Opinion: You may have heard that the number of people with dementia is set to double in the next two decades. You can also assume an ageing population is likely to be hard of hearing, and that our memory and collective cognition will become poorer with age. But could age-related cognitive decline be related to hearing loss? And, if so, could hearing aids slow age-related cognitive decline?

There’s a good chance it would. An increasing number of studies have found a relationship between cognitive ability and hearing loss. A review in the Lancet journal, for instance, indicated that 8 percent of dementia cases could be attributed to hearing loss at mid-life. This percentage may not sound high but the next highest modifiable factor (excluding genetically inherited risks for dementia) was smoking, at 5 percent.

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Untreated hearing loss has been identified as a risk for more rapid cognitive decline as we age, but there is compelling evidence hearing aids could help, not only to preserve our ability to hear, but also preserve, even improve, our ability to think. (It’s important to note this research relates to people who lose hearing, not to people born deaf, who use sign language.)

Exactly how hearing loss could lead to cognitive deficit is complicated and hard to untangle. Which comes first, the loss of hearing or the cognitive decline, or is it a continuous negative feedback loop?

There are several theories. The “sensory deprivation” hypothesis argues that cognitive decline is related to lack of brain stimulation – like most parts of the body, our neural networks need to be activated, which includes the parts of the brain that process sound. The “information degradation” hypothesis is similar, although argues that cognitive decline is the result of the brain working so hard processing sound that it has less capacity to perform cognitive tasks.

The benefit on cognition in our study did not depend on the cost of hearing aids. The evidence points towards the ability of the audiologist to select the most appropriate hearing aids for the job, not how expensive they are

Another theory suggests that hearing loss and cognitive decline are because of changes in brain structure or function, or both. It’s quite likely a combination of all theories is behind the connection between hearing loss cognitive decline.

Studies looking at older populations without hearing loss, those with hearing loss, and those with hearing loss using hearing aids have found that people with normal hearing or using hearing aids have better cognition than those with hearing loss and not using hearing aids. These types of studies cannot say that cognition is better just because of the hearing aids, as there may be other factors involved, such as wealth or education. But studies that test cognition before and after hearing aid use that control for other factors also support hearing aids (good hearing in general) for healthy ageing and cognition.

Intuitively this makes sense; being able to hear means being able to interact with others, which aids psychosocial health. But it also has a biological basis. The hearing system is always on – it is filtering out sounds that are unimportant and focusing on those we need to attend to, and this requires brain power. What is that sound, where is it, is it a good or bad thing, what should I do? These are some of the things that different parts of the brain do in response to sounds around us. If we have a hearing loss, the brain doesn’t receive this information to sort through, many sounds are too quiet to be heard with a hearing loss, so the brain can become lazy. What happens when we don’t exercise? We become less healthy. So in a case of ‘use it or lose it’, if you have hearing loss and aren’t hearing everyday sounds the brain isn’t being exercised.

So it seems hearing aids not only help hearing but also the brain. But who wants hearing aids? We found this when recruiting people to our study – the idea of checking cognition was fine, but being advised to get hearing aids was not what many wanted to hear. People are concerned about how they appear and the cost. Hearing aid adverts tell us they are small, sophisticated, and better than ever – and that is true for the most part. Modern hearing aids are less intrusive, aesthetically pleasing, and look more elegant.

They also contain highly sophisticated, specialised processing. Our research tested different hearing aid settings and their benefits on cognition and also looked at whether more expensive hearing aids improved cognition more. Last month, I presented our results at the American Academy of Audiology annual convention – our findings were that the standard approach taken by audiologists in setting aids was better than a simple fitting. Both types of hearing aid fitting improved cognition in people with mild cognitive deficits after six months and even more after 12 months of use, but the more complex settings improved cognition more. Why? Probably because more sound was available to challenge and exercise the brain. 

As we age how much is healthy hearing and wellbeing worth? Well that’s an individual value judgment, but the benefit on cognition in our study did not depend on the cost of hearing aids. The evidence points towards the ability of the audiologist to select the most appropriate hearing aids for the job, not how expensive they are. A good argument can be made that investment in hearing aids earlier than later will not only improve prospects for healthy ageing but also, over time, reduce the health spend on dementia care. 

Hearing aids are not a cure for dementia, and not everyone with hearing aids will be protected from the effects of ageing, but they are an investment that could potentially reduce the costs of dementia care by 8 percent. We encourage the health sector to recognise hearing loss as a public health concern, to encourage awareness through public health campaigns and for governments to invest more in hearing care to reduce barriers to accessing hearing aids. Such investment should lead to costs savings as our population ages.

Given that the links between cognitive health and hearing makes scientific as well as common sense, why wouldn’t you get your ears checked, and invest in them if they need support? And the sooner, the better.

Associate Professor Grant Searchfield is based in Audiology, School of Population Health, at the University of Auckland.

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