There is a long-established and widely recognized link between declines in sensory acuity – particularly hearing and vision – and cognition. Many studies over the years including data from the Canadian Longitudinal Study on Aging (CLSA), involving tens of thousands of participants across the country aged 45 to 85, backs this up.
Cognitive decline is associated with hearing loss, which affects about 32 per cent of people aged 55 years, and more than 70 per cent of people aged over 70 years. Hearing loss has been identified as a modifiable risk factor for dementia.
In a study that tracked 639 adults for nearly 12 years, Johns Hopkins researcher Frank Lin, M.D., Ph.D, and his colleagues found that mild hearing loss doubled dementia risk. Moderate loss tripled risk, and people with a severe hearing impairment were five times more likely to develop dementia.
Brain scans show that hearing loss may contribute to a faster rate of atrophy in the brain. One factor that could explain the links between hearing loss and cognition is the fact that sound processing and cognitive processing occur in the same areas of the brain.
A 2021 study published by the Journal of Neurology found that hearing loss in the general population is associated with lower baseline levels of cognitive function and decreased performance on memory tests over time—although more research is needed before scientists can definitively name hearing loss as a risk factor for cognitive decline.
Findings from another study showed that individuals with hearing loss developed between 30% and 40% acceleration of cognitive decline and 24% increased risk for incident cognitive impairment during a six-year period compared to those with normal hearing. They also found that individuals with hearing loss would require 7.7 years to decline five points on the cognitive scale versus 11 years in individuals with normal hearing.
Not only do studies suggest that older people with hearing loss are more likely to develop Alzheimer’s disease and dementia, but they also found that hearing loss can be associated with a faster rate of cognitive decline*. Why is this?
Researchers have several theories:
- One has to do with cognitive load. With untreated hearing loss, the brain gets overworked by constantly straining to understand speech and sound. An overworked brain doesn’t work efficiently.
- Another has to do with brain structure. Brain cells can shrink from lack of stimulation, including the parts of the brain that receive and process sound.
- The last theory is social isolation. When a person has trouble hearing conversations and socializing, they may prefer staying home instead. However, the more isolated a person becomes, the less stimuli their brain receives.
The good news is that studies show that the proper use of hearing aids can lower the risk factor of dementia. In fact, another study documented hearing loss and cognitive decline among a group of nearly 4000 volunteers over a 25-year period. What researchers found was interesting — people with hearing loss who didn’t use hearing aids had a higher risk of dementia and depression. However, people with hearing loss who did use hearing aids experienced cognitive decline at a rate similar to people without hearing loss. The researchers concluded that the key wasn’t simply the ability to hear better but, more importantly, how better hearing allowed them to stay involved in everyday life. By restoring the ability to better communicate, hearing aids can help improve social interactions, mood, and provide the opportunity to participate in brain-stimulating activities that can help slow cognitive decline.
After 18 months of hearing aid use, researchers found speech perception, self-reported listening disability and quality of life had significantly improved for participants. Most notably, 97.3 per cent of participants in this study showed either clinically significant improvement or stability in executive function -- their mental ability to plan, organise information and initiate tasks. Women, in particular, showed significant improvements in working memory -- used for reasoning and decision-making -- as well as most other cognitive functions assessed. The study also found more frequent use of hearing aids was associated with greater improvements in cognitive function, and women were much more diligent at wearing the devices than men.
Visual impairment (VI) also is an age-related condition and is estimated to affect more than 1 billion individuals worldwide by 2050. It is the third leading cause of disability for the elderly and also has substantial physical, psychological, and social implications on patients and society overall. Interestingly, VI has been suggested as one of the early symptoms of dementia.
Many studies have reported similar microvascular and neuronal changes in the eye and brain in patients with cognitive impairment or dementia. One research team investigated the association between cognitive and vision impairment in elderly populations by analyzing two large U.S. population data sets — over 30,000 respondents from the National Health and Aging Trends Study and almost 3,000 respondents from the National Health and Nutrition Examination Study — which both included measurements of cognitive and vision function. After adjusting for hearing impairment, physical limitations, patient demographics, socioeconomic status and other clinical comorbidities, we found an over two-fold increase in odds of cognitive impairment among patients with poor vision. Other studies have found this impairment to be up to 5x greater.
In particular, decreased scores on cognitive tests were found in those with glaucoma, whereas those with macular degeneration showed weaker brain functionality. Investigators have found significant associations between lessened brain functions and age-related macular degeneration (AMD). 5604 people age 40+ who participated in the 2005-2008 National Health and Nutrition Examination Survey have been found to experience increased memory problems and confusion, seemingly as a result of their AMD. The report was published in the December 2019 issue of the British Journal of Ophthalmology. People with any level of AMD were found to have 1.62-fold higher odds of having self-reported cognitive difficulties compared to those without AMD. Likewise, patients with early and late AMD were associated with significantly higher reporting of memory problems. Seniors who are cognitively impaired are up to twice as likely to have AMD.
Individuals who lose vision at an older age may have difficulty doing visually intensive cognitive activities that they enjoyed before they lost their vision (e.g., reading, driving, knitting, cooking, etc). Studies have in fact found that older adults with lower levels of visual acuity have reduced levels of leisure-time activities. This could over time lead to the loss of an active cognitive reserve and a diminished cognitive performance.
It may be possible to reverse or prevent this process in people with vision loss. The good news is that individuals with baseline vision impairments that improved to normal vision and those who vision remain normal over 6 years had significant lower magnitude of decline and causing the function. Cataract surgery for an example, improved visual outcome and was associated with improved cognitive performance and with increased gray matter volume in the cortex.
Poor vision and hearing impairments have been shown to lead to a cognitive decline at a faster rate than normal aging but research shows that correcting these deficits can bring a person back to the aged peers when corrected early enough. Ensuring regular cognitive check ups as well as hearing and vision tests is important to maintain proper cognitive health.
Book your comprehensive cognitive assessment at Honsberger Physio+, including screening tests for macular degeneration using the M&S Technologies system.
Athletic Therapist (retired)