There may be a window of opportunity to restore hearing and potentially slow dementia

Hearing loss is very common in older adults, with almost 60 per cent aged 60 years and over experiencing disabling (moderate or greater) hearing loss.

The prevalence of dementia also rises quickly with age, with more women affected than men, particularly at older ages.

For Australians aged 90 and over, women are 1.4 times more likely to have a dementia diagnosis. And in 2023, it was estimated that 411,100 Australians were living with dementia, with this number projected to more than double by 2058.

The link between hearing loss and dementia

Although cognitive decline is a natural part of ageing and doesn’t necessarily lead to dementia, older adults with untreated hearing loss experience cognitive decline at a faster rate than those without.

They’re also at greater risk of developing dementia.

Dementia risk increases with the degree of hearing loss, so people with severe-profound hearing loss (these are people who gain little benefit from hearing aids) are at greatest risk.

Despite this, and despite the serious negative impact of severe-profound hearing loss on quality of life, fewer than 10 per cent of people who are eligible for cochlear implants ever have one.

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We don’t currently know whether having hearing loss actually causes dementia, or whether it’s just associated with the condition.

But one potential reason for the link between the two conditions is that hearing loss can lead to increased social isolation as a result of communication difficulties, which may in turn result in reduced brain stimulation and loss of cognitive reserve.

Building cognitive reserve

Cognitive reserve is the brain’s ability to maintain function despite ageing and disease.

People with high cognitive reserve can maintain normal cognitive function even if they have risk factors like genetic predispositions to dementia, cardiovascular disease, build-up of proteins in the brain that restrict its function (and are thought to cause dementia), or hearing loss.

On the other hand, the presence of these and other factors may induce cognitive decline or dementia in those with lower cognitive reserve.

There are many lifestyle-related things we can do to build cognitive reserve, and it is never too late for these to make a difference.

These include exercising regularly, having a healthy diet, drinking alcohol in moderation, getting enough sleep, being socially engaged, taking up enjoyable hobbies and doing activities that use our brains (like crosswords and sudoku).

It’s currently unknown whether restoring hearing through a cochlear implant could promote cognitive reserve and delay cognitive decline.

But, as hearing loss tends to happen years or decades before clinical dementia symptoms appear, there may be a window of opportunity to restore hearing and potentially slow the development of cognitive decline associated with hearing loss.

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The COCHLEA study

The COCHLEA (Cochlear implant Outcomes and Cognitive Health – Longitudinal Evaluation of Adults) study began in 2016, led by myself in collaboration with the Royal Victorian Eye and Ear Hospital, the Mater Hospital, and the AIBL study (Australian Imaging, Biomarkers & Lifestyle Flagship Study of Ageing) at the Florey Institute of Neuroscience and Mental Health.

We compared the cognitive performance and other outcomes of a group of people with cochlear implants to another group of older adults from the AIBL study who did not use hearing aids or have cochlear implants.

We studied them over a period of four and a half years, making this study now one of the longest running in this field in the world.

Both groups were aged 60 years or older and were assessed at 18-month intervals.

We used computerised card games to assess cognitive performance both before cochlear implantation and at each follow-up interval.

Our research found that both executive function and working memory performance improved and other cognitive functions remained stable for the cochlear implant group.

In contrast, the AIBL participants (those without cochlear implants or hearing aids) declined significantly on two of the four cognitive functions assessed, despite having much better hearing.

Executive functions are higher-level cognitive skills including decision-making, planning, problem-solving and managing emotions.

Working memory means information is retained in the brain for seconds or minutes (like a sticky note for the brain), and helps with performing complex tasks like reasoning, comprehension or learning.

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Promoting healthy ageing

It’s highly unusual to see cognitive performance improving significantly in ageing adults, and for this to be sustained over several years.

Even older adults with normal hearing are expected to decline cognitively over time as part of the natural process of ageing.

The results of our study suggest that cochlear implant use may actually improve cognitive performance and/or delay cognitive decline in older adults with severe-profound hearing loss for several years, promoting wellbeing and healthy ageing.

Cochlear implants can make an enormous difference to communication ability, relationships with loved ones, awareness of the environment, independence and quality of life for people with severe-profound hearing loss.

Our findings suggest that cochlear implants can also help to improve and sustain cognitive function in this population.

So if you're worried about your hearing, or that of your parents or grandparents, organise a hearing test – it could be more helpful in the long run than you think.

We continue to welcome adults aged 60 years and over who are eligible and would like to receive a cochlear implant to participate in the COCHLEA study.

If you’re interested in taking part, please contact the research teams in Melbourne or Brisbane.

This study receives ongoing funding from Cochlear Ltd.