Findings from the last 25 years indicate that changes in hearing ability have a direct impact on cognitive (mental) ability. Over time, hearing loss increases the risk of developing dementia.
What is age-related hearing loss?
Age-related hearing loss is called "presbycusis," from the Greek words for old (presbys) and hearing (akousis). It is a gradual, progressive process of hearing loss that occurs in people with increasing chronological age. It is usually a bilateral, symmetrical process of sensorineural hearing loss due to degeneration of the inner ear structures as a person begins their sixth decade.
Hearing loss is first felt in relation to high frequencies and is characterized by reduced sensitivity (to quieter sounds) and word comprehension (words are perceived distortedly). At the same time, the person has difficulty regulating sounds and noises in a noisy environment, during conversations and enjoying music. All of this affects social participation.
What is the prevalence of age-related hearing loss?
The prevalence of hearing loss doubles every decade, so that approximately two-thirds of people aged 70+ suffer from significant hearing loss, which impairs daily communication.
As the world's population ages, the number of people with hearing loss is increasing rapidly. It is estimated that there are approximately 466 million people worldwide with hearing loss, and the number is predicted to increase to 630 million by 2030 and to more than 900 million by 2050.
However, less than 20% of adults with hearing loss access treatment, namely hearing aids. People with hearing loss who regularly use hearing aids are generally healthier and of higher socioeconomic status.
What is the connection between age-related hearing loss and dementia?
Hearing loss has recently been identified as a risk factor for dementia. Research findings have found that hearing loss itself constitutes an increased risk of dementia in people without prior cognitive decline.
What is the explanation for the link between hearing loss and dementia?
There are several hypotheses regarding the mechanism linking age-related hearing loss and cognitive decline.
Cognitive reserve reduction: The concept of cognitive reserve suggests that each person has the ability to adapt the thinking systems in the brain as well as different thinking strategies to cope with neurodegeneration, such as Alzheimer's disease. Research shows that people with age-related hearing loss invest more cognitive resources in decoding sound and audio signals at the expense of other thinking processes, such as short-term memory.
Using neural resources to decode auditory signals and emptying the cognitive pool may lead to early signs of dementia. When the reduction of neural resources in adults with age-related decline is also accompanied by changes in attentional focus, short-term memory, and information processing speed, this has a significant impact on a person's everyday communication in their attempts to understand speech they hear.
Social isolation: Another pathway that could explain the link between age-related hearing loss and dementia is related to social isolation. Age-related hearing loss increases a person's risk of social isolation, due to difficulties in communication, and social isolation itself is known to be a risk factor for dementia.
Longitudinal studies, epidemiological models, and brain disease studies have shown that weak social networks, low social support, and feelings of loneliness increase the risk of dementia. It is hypothesized that a broad social network acts as a protective factor against cognitive decline through intellectual and emotional stimulation, as well as practical support.
The risk of dementia associated with age-related hearing loss increases when hearing loss reaches a level of 25 decibels or more (mild loss or greater). This is the accepted threshold at which hearing loss affects verbal communication.
Changes in brain structures: The most common model for assessing the relationship between age-related hearing loss and dementia is related to changes in brain structures, measured in relation to the volume of the brain using MRI scans. Several studies have found that older people with hearing loss have smaller volumes in key auditory areas of the cerebral cortex, as observed on MRI. It is hypothesized that this is related to reduced stimulation of the area by auditory signals (they simply weren't being received).
The increased reduction in brain volume in people with age-related hearing loss compared to people with normal hearing is also found throughout the brain. There seems to be a significant effect of the volume reduction in the right lateral lobe, in particular, where important areas for processing language and auditory information are located. These areas are known to be important not only for processing spoken language, but also for certain types of memory and sensory integration. It is possible that volume loss in areas responsible for processing auditory information also affects other cognitive functions that depend on these same areas, thereby increasing a person's risk of developing dementia.
Vascular diseases: Diseases of the thin blood vessels may lead to a lack of blood and damage to the structures inside the ear and affect them in the same way that a lack of blood, oxygen, glucose, and other essential substances affect the brain. In other words, just as a lack of essential substances and blood may lead to cerebral events of various magnitudes (from microscopic to large), so too may changes in the blood vessels in the head lead, over time, to changes in the blood supply to the delicate structures in the ear and, against this background, damage to these structures.
What should you do?
1. It is recommended to get tested when you experience the beginning of a change in hearing loss: If those around you tell you that you have a hearing problem – go get tested!
2. Regular and consistent use of custom-fitted hearing aids is the best way to positively impact age-related hearing loss and the cognitive ability that is affected by it. Use your hearing aids!
Sources:
Lin, FR & Albert, M. (2014). Hearing Loss and Dementia – Who's Listening?. Aging Mental Health, 18(6): 671–673.
Chern, A. & Golub, JS (2019). Age-related hearing loss and dementia. Alzheimer Disease and Associated Disorders, 33(3): 285–290.