Noise caused by cars and trains has been linked to an increased risk of dementia, a new study has found.
Almost two million adults aged 60 or older living in Denmark were monitored by researchers between 2004 and 2017.
The research, published in the BMJ, found that over an average of 8.5 years some 31,219 people received a diagnosis of Alzheimer’s disease, 8,664 a diagnosis of vascular dementia, and 2,192 were deemed to have Parkinson’s disease-related dementia.
Experts concluded that more than 1,000 cases of dementia in participants could be attributed to the road and rail noise audible from their homes.
Teams estimated the amount of noise people heard based on their proximity to the most and least exposed facades of buildings.
Using hazard ratios and the percentage of exposed people in each noise category, they calculated the population-attributable risk for road traffic and railway noise to draw their conclusions.
They said of the 8,475 new cases of dementia registered in the country in 2017 “the diagnosis in an estimated 963 patients was attributed to road traffic noise and in 253 patients to railway noise”.
In the study, they wrote: “In this large nationwide cohort study, we found transportation noise from road traffic and railway to be associated with an increased risk of all cause dementia and dementia subtypes, especially Alzheimer’s disease.
“If these findings are confirmed in future studies, they might have a large effect on the estimation of the burden of disease and healthcare costs attributed to transportation noise.
“Expanding our knowledge on the harmful effects of noise on health is essential for setting priorities and implementing effective policies and public health strategies focused on the prevention and control of diseases, including dementia.”
Teams acknowledged that their work did not take into account a lot of lifestyle factors which are recognised risks of dementia.
However, they said their models did include several socioeconomic variables associated with lifestyle.
Dementia causes memory loss, difficulty concentrating and confusion in sufferers.
Dr Ivan Koychev, senior clinical researcher at the University of Oxford and clinician scientist at Dementias Platforms UK (DPUK), called it “a large, good quality study”.
But he cautioned against jumping to conclusions and said there is a difficulty in attributing the cause of a disease in this type of study.
He said the suggestion that more than 1,000 of the dementia cases registered in Denmark in 2017 could be attributed to noise exposures was “controversial”.
Dr Rosa Sancho, head of research at Alzheimer’s Research UK, said the findings “add to evidence linking exposure to noise pollution and dementia”.
She added: “While this is a large observational study using detailed estimates of residential noise levels, it only considers road and rail noise and doesn’t evaluate established lifestyle risk factors for dementia, which could have also attributed to the increased risk of dementia.”
Professor Timothy Griffiths, professor of cognitive neurology at Newcastle University, said the research “requires further studies to assess reproducibility but if it stands up it begs the question of why the noise exposure is relevant to dementia.”