A study published in the BMJ looks at residential exposure to traffic noise in Denmark and incidence of dementia.
Dr Rosa Sancho, Head of Research, Alzheimer’s Research UK, said:
“This research, based in Denmark, doesn’t tell us the cause of the increased dementia risk but does add to evidence linking exposure to noise pollution and dementia. 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.
“Previous research has linked air pollution to dementia risk, but in this study, researchers found a separate link between transport noise and dementia. While the researchers estimated people’s exposure to noise levels at residential addresses, we do not know when people in the study were at home or if their homes were fitted with insulation, so further investigation is needed before any firm conclusions can be drawn.
“While eliminating noise pollution may have beneficial effects for our health and wellbeing, we don’t yet know whether it could help to reduce dementia risk. Current evidence suggests that the best way to support brain health is by staying physically and mentally active, eating a healthy balanced diet, not smoking, drinking only within the recommended limits and keeping weight, cholesterol and blood pressure in check.”
Prof Timothy Griffiths, Professor of Cognitive Neurology, Newcastle University, said:
“This is an impressive large epidemiological study that examines the effect of noise exposure on risk of dementia from any cause and exposure to environmental noise over a ten-year period. It is easy to think of possible confounds in a study of this sort in terms of other factors that might be associated with noise exposure. A number of these are considered like measures of socioeconomic status and air pollution: but not exercise which has a large protective effect on dementia risk.
“The work requires further studies to assess reproducibility but if it stands up it begs the question of why the noise exposure is relevant to dementia. The authors suggest neurological and biological effects of stress due to noisy environments as of possible relevance. Another possibility is that noisy environments have a similar effect on the brain to hearing loss: hearing loss has a better-established link to dementia but was not included in this analysis. Both external noise and hearing loss increase the effort required to listen to natural sounds  , which places demands on brain systems implicated in dementia, especially Alzheimer’s disease.
Dr Ivan Koychev, Senior Clinical Researcher, University of Oxford and Clinician Scientist at Dementias Platforms UK (DPUK), said:
“This is a large, good quality study reporting an association between exposure to road and railroad traffic noise and dementia. This result is supportive of previous research linking hearing loss to dementia; this raises the issue of whether the link between noise and dementia is through hearing loss or other mechanisms or indirect reasons. The results of this study are strengthened by the authors controlling for levels of traffic pollution which was recently shown to associate with dementia as well as other diseases (for example, a recent US study found that an initiative to reduce traffic-related pollution resulted in a decrease for newly diagnosed dementia in the area). However it is important to keep in mind that epidemiological studies such as this one can inform about association but rarely about causality. Due to the difficulty in attributing causality in this type of study the suggestion that ‘as many as 1,216 out of the 8,475 cases of dementia registered in Denmark in 2017 could be attributed to these noise exposures’ is controversial.”
‘Residential exposure to transportation noise in Denmark and incidence of dementia: national cohort study’ by Manuella Lech Cantuaria et al. was published in the BMJ at 23:30 UK time Wednesday 8th September.
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Dr Rosa Sancho: “No conflicts to declare.”
Dr Ivan Koychev: “I am an expert committee member of a NICE Technology Assessment committee.”
None others received.