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This article originally appeared in CBC News on July 19, 2023.

Seniors at risk of dementia who were given hearing aids and counselling had less cognitive decline over a three-year period, a randomized trial finds.

Research published Monday in The Lancet medical journal found that at-risk seniors saw their rate of cognitive decline nearly cut in half over three years if they wore hearing aids, compared to seniors who just received an education.

While past research has shown a link between hearing loss and cognitive decline, experts say this study supports the need for seniors to use devices to mitigate the risk.

In Canada, audiologists estimate that around three million people have some hearing loss that could be improved with hearing aids, yet 80 per cent don’t wear them.

“It’s a testament that hearing intervention, it’s not just improving your hearing; there are a lot of cascading effects that we see now,” said the study’s co-principal investigator Dr. Frank Lin.

Lin, a professor at Johns Hopkins University’s School of Medicine and Bloomberg School of Public Health, says the study shows that good hearing “decreases loneliness, improves your social engagement, you become more active [and] it might take a load off your brain.”

The randomized control trial involved 977 participants, who were about 77 years old on average.

Some people were considered healthy, while others had underlying conditions like high blood pressure and diabetes, which put them at a greater risk for cognitive decline.

Participants were randomly divided into two groups: one that got hearing aids with additional counselling and another that only took part in a successful aging health education class.

Over three years, researchers measured the level of cognitive decline between the two groups.

There was no significant difference in cognition between the two groups overall, nor was there a notable difference for the healthy participants across both groups.

But when researchers looked at the results for just the participants who were at higher risk of dementia, those who got hearing aids slowed their cognitive decline by 48 per cent over the study period.

How is hearing tied to dementia?

According to Lin, researchers suspect that hearing loss can impact the brain in three significant ways.

The first, he said, is related to cognitive load, which means that there’s excessive work being done by the brain to compensate for poor hearing.

“Your brain is constantly getting a much more garbled signal from the ear,” he said. “And we understand now that likely takes a toll on the brain.”

The brain is constantly reallocating resources to handle hearing as a result, and that might “come at the expense” of our thinking and memory, Lin said.

A second reason is that if the brain isn’t getting enough auditory input, that can cause parts of it to shrink, said Lin.

And lastly, hearing loss can cause someone to withdraw and not be as socially engaged. This is also thought to contribute to brain atrophy.

“The thing with hearing intervention [is that] it likely targets all those pathways: it reduces load on the brain, provides more stimulation to the brain, [and] at the same time, it helps you be more engaged with your life,” said Lin

Study limits confounding factors

While these study results aren’t surprising to those in the industry, the methods used provide more robust support for the idea that hearing loss is tied to cognitive function.

There’s been a lot of research recently that shows hearing loss can be an early warning sign for potential decline, said Kathy Pichora-Fuller, a professor emeritus in psychology at the University of Toronto not involved in the study.

But what stands out to the gerontologist and audiologist is that there weren’t as many confounding factors due to the fact that participants were randomly assigned to either group.

This would mean that lifestyle factors were relatively the same between the control and intervention groups.

Typically in studies done with hearing aids, Pichora-Fuller said they compare people who have them with those who don’t.

But Pichora-Fuller says people who already own hearing aids are often different: they may be more motivated, socially engaged, wealthier or have a higher education. All of these factors could be what help preserve their mental state as they age.

“Now we can compare apples to apples,” she said about the new study.

She says it’s also important to know that the participants in this study were not only given hearing aids but also engaged in continuous audio rehabilitation with an expert.

Barriers to getting hearing aids

Even though the benefits of hearing aids have been clear for some time, those who work in the industry say patients are still reluctant to get them.

“Hearing aids do have a stigma associated with them and it’s very long-standing,” said Marilyn Reed, an audiology practice advisor at Baycrest Centre in Toronto.

“The way to overcome stigma is to really talk about the problem.”

This starts with family doctors, Reed said. Regular screening in people 50 and older in primary care, she said, can reduce shame, educate people and allow for earlier intervention.

Another barrier is cost, said Reed: The most basic hearing aids available in Canada start at around $2,000 a pair.

Most recently, the U.S. approved over-the-counter hearing aids, which has dramatically reduced the price. Many expect Canada will soon follow suit.

As for the next steps with this research, Lin says they are going to continue to follow the people who started off healthy to track if they eventually see any benefit from the hearing aids.

He says they also plan to do more research on whether there are long-term cognitive benefits with hearing aids and their ability to reduce rates of dementia.