I’M SO SORRY, COULD YOU REPEAT THAT PLEASE?

by Women’s Brain Health Initiative:

The Impact of Hearing Loss on Cognitive Health

For so many of us, hearing loss is considered a normal part of the aging process and no great cause for alarm. But studies from Johns Hopkins University have found links between hearing loss, cognitive decline and dementia.  

"Hearing loss shouldn't be considered an inconsequential part of aging," said Dr. Frank Lin, assistant professor at Johns Hopkins and an otologist and epidemiologist who studies the effects of hearing loss on older adults. In one study involving nearly 2,000 men and women age 75-84, Lin and his colleagues found that over six years, cognitive abilities (including memory and concentration) of those with hearing loss declined 30 to 40 percent faster than in people with normal hearing.

A 2011 study of some 600 older adults found that those with hearing loss at the beginning of the study were more likely to develop dementia than adults with normal hearing. In fact, the more severe the hearing loss, the more likely they were to develop dementia; volunteers with mild, moderate and severe loss were two, three and five times more likely to develop dementia than those with normal hearing.

Another study by Lin and his colleagues found accelerated rates of brain atrophy in people with impaired hearing compared with those who had normal hearing.  In addition, they linked hearing loss to "deep episodes of stress, depression or bad mood," an increased risk of hospitalization and an increase in the risk of falls.

Dr. Richard Gurgel, assistant professor of otolaryngology-head and neck surgery at University of Utah Health Care, studied more than 4,400 men and women 65 and older; those with hearing loss at the beginning of the study developed dementia at a higher rate and earlier than those without hearing loss. Gurgel, Lin and others are now focused on finding out whether hearing loss causes dementia or is related to dementia. "Dementia has so many causes. I think hearing loss could be a very important component, but there are certainly a lot of factors that play into dementia," Gurgel said.

The first theory is "cognitive load." If the brain is constantly coping with degraded sounds, its resources are dedicated to processing those sounds, to the detriment of other processes like memory and thinking. The second theory involves brain atrophy. Hearing impairment may directly contribute to accelerated rates of atrophy in parts of the brain that process sound. Those parts of the brain don't work in isolation, according to Lin; they "also play roles in memory and sensory integration and have been shown to be involved in the early stages of mild cognitive impairment and Alzheimer's disease."

The third explanation is social isolation. People who have a hard time hearing often withdraw because it's so difficult to communicate with others. Numerous studies have found that a loss of engagement and loneliness are risk factors for cognitive decline.

Though estimates on hearing loss vary, the National Institute on Deafness and Other Communication Disorders estimates that nearly 25 percent of those age 65 through 74 and 50 percent of those 75 and older have disabling hearing loss. About 26 million Americans age 20 to 69 have high-frequency hearing loss due to noise exposure.

And though millions could benefit from hearing aids, few of us use them; among adults 70 and older with hearing loss who could benefit from hearing aids, fewer than one in three (30 percent) use them. Even fewer adults age 20 to 69 (about 16 percent) who could benefit from hearing aids use them. 

A study published in October 2015 is the first to show that wearing hearing aids reduces cognitive decline associated with hearing loss. This was a 25-year study that followed 3,670 adults, age 65 and older. The study included three groups of subjects: those who did not report hearing loss (considered the control group); those with hearing loss who did not use hearing aids, and those with hearing loss who did use hearing aids.

The researchers compared the rate of cognitive decline among these groups and found no difference between the control group and those who used hearing aids, but did find those with untreated hearing loss had lower scores on a test of cognitive function.

Lin and his team now plan a study that they hope will answer the "million-dollar question": Does treating hearing loss reduce the risk of dementia? The five-year study will follow 800 older adults and measure cognitive decline; some will get state-of-the-art hearing treatment while others will simply get "wellness advice." Gurgel and colleagues are also looking at whether treating someone's hearing loss will improve cognition.

"If we treat hearing loss, how much difference will it make? I can tell you in a few years when we complete this trial," Lin said. "If we look at risk factors for cognitive decline that are modifiable, and hearing loss is one of them, that could be tremendously exciting. (Hearing loss) is really common, and theoretically the treatments we have are no risk. That makes it very exciting as a public health target."

According to Rex Banks, Doctor of Audiology at the Canadian Hearing Society,

“All signs and research are pointing towards hearing aids being a treatment for dementia but we are just not there yet to say that this is definitively true.  Research is ongoing in this area.”