It really doesn't seem fair: Hearing loss, a troublesome fact of life for more than 48 million Americans, according to the Hearing Loss Association of America, may increase the risk of cognitive problems and even dementia. By the time Americans reach their 70s, two-thirds have hearing loss.
"The general perception is that hearing loss is a relatively inconsequential part of aging," says Frank Lin, an otologist and epidemiologist at Johns Hopkins University in Baltimore. But recent findings, he says, suggest that it may play a much more important role in brain health than we've previously thought.
Fortunately, there's a potential upside. If this connection — shown in several recent and well-regarded studies — holds up, it raises the possibility that treating hearing loss more aggressively could help stave off cognitive decline and dementia. Lin and other researchers have several theories about the possible explanation for the link between hearing and dementia, although they aren't yet sure which of them — if any — will prove true.
Lin is the author of several recent studies pointing to a link between hearing and cognitive problems ranging from mild impairment all the way to dementia.
In a 2013 study, he and his colleagues tracked the overall cognitive abilities (including concentration, memory and planning skills) of nearly 2,000 older adults whose average age was 77. After six years, those who began the study with hearing loss severe enough to interfere with conversation were 24 percent more likely than those with normal hearing to see their cognitive abilities diminish. Essentially, the researchers said, hearing loss seemed to speed up age-related cognitive decline.
In a 2011 study focusing on dementia, Lin and his colleagues monitored the cognitive health of 639 people who were mentally sharp when the study began. The researchers tested the volunteers' mental abilities regularly, following most for about 12 years, and some for as long as 18 years. The results were striking: The worse the initial hearing loss was, the more likely the person was to develop dementia. Compared with people of normal hearing, those with moderate hearing loss had triple the risk.
Lin is quick to point out that simply being at increased risk does not mean a person is certain to develop dementia.
"I have a 92-year-old grandmother who's had a moderately severe hearing loss for many years now," Lin says. "She's sharp as a tack. I was talking to her about my research and she looks at me and says, 'Are you telling me I'm definitely going to get dementia?' "
"I said, 'Not by any means.' "
A recent study, led by Isabelle Mosnier of Assistance Publique-Hopitaux de Paris in France, offers more hope. Mosnier studied a group of 94 people ages 65 to 85 with profound deafness in at least one ear. Each received a cochlear implant followed by twice-weekly auditory rehabilitation. More than 80 percent of those with the lowest cognitive scores showed significant improvement one year after implantation, according to the study published March 12 in the journal JAMA Otolaryngology-Head & Neck Surgery.
P. Murali Doraiswamy, M.D., a professor of psychiatry and medicine at Duke University School of Medicine and coauthor of The Alzheimer's Action Plan, says that although the study had some shortcomings, "the improvement in cognition was huge — about double that seen with any of the current [U.S. Food and Drug Administration] FDA drugs for treating Alzheimer's." He adds that the findings about hearing loss affecting cognitive tests probably also apply to other senses such as vision, smell and touch. "Studies have shown that uncorrected vision problems raise the risk for dementia," he says.
While the link between hearing loss and milder cognitive problems has been questioned by some, it is becoming increasingly accepted. "Every doctor knows that hearing loss can result in cognitive problems, but they still don't focus on it as a priority when they evaluate someone with suspected dementia — which is a big missed opportunity," Doraiswamy says. "The benefits of correcting hearing loss on cognition are twice as large as the benefits from any cognitive-enhancing drugs now on the market. It should be the first thing we focus on."
Still, he adds, "We need long-term controlled trials looking at whether cochlear implants can delay the onset of dementia in at-risk subjects, which will clinch the case."