A Strain to Hear And a Loss of Memory ; Researcher Examines a Link between Auditory Deficit And Dementia
International Herald Tribune
Frank Lin, an otolaryngologist at Johns Hopkins School of Medicine, has been exploring the strong association he has found between hearing loss and dementia.
At a party the other night, a fund-raiser for a literary magazine, I found myself in conversation with a well-known author whose work I greatly admire. I use the term "conversation" loosely. I couldn't hear a word he said. But worse, the effort I was making to hear was using up so much brain power that I completely forgot the titles of his books.
A senior moment? Maybe. (I'm 65.) But for me, it's complicated by the fact that I have severe hearing loss, only somewhat eased by a hearing aid and cochlear implant.
Frank Lin, an otolaryngologist and epidemiologist at Johns Hopkins School of Medicine, describes this phenomenon as "cognitive load." Cognitive overload is the way it feels. Essentially, the brain is so preoccupied with translating the sounds into words that it seems to have no processing power left over to search through the storerooms of memory for a response.
Over the past few years, Dr. Lin has delivered unwelcome news to those of us with hearing loss. His work looks "at the interface of hearing loss, gerontology and public health," as he writes on his Web site. The most significant issue at this juncture is the relationship between hearing loss and dementia.
In a 2011 paper in Archives of Neurology, Dr. Lin and colleagues found a strong association between the two. The researchers looked at 639 subjects, ranging in age at the beginning of the study from 36 to 90 (with the majority between 60 and 80), The subjects were part of the Baltimore Longitudinal Study of Aging. None had cognitive impairment at the beginning of the study, which followed subjects for 18 years; some had hearing loss.
"Compared to individuals with normal hearing, those individuals with a mild, moderate and severe hearing loss, respectively, had a 2- , 3- and 5- fold increased risk of developing dementia over the course of the study," Dr. Lin wrote in an e-mail summarizing the results. The worse the hearing loss, the greater the risk of developing the dementia. The correlation remained true even when age, diabetes and hypertension -- other conditions associated with dementia -- were ruled out.
In an interview, Dr. Lin and I discussed some possible explanations for the association. The first is the social isolation that comes with hearing loss; isolation is a known risk factor for dementia. Another possibility is cognitive overload, and a third is some pathological process that causes both hearing loss and dementia.
In a study published last month, Dr. Lin and colleagues looked at 1,984 older adults beginning in 1997-8, again using a well- established database. Their findings reinforced those of the 2011 study but also found that those with hearing loss had a "30 to 40 percent faster rate of loss of thinking and memory abilities" over a six-year period compared to people with normal hearing. Again, the worse the hearing loss, the worse the rate of cognitive decline.
Both studies also found that hearing aids were "not significantly associated with lower risk" for cognitive impairment. But self- reporting of hearing-aid use is unreliable, and Dr. Lin's next study will focus specifically on the way hearing aids are used: for how long, how frequently, how well they've been fitted, what kind of counseling the user received, what other technologies they used to supplement hearing-aid use.
What about the notion of a common pathological process? In a paper in the journal Neurology, John Gallacher and colleagues at Cardiff University suggested the possibility of a genetic or environmental factor that could be causing both hearing loss and dementia -- and perhaps not in that order. In a phenomenon called reverse causation, a degenerative pathology that leads to early dementia might prove to be a cause of hearing loss.
The work of John T. Cacioppo, director of the Social Neuroscience Laboratory at the University of Chicago, also offers a clue to a pathological link. His multidisciplinary studies on isolation have shown that perceived isolation, or loneliness, is "a more important predictor of a variety of adverse health outcomes than is objective social isolation." Those with hearing loss, who may sit through a dinner party and not hear a word, frequently experience perceived isolation.
Other research, including the Framingham Heart Study, has found an association between hearing loss and another unexpected condition: cardiovascular disease. Again, the evidence suggests a common pathological cause. David R. Friedland, a professor of otolaryngology at the Medical College of Wisconsin in Madison, hypothesized in a 2009 paper delivered at a conference that low- frequency loss could be an early indication that a patient has vascular problems: the inner ear is "so sensitive to blood flow" that any vascular abnormalities "could be noted earlier here than in other parts of the body."
A common pathological cause might help explain why hearing aids do not seem to reduce the risk of dementia. But those of us with hearing loss hope that is not the case; common sense suggests that if you don't have to work so hard to hear, you have greater cognitive power to listen and understand -- and remember. And the sense of perceived isolation, another risk for dementia, is reduced.
A critical factor may be the way hearing aids are used, the subject of Dr. Lin's next study. Hearing aids require practice to work properly, and frequent reprogramming by an audiologist. Additional assistive technologies like looping and FM systems may also be required. People with progressive hearing loss may need new hearing aids every few years.
Hearing aids are increasingly bought online or from big-box stores, making it hard for the user to follow up. In the first year I had hearing aids, I saw my audiologist initially every two weeks for reprocessing and then every three months.
Whether they are using their hearing aids correctly or not, hearing aid users are in the minority. In another study, Dr. Lin and his colleague Wade Chien found that only one in seven adults who could benefit from hearing aids used them. One deterrent is cost ($2,000 to $6,000 an ear, seldom covered by insurance). Another is the stigma of old age.
Hearing loss is a natural part of aging. But for most people with hearing loss, according to the National Institute on Deafness and Other Communication Disorders, the condition began long before they got old. Almost two-thirds of men with hearing loss began to lose their hearing before age 44. My hearing loss began when I was 30.
Forty-eight million Americans alone suffer from some degree of hearing loss. If it can be proved in a clinical trial that hearing aids help delay or offset dementia, the benefits would be immeasurable. Dr. Lin speaks passionately about the need for this research.
"Could we do something to reduce cognitive decline and delay the onset of dementia?" he asked. "It's hugely important, because by 2050, 1 in 30 Americans will have dementia.
"If we could delay the onset by even one year, the prevalence of dementia drops by 15 percent down the road. You're talking about billions of dollars in health care savings."
Should studies establish definitively that correcting hearing loss decreases the potential for early-onset dementia, we might finally overcome the stigma of hearing loss. Get your hearing tested, get it corrected, and enjoy a longer cognitively active life. Establishing the dangers of uncorrected hearing might even persuade private insurers and Medicare that covering the cost of hearing aids is a small price to pay to offset the cost of dementia.