There is a link between hearing loss and dementia – as hearing loss increases in severity, so does the risk of developing dementia [1].
A Lancet commission on dementia (updated in 2020) identified a number of risk factors. Some of these risk factors are potentially modifiable – that is, if something is done to address them, it might be possible to reduce the risk of dementia. Hearing loss in mid-life was the biggest of these risk factors, accounting for 8.2% of the total risk of dementia [2].
It is important to understand the link between hearing loss and dementia because:
- If hearing loss is a cause of dementia, then by diagnosing and addressing hearing loss earlier, we might be able to reduce the risk of dementia.
- Understanding the link could help us develop better treatments for both conditions, or help us detect the development of dementia sooner.
Since 2018, we’ve been working with Alzheimer’s Research UK, the UK’s leading dementia research charity, to fund research to understand this link. Together, we’ve invested more than £850,000 into this area of research, with more planned for the coming years. For 2023 we decided to take stock of developments in the field by hosting an online workshop for hearing and dementia researchers to discuss the latest science. Over 100 researchers attended the workshop on Wednesday 1 March.
Genetic studies to better understand the link between hearing loss and dementia
Professor Sally Dawson from the UCL Ear Institute spoke about how we can use genetics to better understand the link. Using genetic data from large studies of ageing, she has been looking for common inherited factors that could explain this link. Her work so far has shown no genetic evidence to support the idea that hearing loss causes dementia (or vice versa), or that there is a shared underlying cause.
However, her research suggests that there may be common processes underlying both conditions linked to signalling chemicals used to send messages in the brain. She has also found evidence to support the idea that there is a more complex link between hearing loss, dementia and other conditions such as diabetes and cardiovascular disease.
The role of the brain’s blood supply in the link between hearing loss and dementia
Dr Nicolas Michalski from the Institut Pasteur in Paris, France spoke about his investigation into whether the brain’s blood supply underlies the link between hearing loss and dementia. Together with Dr Nicolas Renier he is studying whether hearing loss causes changes to the brain’s blood supply that could then speed up the development of dementia. Using high-resolution microscopy techniques they have been studying the blood supply to auditory regions of the brain in mice and the impact of hearing loss on this system.
They have shown that hearing loss causes auditory regions of the brain to have fewer blood vessels, and thus a less robust blood supply. They are investigating whether age-related hearing loss could therefore trigger a cascade of changes to the brain’s blood supply that ultimately leads to dementia. They will also investigate whether treating hearing loss can reverse these changes and potentially help to prevent dementia.
Measuring hearing processes in the brain may improve our understanding of the link
Professor Jason Warren from the Dementia Research Centre at UCL spoke about how changes in hearing (particularly changes in how the brain processes sound information, rather than how the ear detects sound) could be an early warning sign for the development of dementia. He also emphasised how it’s not just hearing parts of the brain that are interested in sounds – many other parts of the brain also process sound information. Often, these parts of the brain are the ones that are targeted by dementia.
His takeaway message was that it is likely to be important to focus on central (brain) as well as peripheral (ear) measures of hearing when trying to understand the link between hearing loss and dementia, and in developing treatments.
Testing whether hearing aids can reduce the risk of dementia
Dr Sergi Costafreda Gonzalez from UCL spoke about his research to understand whether treating hearing loss with hearing aids can reduce the risk of dementia. The use of hearing aids has been associated with slowing cognitive decline in people with hearing loss and may therefore also reduce the risk of dementia. However, to prove this definitively and to understand the extent to which hearing aids can reduce the risk of dementia, robust clinical trials are needed.
In the TACT pilot clinical trial, Sergi’s team tested a new intervention for fitting hearing aids in people with hearing loss and mild cognitive impairment. This involved a series of home visits from an audiologist along with the provision of rechargeable hearing aids. The results from the trial suggested that people with hearing loss and mild cognitive impairment need more tailored support to use their hearing aids than the standard NHS pathway provides. Their results also suggested that the provision of hearing aids could improve cognition – supporting the need for a full clinical trial to understand if hearing aids can reduce the risk of dementia.
Panel discussion
The workshop was chaired by Dr Bob Carlyon, an auditory neuroscientist at the University of Cambridge, with an interest in understanding how the brain processes sound and using that knowledge to improve how cochlear implants work. He hosted a question-and-answer session with the four speakers, and the audience were invited to submit questions.
Much of the discussion centred on the need for larger research studies and trials to better define the nature of the link between hearing loss and dementia, and the impact of treating hearing loss on dementia risk.
Panellists also highlighted the need for clinicians to be aware of the link, and the importance of ensuring that people with dementia and hearing loss were referred to receive hearing aids.
The workshop ended with a promotion of our joint call for applications in this area of research, through RNID’s Discovery Research Grant scheme, which is accepting preliminary applications until Wednesday 19th April 2023.
References
- Lin, FR. et al. (2011) Hearing loss and incident dementia. Arch Neurol, 68(2):214-220. https://doi.org/10.1001/archneurol.2010.362
- Livingston, G. et al. (2020) Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. Lancet, 396:413-446. https://doi.org/10.1016/S0140-6736(20)30367-6
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