5 questions: How might hearing loss contribute to dementia?
One theory: As hearing gets worse, you have to work harder to function in the world. That may drain cognitive energy from other tasks, contributing to impairment.
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When you get old, many people think hearing loss and cognitive decline — even dementia — are just part of the package.
But new studies suggest that the two conditions are linked, and that it might even be possible to preserve mental function by using simple tests to get ahead of hearing loss.
To learn more, we recently spoke with Thomas Willcox, associate professor and director of the Balance & Hearing Center at Thomas Jefferson University Hospital.
A recent study of 2,000 older adults by the Johns Hopkins Center on Aging and Health had some intriguing results. What were they?
The study found an independent association between cognitive decline and hearing impairment in older adults. They controlled for other factors and looked at those two variables and found that they were related, that older adults with hearing loss had an increased risk of cognitive decline, and an accelerated rate of decline over the six-year study period. It showed that older adults with hearing impairment have about a 25 percent greater risk of dementia or cognitive decline.
That's important. Our population is aging. And we know that there is a high incidence of hearing loss in older adults. The study shows that a substantial number of those are at risk of cognitive decline and dementia.
Was this just an association, or is it thought that hearing loss could contribute to or worsen dementia?
There are three prevailing theories: One is that there really is a neuro-pathological process that is shared. Your brain declines, and the same biologic process is affecting your hearing and inner ear. But that doesn't seem likely. So far, among patients with known neuropathology, we're not seeing corresponding abnormalities in the inner ear.
One of the more likely theories is associated with cognitive load. How much can your brain handle? When someone has hearing impairment, they have to cognitively work harder to function in the hearing world – to hear, to process, to understand. When we have to devote a lot of cognitive energy to this process of hearing, we may not be able to devote it to other aspects. You may not be able to keep up with your normal schedule. You're forgetful. You could say that's a temporary thing, but life is a process of hearing and interacting. Functional MRI studies have shown that people with hearing loss are reaching into other areas of their brains – outside the areas normally associated with hearing – to harness that function.
The third theory has to do with social isolation. People who are isolated and non-engaged often have manifestations of cognitive decline. It's essentially a use-it-or-lose-it phenomenon.
Among the patients I see who are severely and profoundly impaired, some are candidates for cochlear implants. Often, the family's concern is that grandmother can't hear us anymore. But then they also will not uncommonly voice concerns that grandmother isn't as sharp as she used to be. I'll see them six months later [after the procedure], and the family is talking about how grandmother blossomed and her personality came out again. She's more like they remember her to have been when she wasn't as hearing-impaired. Even the patients notice that.
Is it proven — or just hypothesized — that giving people hearing tests (and hearing aids) would prevent or slow dementia?
There is a trend in the data indicating that this might be true, but researchers didn't sample enough patients to get a statistical verification. It would take another controlled study looking at that question.
In older adults, I definitely think that a lot of people who appear to have some senility can improve with appropriate amplification. Hearing loss is an invisible disability. Patients are commonly thought to have cognitive decline, or to be aloof. I think that's a reason to want to appropriately aid people with hearing impairment.
The question is whether people who truly are on a trend of cognitive impairment are going to benefit from amplification to slow that progression, or halt that progression. That's going to take more study.
But if you're looking at incidence – one out of four hearing-impaired older adults – and if we were to find that some of them could be helped with hearing aids, that's a significant benefit. That's a lot of people.
Hearing aids seem to cause a lot of users problems. Are they improving?
Yes. They have benefited from micro-electronics. But results from hearing aids are very dependent on the people who fit patients with them, the providers. Many people think of hearing aids as products. They should be thought of as a service. There's a whole universe of amplification technology. It takes an expert to find your particular slice of that pie, and then help you choose a device, fit it to you, and tune it to your needs. And then there's the maintenance. You don't just drive your car into the ground. You get maintenance. Likewise, hearing aids aren't just a set-it and forget-it product.
What should people do to protect their hearing?
It is recommended to have your hearing checked once a decade until age 50, and then every three years or so after that. People are often surprised when they find out what their hearing test shows.
As far as prevention, you can't control your genetics. But you do control your general health. Conditions associated with age-related hearing loss include smoking, diabetes and heart disease.
The other thing you can control is hazardous noise exposure, whether it's rock concerts, celebrations, construction, etc. On walks through my neighborhood, I will not uncommonly see people using leaf blowers without protection, and I'll point to their ears. You need to be careful.