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Research review: Hearing loss and cognitive decline

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By Rex Banks, Au.D., Reg. CASLPO
Doctor of Audiology
Director of Audiology at CHS

For the past two decades, audiologists have suspected that there is a significant correlation between uncorrected hearing loss and reduction in cognitive functions in older adults. Drawing a link between the two has gained much attention in the audiology world in recent years. There are many relevant research studies that examine hearing loss and cognitive function.

What do all these studies tell us?
Some researchers suggest that a common pathology may cause both conditions or that the strain of decoding sounds over the years may overwhelm the brains of people with hearing loss, leaving them more vulnerable to dementia. Also, hearing loss could lead to dementia because individuals may become more socially isolated, a known risk factor for dementia and other cognitive disorders.

So what should you do? 
Although research points to a link between hearing loss and cognitive decline, researchers are still trying to figure out the reason for this link. If you have some hearing loss and decide to go for a cognitive assessment, be sure to tell the tester about your hearing loss. The test will be more accurate if you hear as well as possible during the test. Most importantly, if you think you have a hearing loss, go for a hearing test. If hearing aids are recommended, take action sooner than later. Hearing aids will help you stay involved and connected to others.

For a complete hearing assessment and to talk about your communication goals, contact an audiologist at the Canadian Hearing Society.

Here is a review of the most recent/relevant research:

  • Baltimore Study on Aging 2011

One of the first studies to test the theory that hearing loss was a risk factor for dementia was the 2011 Baltimore Study on Aging. This study followed 639 people and found that compared to those with no hearing loss, people with mild, moderate or severe hearing loss had respectively a two, three and five time increased risk of developing dementia based on the severity of hearing loss.

  • The ABC Health Database 2013

In 2013, a study from The ABC Health Database indicated that those with hearing loss had a 30-40% faster rate of loss of thinking and memory abilities compared to those with no hearing loss. The study suggested that hearing loss was associated with faster cognitive decline and related cognitive impairment in older adults who live in a community or independently.

  • Hearing loss linked to brain tissue loss 2014

A brain imaging study in 2014 on a sample population from the Baltimore Study on Aging found that people with hearing loss had accelerated brain tissue loss in whole brain and regional brain tissue in the right temporal lobe of the brain, the structures responsible for processing sound and speech.  The study concluded that older adults with hearing loss may have a faster rate of brain shrinkage as they age. 

  • Self-Reported Hearing Loss: Hearing Aids and Cognitive Decline in Elderly Adults: A 25-year Study 2015

A study published in October 2015 is the first to show that wearing hearing aids reduces cognitive decline associated with hearing loss. This was a 25-year study that followed 3,670 adults, age 65 and older.   The study included three groups of subjects: those who did not report hearing loss (considered the control group); those with hearing loss who did not use hearing aids, and those with hearing loss who did use hearing aids.

The researchers compared the rate of cognitive decline among these groups and found no difference between the control group and those who used hearing aids, but did find those with untreated hearing loss had lower scores on a test of cognitive function.

Conclusion
While research indicates that there is accelerated cognitive decline in older adults with hearing loss, we cannot yet say that hearing loss causes cognitive decline. So far, research links the two as associative, not causal. Cognitive decline could be explained by social isolation and depressed mood, which develop gradually in elderly people with hearing loss. Other studies suggested further research on whether hearing rehabilitative interventions such as hearing aids could affect cognitive decline. It could be concluded that using hearing aids positively affects cognition by restoring communication abilities which in turn promoted continued social and leisure activities, and quality of life. Research on this topic is ongoing and continues to evolve. Tune in to CHS Connections for future updates.

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