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Is there a link between hearing loss and cognitive decline?


There has been much discussion recently about the link between hearing loss and cognitive decline. So much media attention suggests there is clear evidence to support the notion that hearing loss causes such decline. But whilst the association has been well known for decades, to suggest that acquired deafness causes this decline and more specifically causes dementia and alzheimers is not completely accurate. Further reports that hearing aids can reduce or even reverse this decline is, at best, misleading. But let's take a look at the reports first.

The University of Bordeaux in France have undertaken a 25 year study comprising 3,777 adults aged 65 years and older. There were 3 main subject groups in the study: those suffering with major hearing loss; those with moderate hearing loss; and those with no hearing loss. The study showed that there was a greater cognitive decline amongst those who experienced some degree of hearing loss. They also found that those adults with hearing loss that wore hearing aids scored better in cognitive tests than those without hearing aids.

The John Hopkins University in Baltimore have published research looking at how hearing loss is linked to accelerated brain tissue loss. 126 participants in the study underwent yearly MRI (magnetic resonance imaging) scans over the course of 10 years. They did indeed find that those adults with impaired hearing lost more than an additional cubic centimetre of brain tissue than those with normal hearing.

Other studies claim that adults with untreated hearing loss are two, three or five times more likely to develop dementia, depending on the severity of their hearing loss. Others claim that adults with hearing loss experience a 30%-40% greater decline in cognitive abilities when compared to their counterparts without hearing loss. The same study also found that adults with hearing loss develop significant impairments to their cognitive abilities 3.2 years earlier than adults with normal hearing.

There is no denying that hearing loss can be debilitating at best and life changing at worse. As an audiologist, I have seen first hand the impact hearing loss can have on an individual and their loved ones. To describe someone as being deaf is slightly ambiguous. There are different types of hearing loss and different degrees of hearing loss. Where one person may experience a mild hearing loss and appear to manage with relative ease, another may be completely debilitated. What we do know is that hearing loss left untreated can have huge impacts on an individuals social, physical and mental well-being. And although hearing loss is not life threatening it is most certainly life changing. What all these studies confirm is that there is an association between hearing impairment and cognitive decline but not that hearing impairment causes it. The association might well be because they share common causes such as lifestyles: diet, exercise, smoking. In addition, a persons genetic susceptibility and of course any age related factors such as cardiovasular disease and inflammation.

As the blog title says, we hear with our brain and not our ears. Our ears collect incoming sound waves, convert that acoustic energy into mechanical (middle ear) energy and then electrical (inner ear) energy in the form of electrical impulses which stimulate the acoustic nerve and send that incoming information to the brain. This conversion of energy is simply the process of converting incoming sound information into the language that the brain understands. Each sound we hear stimulates a particular place in our cochlea (inner ear) and each place corresponds to a particular frequency of sound. The footprint of each sound we hear is stored in our memory bank ready to create responses both physical and emotional. As the hearing pathway becomes compromised or damaged, the brain doesn't receive the same information and thus has to reorganise those footprints. The worse the hearing loss the less information the brain receives. Over time not only do we forget that we can't hear certain sounds but we may also start to stop pronouncing them at all. As I said before, an individuals experience of hearing loss creates some very negative emotional responses that can leave them feeling lonely, scared and vulnerable. It is all these factors which can contribute to bigger problems.

When we lose our hearing, we lose the ability to hear certain sounds around us. We might think that the primary impact of losing our hearing equates to missing speech sounds or mishearing speech. However, the impact of being unable to hear environmental sounds is just as great. Imagine not hearing the birds tweeting in the morning or being able to listen to your favourite music. Then think about not hearing a car approaching as you cross the road, or your baby crying when you go to sleep at night. The impact is far reaching and has different consequences. People with hearing loss describing how they feel about their hearing loss will often say they are embarrassed, anxious and upset but over time these feelings can develop into a fear of not being able to cope, an increasing desire to withdraw and distress.

If we know that hearing aids improve auditory functioning then they may help someone with dementia to function better and live a more independent life. If this is the case they may live a little longer than otherwise. Correcting hearing loss with hearing aids or hearing implants has a direct and indirect on a persons ability to manage themselves and the world they live. They give independence, improve confidence, provide inclusion and maintain an ease of listening that has huge health benefits both emotionally and physically. My advice, definitely have your hearing checked if you are in any doubt and if you have a hearing loss, listen to the recommendation and take action if necessary. The benefits it would seem are bountiful.


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