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Hearing loss is now known to be an often-preventable risk factor for dementia, and research is building the case for hearing aids as one of the stronger tools to protect against it.
A new study this month on older adults with untreated hearing loss, published in The Lancet, found that wearing hearing aids produced a noteworthy decrease of dementia -- nearly 50% -- over a three-year period among those who were already at higher risk for cognitive decline (cognitive decline describes problems with mental action and processing, like thinking, remembering and communicating).
The study compared how well hearing hearing aids and audiological counseling compared to educating people in the study (adults in their 70s and 80s) about preventing chronic disease, which can also be a risk factor for dementia. While hearing aids didn't reduce the risk of dementia in people who weren't at high risk in the first place, wearing hearing aids over the study period did slash the risk among people who had a higher likelihood of cognitive decline in the first place.
While more longer-term information is needed on the use of hearing aids in people at lower risk of dementia, the newer study found, it is the latest evidence attempting to bridge the link between hearing loss and dementia. One study from Johns Hopkins, for example, followed over 600 adults for 12 years and found that mild hearing loss doubled the risk of dementia. Moderate hearing loss tripled someone's risk of dementia, and severe hearing loss increased the risk by five times.
For the millions of adults with hearing loss, and the estimated 150 million in the world who will be affected by dementia by 2050, further untangling the link between hearing loss and dementia is imperative. Here's what we know now.
Dementia is a general term for a person's inability to think, communicate and remember things clearly, affecting their mood, personality and behavior. There are different causes, but the most common disease that leads to dementia is Alzheimer's. The risk of dementia increases with age, as does the risk of hearing loss.
About one-third of older adults have hearing loss, so when hearing aids became available over the counter last fall, many experts in medicine and public health celebrated. Not only are OTC hearing aids typically cheaper, but fewer appointments and easier access will hopefully mean more people will maintain oral language, a bridge for communication and cognition.
"Language and cognition are two distinct processes, but they are highly interdependent," Brooke Hatfield, associate director of health care services in speech-language pathology at the American Speech-Language-Hearing Association, said in an email. "Language serves as an internal framework for reasoning, problem solving, memory and other thinking skills."
According to the Cochlear Center for Hearing and Public Health, a branch of the Johns Hopkins Bloomberg School of Public Health, hearing loss accounts for the greatest number of "potentially preventable" cases of dementia. This is compared to other factors that may influence dementia risk, such as high blood pressure and lower education.
Researchers think hearing loss has this effect because of how it stops sound from entering the brain. If someone is struggling to hear, their brain will have to stress to understand sound, potentially speeding up the aging process in the brain and limiting how a person is able to think and remember things, according to a fact sheet from the Cochlear Center.
Losing the ability to hear the people around you also limits your communication and connection with them, which may lead to social isolation – an existing public health problem among seniors and older adults. Social isolation was found to be associated with a rough 50% increased risk of dementia and other health problems, according to the US Centers for Disease Control and Prevention.
Put together, the different theories on hearing loss and dementia may also be a "chicken or the egg" scenario, according to Hatfield. She pointed to research that found hearing loss is a marker for changes in the brain that are already underway, as opposed to the changes coming from hearing loss.
Not everyone who has hearing loss developed it over time, however, and the risk of dementia doesn't appear to be the same in people with lifelong deafness. For people born deaf who use sign language to communicate, there does not appear to be an increased risk of dementia compared to the general population, according to the UK-based charity Social Care Institute for Excellence.
But Hatfield adds there's some concern over diagnosing dementia in patients who are deaf, due to the limits of tests as well as a lack of provider experience in working with people in the deaf community. But there still may be a "protective factor" of staying engaged with communication and avoiding social isolation when it comes to dementia risk.
"The tie to dementia and hearing loss appears to be related to having a history of hearing that changes and so the brain changes in response, rather than being related to the act of hearing itself," Hatfield added.
Given what we know about hearing loss and cognitive ability, it makes sense that the number one way to preserve hearing loss -- wearing hearing aids -- may play an important role. The Lancet study from this month, centered on older adults with untreated hearing loss, seems to confirm the power of the hearing aid in preserving cognition. At least, reducing the risk of cognitive decline by correcting hearing loss in people who are already at a higher risk of cognitive decline.
This is in addition to a study published this spring in The Lancet found that people with hearing loss who also use hearing aids did not have an increased risk of dementia compared to people without hearing loss. Researchers in the study used data from the UK Biobank to look at the health records and dementia diagnoses of a large cohort of adults ages 40 to 69 from England, Scotland and Wales.
If "causality" is established through more research, authors in the study wrote, hearing aids will "present a minimally invasive, cost-effective intervention to mitigate all or at least some of the effect of hearing loss on dementia."
A large systematic review from February also added evidence that hearing aids for people that need them may help stave off risk of cognitive decline. The review looked at studies on the use of hearing aids in people with hearing loss, finding that the use of "hearing restorative devices" was associated with a 19% decrease in hazards of long-term cognitive decline.
Even with the promising research on hearing aids and cognition, hearing aids won't be a quick fix for dementia that's already set in. But starting to wear them early, when someone notices hearing loss, may help people at higher risk reduce their chances of dementia as well as the other frustrating consequences of hearing loss.
The average time someone waits to get hearing loss treatment -- which is a hearing aid, in many cases -- is seven to nine years. But similar to other medical conditions, the earlier someone with hearing loss seeks treatment, the better their outcome will be, according to Bria Collins, associate director of audiology practices at ASHA.
"The longer someone who communicates through spoken language waits to seek treatment, the more difficult it may be to adjust to hearing speech and environmental sounds again," Collins said in an email. Think of hearing and language as a muscle we need to exercise, like a runner who ticks off several miles each week, she explains. If a runner took a years-long break from exercise, she "would not be at the level of athletic performance she was at when her muscles/endurance were accustomed to exercise."
How long it takes someone to get their language or performance back after getting a hearing aid varies, Collins says. For example, there's evidence that the brain adjusts to having a hearing aid after about four weeks. And while many people feel relief from "listening fatigue" almost immediately in situations where they're watching TV or having a one-on-one conversation, they typically will need more time to adjust to more "challenging" listening environments that require more discernment, like restaurants, bars or a busy family gathering.
It also depends on how long someone has been without hearing and the severity of their hearing loss – going from having a very hard time hearing to being thrown into a world full of sound may be jarring for some patients. This is why audiologists may adjust hearing aids gradually over time for patients, Collins explains, so patients are not overwhelmed. (This is one noted con for over-the-counter hearing aids and how they may fall short compared to prescription hearing aids that are fitted by a professional.)
"In short, there is not one specific time period it takes the brain to adjust to amplification," she said. "There is a lot of individual variability."
The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.