In the ‘largest study of its kind’, a group of Danish researchers has observed that transportation noise from road traffic and railways is associated with ‘an increased risk of all-cause dementia and dementia subtypes, especially Alzheimer’s disease’.
Until recently, research into the link between transport noise and dementia was scarce, small-scale and produced inconsistent findings.
This latest nationwide cohort study, however, measured the long-term residential exposures of around 2 million adults, aged over 60, who lived in Denmark between 2004 and 2017. They did this by calculating time-weighted 10-year running means for the least and most exposed facades of the participants’ home addresses.
The average follow-up period was 8.5 years, during which 103,500 developed dementia. Of those, 31,219 were diagnosed with Alzheimer’s disease, 8,664 with vascular dementia and 2,192 with Parkinson’s disease.
Adjustments were made for covariates in multiple models, including various sociodemographic and socioeconomic variables, as well as air pollution [particulate matter (PM2.5) and nitrogen oxide (NO2)] – an established risk factor for dementia.
An article published in the British Medical Journal, in September, conveyed the researchers’ discovery of a general pattern of higher hazard ratios with increasing noise exposure.
Based on these ratios and the percentage of exposed participants in each noise category, it was evaluated that, of the 8,475 all-cause dementia cases registered in 2017, as many as 1,216 were attributable to transport noise (963 due to road-traffic noise and 253 due to railway noise).
High level exposure to road traffic and railway noise were jointly associated with elevated risk of all-cause dementia and Alzheimer’s disease. Indeed, when compared to people living in areas with <40 dB exposure, those exposed to road traffic noise ≥55 dB and railway noise ≥50 dB were 27% and 24% more likely to develop Alzheimer’s disease, respectively. Only road traffic noise was associated with a raised risk of vascular dementia, while indication of an association between Parkinson’s disease-related dementia and transportation noise could not be confidently identified, owing to ‘few participants’ with the condition.
As a purely observational study, it could not confirm that noise exposure causes dementia, but does add to existing evidence of a relationship (we explored the possible nexus in edition 333 of BC Disease News (here)], as elucidated by Lead Author, Dr. Manuella Cantuaria:
‘Epidemiological studies have consistently linked transportation noise to various diseases and health conditions, such as coronary heart disease, obesity, and diabetes [read our article in edition 334 (here)]. The proposed biological mechanisms for an effect of noise on health are noise induced stress reactions, with activation of the autonomic nervous and the endocrine system and subsequent release of stress hormones, affecting several physiological functions. Exposure to noise during the night can also lead to sleep disturbance and fragmented sleep. Experimental studies have found associations between transportation noise at night time and endothelial dysfunction, increased oxidative stress, alterations in the immune system, and increased systemic inflammation, which in turn are regarded as early events in the onset of dementia and Alzheimer’s disease’.
Acknowledged limitations of the research include a lack of information on prevalence of sound insulation in homes, on time spent at home, on aircraft noise exposure and on occupational and lifestyle risk factors for dementia.
However, Head of Research at Alzheimer’s Research UK, Dr Rosa Sancho, signalled that ‘further investigation’ could produce a corroboration of results and allow ‘firm conclusions’ to be drawn.
Having been dubbed an ‘impressive’ and ‘good-quality’ study by several senior academics in the UK, it is unsurprising that newspaper headlines have called for transportation noise to be treated as a ‘public health priority’.
Transportation noise has been ranked 2nd in a list of the worst environmental risk factors for public health in Europe, with more than 18% of the UK’s urban population thought to be exposed to harmful noise levels (14.5% by road traffic alone).
We are therefore greatly interested in the findings to emerge from the present study, not least because it calls into question whether occupational deafness claimants may be eligible for more significant damages, in respect of latent noise-induced neurodegenerative disease.
Speaking with The Independent, University California Los Angeles (UCLA) Epidemiologist, Professor Beate Ritz, theorised that exposure to noise at work ‘might influence vulnerability to exposures to ambient noise in later life’.
 Andrew Gregory, ‘Transport noise linked to increased risk of dementia, study finds’ (9 September 2021 The Guardian) <https://www.theguardian.com/society/2021/sep/09/transport-noise-linked-to-increased-risk-of-dementia-study-finds> accessed 7 October 2021.
 Cantuaria ML et al., Residential exposure to transportation noise in Denmark and incidence of dementia: national cohort study. BMJ 2021; 374 :n1954 <https://www.bmj.com/content/374/bmj.n1954.full.pdf> accessed 23 September 2021.
 ‘Transport noise associated with increased dementia risk’ (8 September 2021 Alzheimer’s Research UK) <https://www.alzheimersresearchuk.org/transport-noise-associated-with-increased-dementia-risk/> accessed 7 October 2021.
 Hänninen O et al., EBoDE Working Group. Environmental burden of disease in Europe: assessing nine risk factors in six countries. Environ Health Perspect. 2014;122:439-46. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4014759/pdf/ehp.1206154.pdf> accessed 24 September 2021.
 Fiona Harvey, ‘One in five Europeans exposed to harmful noise pollution – study’ (5 March 2020 The Guardian) <https://www.theguardian.com/society/2020/mar/05/one-in-five-europeans-exposed-to-harmful-noise-pollution-study> accessed 24 September 2021.
 Joe Middleton, ‘Exposure to traffic noise increases risk of dementia, study suggests’ (9 September 2021 The Independent) <https://www.independent.co.uk/news/health/traffic-noise-exposure-dementia-risk-b1916289.html#/comments> accessed 23 September 2021.