and control and management of diseases such as dementia.
Noise may be linked to dementia by triggering the release of stress hormones, sleep disturbance, and immune system changes.
Although the study was observational, it did not prove cause. It also had limitations such as a dearth of information about sound insulation in homes, which could affect noise exposure. Its strengths were its large sample size, long follow up time, and high quality assessment of noise exposure.
The investigation was described by Dr Ivan Koychev (a senior clinical researcher at Oxford and a dementia expert), as a high-quality study.
He said that the results were strengthened by the fact that traffic pollution levels, which has been associated with dementia and other diseases, was controlled for.
Professor Timothy Griffiths of cognitive neurology at Newcastle University also didn't participate in the research. He said that it was an impressive epidemiological study which raises the question about the relevance of noise exposure to dementia.
In a BMJ-linked editorial, US researchers stated that the widespread exposure to noise and the limited tools available for people to protect themselves from it support the World Health Organizations argument.
They stated that reducing noise from transportation, land use or building codes should be a priority for public health.
Dr Rosa Sancho is the head of research for Alzheimers Research UK. She stated that the best way to keep brain health was to be physically and mentally active, to eat a balanced diet, and to control your weight, cholesterol, and blood pressure.