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How does your hearing affect dementia risk?

Explainer

Ellen Mcintosh

On 25 August 2023

An important study reviewing risk factors for dementia suggested people with unaddressed midlife hearing loss may be more likely to have the condition than those without hearing loss.

With around 1 million people living with dementia in the UK, and more than 12 million people estimated to have a type of hearing loss, it’s never been more important to understand this link.

Is the answer in our blood?

One way that hearing loss and dementia could be linked is through our blood system.

Certain types of dementia, particularly vascular dementia, are caused when blood flow to the brain is restricted. This can damage our brain cells. Recent studies have also shown that the parts of our brain that process sounds (our auditory system) are particularly vulnerable to damage.

With funding from Alzheimer’s Research UK, Dr Nicolas Michalski is working to understand this link at Institut Pasteur in France. He’s investigating how changes in the blood supply to the brain is linked to hearing problems and in turn, whether this could impact dementia risk.

Or is it inflammation?

Inflammation in the brain is a growing area of interest for scientists tackling dementia. We know that the brain has specialised immune cells to protect it from harm, just like the rest of our body.

But research shows that in dementia, this process can actually end up causing more damage.

Dr Brian Allman and his team at the University of Western Ontario are trying to find out whether inflammation in the brain is the missing piece in the dementia and hearing loss puzzle.

Funded by Alzheimer’s Research UK and The Royal National Institute for Deaf People (RNID), his team is trying to understand whether hearing loss caused by noisy environments causes damage to the brain, triggering inflammation. They are interested in whether this could speed up memory problems that normally occur in old age, and also affect the changes in the brain that cause Alzheimer’s disease.

Dr Allman presented his team’s tentative findings at the 2023 Alzheimer’s Research UK conference. They show that, in mice, exposure to loud noise in early adulthood can in fact have long-lasting impacts on brain function in later life. More research is needed to understand how the effect is linked to dementia.

A direct or indirect link?

Social isolation is another known risk factor for dementia, and a third area of research is looking at whether hearing loss indirectly affects dementia risk by making it harder for people to stay connected.

We know that regular mental activity and social connection can help to build a person’s ‘cognitive reserve’. This is the brain’s ability to cope when it’s faced with challenges, including the diseases that cause dementia. So it’s possible that hearing loss affects a person’s ability to build and protect their cognitive reserve, and in turn, increases their dementia risk.

Other studies have suggested that there is a more direct link between hearing loss and dementia. They found that people with hearing loss dedicate more of their brain’s resources to helping them process sounds, but this can be at the expense of other cognitive processes like memory.

Alzheimer’s Research UK has partnered with the RNID to fund a research team at the University of Manchester to unpick whether hearing loss is linked to dementia directly or indirectly. They’re also looking at whether hearing aids can play a role in reducing dementia risk.

Father and daugher on a bench

The cocktail party effect

Most previous studies have focused on our ability to detect sounds, but a new area of research focuses on the ‘cocktail party effect’. This is the challenge people have focussing on a single speaker or conversation in a noisy environment. In a third project jointly funded by Alzheimer’s Research UK and the RNID, Prof Jason Warren’s team at University College London to investigate whether this could be an early warning sign for dementia.

Protect your hearing

So, what steps can you take to look after your hearing?

If you’re exposed to excessive loud noises through work, make sure you protect your ears as best you can. You can also complete the RNID’s free online hearing check or visit your doctor if you have any concerns about your hearing. Specialists are able to discuss the benefits of hearing aids and other treatments for people who will benefit from them.

Interested in finding out more about dementia and hearing loss? Listen back to our Lab Notes talk, where we discuss the topic with two leading dementia researchers.

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