Hearing loss and decline in cognitive function leading to dementia are prevalent in the elderly population. Both affect quality of life, and many studies suggest that both conditions are related, and that hearing loss may be a risk factor for development of dementia in older adults.
The first report that brought to attention association between hearing loss in older adults and the probability of developing dementia was published by Uhlman in 1989.1 Since then, multiple studies have been conducted further clarifying this intriguing relationship.
With the increase in longevity, the challenging relationship between aging and neurodegenerative diseases has been getting increased attention by the scientific world. At the sub-cellular level, failure of the ubiquitin-proteasome system to degrade and eliminate amyloid beta, either due to malfunction or overload of the degradation and elimination processes, plays a role in many neurodegenerative diseases (Alzheimer’s disease, encephalopathies like CJD, Huntington disease). 2,3
That is one of the many attempts to understand the mechanisms of how the amyloid-beta peptide became the main suspect as a causative factor in cognitive decline and eventually Alzheimer’s disease. Functional MR studies of the brain showed significant reduction in cortical activity and reduction in neural specialization of the ventral visual cortex in older adults.4
We are all aware of the fact that hearing-impaired older adults face some form of social isolation. Social connections with friends start suffering first, and later with family members as well, possibly due to higher tolerance of the condition by family members who, because of day-to-day interactions with the person, may not recognize a gradually progressive mental decline. At the same time, family members are also the first to suggest to the patient to seek hearing evaluation.
This association of hearing loss with gradual cognitive decline caught the attention of researchers who were studying Alzheimer’s, and they soon found that people with hearing loss had a higher chance of developing dementia. Simultaneously, hope arose that improvement of hearing by providing hearing aids or cochlear implantation could slow down, or even reverse, cognitive decline. A large study published in JAMA in 2019 that included 16,270 individuals, half with and half without hearing loss, showed that hearing loss was positively associated with accelerated cognitive decline and incident dementia, especially in patients aged 45-64 years.5 In the study, hearing loss included presence of peripheral hearing impairment and impairment in central auditory processing.
In a comprehensive review of 17 articles that studied association of hearing loss using pure tone audiometry testing and dementia using Mini Mental State Exam, the authors concluded that hearing loss is associated with a higher incidence of dementia in older adults.6
The causal link of how hearing loss increases the risk for dementia is not well understood. The theories suggest the following relationships and causes.
1. Theory of Information Degradation. This postulates the following: normal hearing in an individual with normal cognition is associated with minimal mental effort that is primarily directed towards correct understanding of the auditory verbal message. If hearing loss is present, especially if it is progressive, as is the situation with age-related hearing loss, the individual will grapple with difficulties to maintain the same degree of understanding as it used to be when the hearing was normal. Ever greater brain resources that are being mobilized to maintain focus on hearing and understanding will at the same time be taken away from other mental tasks leading to cognitive involution. With the struggle to hear, the patient will experience global information degradation needed for normal orientation in space and time.
2. Common Pathophysiological Pathway. The second hypothesis suggest that there is a common pathophysiological pathway that affects hearing and cognitive function. Since there are patients with dementia who do not have hearing loss, and since there are patients with hearing loss who never develop dementia, this theory has little support. For the same reasons, the theory that cognitive decline leads to impaired auditory perception has even fewer supporters.
3. Theory of Sensory Deprivation. This postulates that hearing loss leads to cognitive deprivation and further progresses into cognitive decline, finally spiraling into dementia. Over time, people with hearing loss start withdrawing from conversations since they become more and more difficult to follow. Such social disengagement results in diminishing environmental input needed to keep the patient informed about up-to-date life events in general, and social interactions will suffer even more.
The named theories are further burdened by the presence of covariables that are inherent to older age. Cardiovascular disease, diabetes, high cholesterol, hyperlipidemia, hypertension, smoking, possible presence of Apolipoprotein-E allele are all factors that affect the aging brain and contribute to cognitive impairment. Hearing loss appears to be the least studied covariable, and only recently studies have focused on the contribution of hearing loss to brain pathology. Imaging studies suggest that patients with hearing loss showed accelerated rate of brain atrophy, especially in areas of the brain that are responsible for processing sound and speech (superior, middle and inferior temporal gyri).
Research so far definitely points to a strong association between hearing loss and dementia, but we still cannot say that hearing loss causes dementia.
Furthermore, even mild hearing loss is associated with a doubled risk for dementia compared to a control population of the same age without hearing loss.7 Moderate hearing loss tripled such chance, while severe hearing loss made onset of dementia five times more likely.
While hearing aids and cochlear implants (CIs) can improve not only hearing but also pre-intervention cognitive scores and help hard-of-hearing individuals reengage with family and friends, the studies have yet to show if such intervention can actually slow down or fend off cognitive decline and dementia. In light of this interesting relationship between hearing loss and dementia, hearing loss is not looked at anymore only as an inevitable fact of aging. Instead, it’s acquired a new dimension for predicting the chance of developing dementia. Further research should provide a better understanding of this challenging relationship for neuroscientists, epidemiologists, audiologists and ENTs. In the meantime, otolaryngologists and audiologists are encouraged to identify patients with hearing loss in patients 45 years and older and explain the importance of early intervention, including counseling, education and provision of hearing aids.
1.Uhlmann RH, Larsen EB, Rees TS, Koepsell TD, Duckert LG. Relationship of hearing impairment and cognitive dysfunction in older adults. JAMA. 1989, Apr 7; 261(13):1916-9
2. Hong L, Huang HC, Jiang ZF. Relationship between amyloid-beta and the ubiquitin-proteasome system. Neurol Res. 2014 Mar.; 36(3):276-82
3. Alves-Rodrigues A, Gregori A, Figueiredo-Pereira ME. Ubiquitin, cellular inclusions and their role in neurodegeneration. Trends Neurosc. 1988, Vol 21, Issue 12, 516-520
4. Park DC, Polk TA, Park R, Minear M, Savage A, Smith MR. Aging reduces neural specialization in ventral visual cortex. PNAS. 2004, 101 (35) 13091-13095
5. Liu CM, Tzu-Chi C. Association of hearing loss with dementia. JAMA Network open. 2019;2(7)
6. Thomason RS, Auduong P, Miller AT, Gurgel RK. Laryngoscope Investig Otolaryngol. 2017 Apr; 2(2):69-79
7. Lin FR, Metter JE, O’Brien RJ, Resnick SM, Zonderman AB, Ferrucci L.
Hearing loss and incident dementia.
