"The general perception is that hearing loss is a relatively inconsequential part of aging," says Frank Lin, M.D., an otologist and epidemiologist at Johns Hopkins University. 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 cause of the link between hearing and dementia, although they aren't yet sure which of them — if any — will hold 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 have seen their cognitive abilities diminish. Essentially, the researchers say, 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, 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 [90-year-old] grandmother who's had a moderately severe [hearing] loss for many years now," says Lin. "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.' "
What's more, while the link between hearing loss and milder cognitive problems is becoming increasingly accepted, some researchers aren't convinced that hearing loss raises a person's chances of developing dementia.
"Everyone in the field agrees that hearing loss is a risk for cognitive problems," says P. Murali Doraiswamy, M.D., a professor of psychiatry at Duke University and author of The Alzheimer's Action Plan. "But I don't think the field takes mild hearing loss as a cause of Alzheimer's seriously yet." Nor, he says, do most researchers agree that hearing loss is related to other common types of dementia.
Still, he adds, "There are plausible reasons for why hearing loss might lead to dementia — the brain's hearing centers are very close to the regions where Alzheimer's first starts."