Academics at the University of Oxford’s Nuffield Department of Population Health (NDPH) have been investigating risk factors of dementia, with a particular interest in ‘speech-in-noise hearing loss’.
Difficulty hearing speech in the presence of background noise, e.g. engaging in conversation while the television is playing, is a common component of sensorineural hearing impairment [both age-associated hearing loss (presbycusis) and noise-induced hearing loss (NIHL)] and is understood to be a symptom of dementia.
Intrigued by this, the team of Oxford researchers sought to identify whether an inability to hear speech in loud environments is in fact associated with dementia.
Over 82,000 people over the age of 60 were selected to participate from the UK Biobank study.
Upon its commencement, test subjects graded themselves on their proficiency in detecting spoken numbers as white noise played, using 1 of 3 descriptors (normal, insufficient, or poor).
There were then 11-years of follow-up, during which 1,285 of the participants were diagnosed with dementia (based on hospital inpatient and death register records).
Concentrating on this section of the cohort, it was concluded that ‘insufficient’ speech-in-noise hearing was associated with a 61% increase in risk of developing dementia compared to those with ‘normal’ hearing, while ‘poor’ speech-in-noise hearing produced a 91% association, i.e. almost twice as likely.
The authors of the Alzheimer's & Dementia journal paper, documenting findings, explain that no part of the investigation was designed to probe the cause of any relationship.[i]
However, speaking with The Daily Mail, Senior Investigator, Dr. Thomas Littlejohns, speculated that hearing impairment could increase the likelihood of other dementia risk factors, which in turn increase overall dementia risk.[ii] Another possibility is that hearing impairment puts stress on the part of the brain that processes perceptual information, which could cause dementia by reducing cognitive capacity for other tasks. Alternatively, there could be a non-causal relationship, which is yet to be ruled out.
Although more research is needed, including concurrent focus on pure tone hearing impairment, it is conceivable that speech-in-noise hearing loss could be a pre-existing condition of dementia.
Experts are encouraging those concerned about their hearing to contact their GP, on the premise that speech-in-noise difficulties are a promising target for dementia prevention. Essentially, dementia may not always be inevitable.
Could dementia become a component of industrial deafness claims? We will monitor this issue closely as the volume of scientific literature grows.
[i] Stevenson JS et al., Speech-in-noise hearing impairment is associated with an increased risk of incident dementia in 82,039 UK Biobank participants. Alzheimers Dement. 2021 Jul 21. <https://alz-journals.onlinelibrary.wiley.com/doi/epdf/10.1002/alz.12416> accessed 30 July 2021.
[ii] Ryan Morrison, ‘People who struggle to hear conversations in noisy rooms are almost TWICE as likely to develop dementia, study warns’ (21 July 2021 Daily Mail) <https://www.dailymail.co.uk/sciencetech/article-9810057/Struggling-hear-conversations-noisy-room-increases-dementia-risk.html> accessed 23 July 2021.