CU Researchers Study Potential Links Between Hearing Loss and Dementia
Can hearing loss cause dementia?
ProfessorAnu Sharma gets this question a lot. As an auditory neuroscientist inCU’s Department of Speech, Language and Hearing Sciences, Sharma has spent much of her career in a soundproof room on the Boulder campus, spying on volunteers’ brain activities as headphones pipe sound into their ears. Her small yet high-tech studies have produced some of the most detailed evidence that hearing loss, even in early, mild stages, reorganizes the way the brain responds to sound and other stimuli.
The findings complement a growing body of large public health studies linking presbycusis, also known as age-related hearing loss, and cognitive decline.
A study from Johns Hopkins University found that, over the course of 12 years, people with mild hearing loss were twice as likely to be diagnosed with dementia, while those with moderate to severe hearing loss were three to five times as likely. In 2017, the Lancet Commission on Dementia Prevention identified hearing loss as the “single largest potentially modifiable risk factor for dementia.”
Such studies have sparked worrying headlines, emboldened some hearing aid companies to claim their products can “prevent Alzheimer’s disease,” and prompted older patients to ask their audiologists about cognitive health.
“Ten years ago, almost nobody would come into the clinic asking about brain health,” said Dr. Vinaya Manchaiah, director of audiology at CU Anschutz. Now, it happens all the time.
Sharma and Manchaiah still respond cautiously.
“There’s a lot of fear-mongering going on, and that worries me,” Sharma said. While ample evidence shows that hearing loss is associated with cognitive decline, it’s still not clear whether it causes it — and if so, how and what can be done.
That’s where Sharma’s lab comes in. By studying the brain activity of adults in various stages of hearing loss, she hopes to shed light not only on what, precisely, presbycusis does to the brain, but also whether hearing aids can undo the damage.
Professor Anu Sharma
Rewiring the Circuit
Seated in her office, images of brain scans glowing red and yellow on her computer monitor, Sharma explains the concept that has inspired much of her 20-year career: cross-modal plasticity.
“One of the most remarkable aspects of our brain is its ability to adapt to change,” she said. “A basic tenet of this ability is that the brain will reorganize itself following sensory deprivation.”
She first saw this in children born deaf. Sharma found that because their auditory cortex (the brain region earmarked for sound processing) was deprived of sound, their brains repurposed that valuable real estate to assist other senses, like vision and touch, instead.
This elegant rewiring has its upsides.
For instance, studies have shown that, with multiple parts of their brains weighing in to process what they see and feel, some deaf individuals are better at recognizing faces and have a heightened sense of touch.
“It is a dynamic and elegant plasticity,” said Sharma. “And for a long time we had only seen it in children that were born deaf or adults that were profoundly deaf.”
In 2011, after reading the first news stories associating hearing loss with cognitive decline, she wondered: Could such rewiring occur in earlier, milder stages of hearing loss?
She and her students recruited dozens of people with hearing loss, along with age-matched participants with normal hearing. As flashing objects marched across a monitor or vibrations tickled their fingertips, an EEG (electroencephalogram) cap with 128 electrodes measured electrical activity in their brains.
When the first results came in, “I was shocked,” recalled Sharma.
Even among those with mild hearing loss, the brain had already begun to rewire itself, leveraging parts of its sound processing center to help make sense of sights and sensations.
But of greater concern was what happened when they tried to make sense of sound.
When the repeated sound “ba” was played for those with hearing loss, it prompted only limited activation in the auditory cortex. Meanwhile, brain regions responsible for working memory and other cognitive functions crackled with activity.
“Even as early as mild hearing loss, listening becomes effortful,” Sharma explained. “As a result, you do two things: You rely more heavily on other modalities, like vision, and you use parts of your brain designed for cognition.”
Some have theorized that this extra load on the brain’s memory centers eats up “cognitive reserve,” boosting risk of decline later in life.
And Sharma’s own studies show that those with untreated age-related hearing loss tend to perform worse on cognitive tasks.
“Anu has done some landmark research showing that, even with mild hearing loss, you can have changes in the brain,” said Manchaiah. “The big question now is: Can you do something about it?”
30%
Adults over age 50 who have age-related hearing loss
15%
Adults who could benefit from hearing aids in the U.S. and use them
7-10 years
Adults typically wait this long to seek treatment for hearing loss
$2,000 to $7,000
Average cost of prescription hearing aids
$1,000 to $2,000
Average cost of OTC hearing aids
Can Hearing Aids Prevent Cognitive Decline?
In 2020, Sharma published the results of a small but groundbreaking study.
Her lab found that when 21 adults with untreated, mild to moderate age-related hearing loss wore hearing aids for six months, their brains began to look more like those of people with normal hearing again. In essence, that cross-modal plasticity had reversed.
Most also scored better on cognitive tests than they had prior to getting hearing aids.
The study, while promising, came with caveats and prompted more questions.
For instance, participants were professionally fitted with state-of-the-art hearing aids and wore them for an average of 10 hours a day. Would people experience beneficial brain changes and cognitive improvements with less expensive hearing aids? How much does fit matter? And how long do they need to be worn?
Larger studies elsewhere have yielded mixed results.
One randomized controlled trial, published in 2023, showed that hearing aids did not reduce the risk of cognitive decline on a population-wide level, but they did in specific subgroups, including people with cardiovascular disease.
All this makes it hard for doctors to give patients a straight answer, said Manchaiah.
So, he and Sharma are working to fill the research gap.
In 2025, armed with a $3.5 million National Institutes of Health grant, they launched an ambitious five-year study.
The randomized controlled trial plans to recruit 280 people with early, untreated hearing loss and divide them into four groups: prescription hearing aids with professional fit; over-the-counter (OTC) hearing aids with in-person support from an audiologist; OTC hearing aids with online support from an audiologist; and OTC self-fit groups.
All study participants will receive free hearing aids (to keep) and undergo EEG, cognitive and behavioral testing before and after use. They will complete questionnaires and surveys throughout the study.
“This is one of the largest hearing aid studies ever done, in terms of the number of different things we are measuring,” said Machaiah, who is leading the study along with Sharma. “There are many unanswered questions, but in a few years we will have a lot more answers.”
In the meantime, Sharma said there are many other reasons to seek treatment for age-related hearing loss, as research has shown it can contribute to social isolation and depression.
“Regardless of the cognitive issues, if you have hearing loss, it’s really smart to get hearing aids,” said Sharma. “They will enhance your quality of life.”
To inquire about participating in the study, emaileeglab@colorado.edu.
Illustrations by Petre Péterffy
