June is Alzheimer’s and Brain Awareness Month. Approximately 50 million people around the world live with some type of dementia, the most well-known of these being Alzheimer’s disease. Specific to the USA, 5.8 million Americans are living with Alzheimer’s. Over the next decade, the prevalence of dementia worldwide is predicted to rise to 75 million.
Research has found an association between the presence of hearing loss and the likelihood of cognitive decline in adults. While further studies are necessary to figure out exactly why and how these two are linked, the previous statement may come as no surprise – Grandpa Joe definitely has a problem hearing you ask if he wants another cup of tea in addition to remembering that he had finished drinking the last one, wondering whether you had sneakily taken the last sip when he looked away.
A study conducted at two sites in Boston, MA, found that males with mild hearing loss had a 30% greater chance of reporting subjective cognitive decline when compared to those without hearing loss, and for those with moderate to severe hearing loss, this risk increased up to 54%.
How does hearing loss impact dementia?
Currently, the exact nature of the link between hearing loss and cognitive decline is murky due to numerous factors that both conditions share, such as increased age, general physical health, and cardiovascular disease. The occurrence of strokes is more common in those with dementia but is also significantly associated with moderate to severe hearing loss. Other factors such as diabetes and smoking have an effect on both cognitive ability and hearing.
One hypothesis attempting to explain the mechanics of the hearing loss-dementia relationship is known as the cognitive load theory. It is likely that everyone has experienced the effects of cognitive overload at some point – while you’re trying to wrap your head around how all that time traveling and event reversing fit together in Avengers: Endgame you’re also trying to learn some Swahili before you go on your Africa tour as well as brush up on some high school calculus to help your kids and, before you know it, you’ve put laundry detergent in the dishwasher (which is probably not the worst thing you could do). In short, the cognitive effort required to accomplish all of these noble tasks has exceeded the cognitive capacity available, to the detriment of any additional (but no less noble) tasks.
For a patient with hearing loss, the amount of concentration necessary to understand speech and surrounding auditory stimuli is greater than that required by an individual without hearing loss. This increased listening effort means that brain space and cognitive resources are constantly diverted from other tasks into processing auditory input, which is hypothesized to eventually lead to degeneration of the brain and subsequent cognitive decline. Studies have found a reduction in overall brain volume in those with sensory loss, such as hearing impairment.
An important common factor shared between hearing loss and dementia is the effect on social interactions. Understandably, those with hearing loss may withdraw from social situations and avoid conversation, potentially leading to isolation, loneliness, and depression. Social isolation and loneliness are known to be risk factors for the development of Alzheimer’s disease; conversely, frequent participation in social activities and keeping mentally active may delay the onset of cognitive decline and Alzheimer’s.
Can treating hearing loss reduce the risk of dementia?
Currently, there is insufficient evidence agreeing that the use of hearing aids or cochlear implants in those with hearing loss can significantly reduce the risk of Alzheimer’s and other dementias. In theory, if Grandpa Joe can hear more clearly with the use of hearing aids, he will keep inviting you over for tea and stimulating conversation about Avengers: Endgame, reducing his rate of cognitive decline by keeping up with his social calendar.
A commonly cited study published in 2017 by The Lancet found that treating hearing loss could reduce the risk of dementia by up to 9% – this has significant implications for Alzheimer’s, a disease considered to be the only cause of death that cannot be prevented, cured, or slowed.
Despite this, while some studies have found better scores on cognitive testing in patients with hearing aids when compared to those without, other investigations have not found a statistically significant improvement. Many of the trials investigating this area were limited by small numbers of participants and lack of demographic diversity. One potentially confounding variable in some of these studies was the suggestion that those with better cognitive function were also more likely to seek and obtain a hearing aid compared to those with existing dementia or pre-dementia.
A randomized study is currently underway in the US to assess the effects of hearing intervention on cognitive decline, known as the ACHIEVE study (Aging and Cognitive Health Evaluation in Elders). The trial has randomized 850 individuals aged 70 to 84 years without existing dementia to either receive hearing intervention, such as counselling or hearing aids, or successful aging intervention including information and physical exercise sessions with a health educator. Results are expected to be collated by 2022 and will assess cognitive decline across the two treatment groups.
The best advice for anyone noticing a decline in their cognitive ability is to talk to a qualified health professional as education and improved awareness not only for the patient but also their family and carers play a significant role in achieving the best outcomes for all involved. It is important not to ignore the signs of cognitive impairment as early intervention is associated with better quality of life even for those with an eventual dementia diagnosis. While assistance with hearing loss may or may not be part of the solution for dementia, treating hearing loss as an independent condition has the potential to improve quality of life regardless of its impact on cognitive decline.
References
Alzheimer’s Association: Alzheimer’s and brain awareness month. https://www.alzheimers-illinois.org/ABAM/
Alzheimer’s Association: facts and figures. https://www.alz.org/alzheimers-dementia/facts-figures
Hearing loss and cognitive decline: study probes link. https://www.medicalnewstoday.com/articles/324323.php
Age-related hearing loss and cognitive decline – the potential mechanisms linking the two. https://www.aurisnasuslarynx.com/article/S0385-8146(18)30458-9/fulltext
Impact of social relationships on Alzheimer’s memory impairment: mechanistic studies. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5764000/
The connection between hearing loss and cognitive decline. https://www.healthyhearing.com/report/52904-The-connection-between-hearing-loss-and-cognitive-decline
Hearing loss and cognition among older adults in the United States. https://academic.oup.com/biomedgerontology/article/66A/10/1131/686973
Aging and cognitive health evaluation in elders (ACHIEVE). https://clinicaltrials.gov/ct2/show/NCT03243422