Abstract
Introduction
Research has suggested that age-related hearing loss (ARHL) may increase the risk of dementia, an incurable and prevalent condition. Unlike dementia, ARHL is prevalent but undertreated and modifiable. In the absence of a cure and under the pressure of an ageing population, preventative strategies targeting dementia are crucial. This review therefore explores the association between ARHL and dementia in more depth and considers the evidence that hearing interventions such as hearing aids (HAs) may reduce the subsequent risk of dementia.
Method
A comprehensive search strategy was used in four online databases (PUBMED, EMBASE, Medline and PsycINFO) in addition to cross-referencing. Selection criteria were then applied to search results, followed by the screening of titles and abstracts, quality assessment and content analysis using NVivo.
Results
Six broad hypotheses, with varying degrees of support, explain the ARHL-dementia association as either causal, common or reverse causal. Causal mechanisms linking ARHL to dementia involve information degradation, sensory deprivation or an increased cognitive load on perception, whereas common pathways suggest a third variable underlies both conditions. Preclinical dementia pathology may also cause hearing loss on a reverse causal pathway, or it may be that ARHL impedes cognitive test performance, leading to dementia overdiagnosis. In terms of prevention, evidence is mixed, inconsistent and largely based on observational data, with a lack of corroboration from randomised controlled trials (RCTs). Whilst some studies show a protective effect against dementia through HA use, others have shown no significant neurocognitive benefit.
Conclusion
Although plausible, individual hypotheses are insufficient in explaining the ARHL-dementia link; pathways likely interact and cascade together. Without a definitive mechanistic pathway, the therapeutic potential of this association remains unknown. To fully appreciate the power of HAs in preventing dementia, larger RCTs with extended follow-up periods and comprehensive cognitive test batteries are needed.
Comments
Outcome measures
This is an interesting project and demonstrates that even where there is high plausibility, therapeutic relationships are often more complex. I’m curious whether the literature you reviewed primarily focuses on cognitive screening tools (e.g. the MMSE), or if it also includes more functional assessments such as ADL measures or evaluations of loss of independence.
Re: Outcome measures.
Thank you for your comment. My project primarily focused on cognitive outcomes in individuals with hearing loss following intervention with hearing aids or cochlear implants. Most of the studies reviewed used screening tools such as the MMSE or MoCA to assess cognitive change. I did not specifically explore functional assessments, including ADL measures or evaluations of independence, but I agree that this represents an important area for further investigation. The project did consider social deprivation as a potential mechanism linking hearing loss and cognitive decline, and a broader examination of functional and psychosocial factors would add valuable context to future research in this area.
Re: Outcome measures.
Thank you for your comment. My project primarily focused on cognitive outcomes in individuals with hearing loss following intervention with hearing aids or cochlear implants. Most of the studies reviewed used screening tools such as the MMSE or MoCA to assess cognitive change. I did not specifically explore functional assessments, including ADL measures or evaluations of independence, but I agree that this represents an important area for further investigation. The project did consider social deprivation as a potential mechanism linking hearing loss and cognitive decline, and a broader examination of functional and psychosocial factors would add valuable context to future research in this area.
Excellent overview of a…
Excellent overview of a complex topic. You note that a limitation is a lack of consistency in the measures being used. A PhD student in Nottingham is developing a Core Outcome Set for dementia and hearing research. Hopefully this will help address this limitation in the future,
Interesting
Interesting think another limitation to the current research base might be reliance on pure tone audiometry vs assessment of central hearing integration.