Hearing Loss Linked to Cognitive Decline, Impairment

Pauline Anderson

January 23, 2013

Older adults with hearing loss have a rate of cognitive decline that is up to 40% faster than the rate in those with normal hearing, according to results of a new study. Those with hearing loss also appear to have a greater risk for cognitive impairment.

"I would argue going forward for next 30 or 40 years that from a public health perspective, there's nothing more important than cognitive decline and dementia as the population ages," said lead author Frank R. Lin, MD, PhD, assistant professor, otolaryngology, geriatrics, and epidemiology, Johns Hopkins University, Baltimore, Maryland.

"So from a big picture point of view, identifying factors that are associated with cognitive decline and dementia are important, in particular those factors that are potentially modifiable."

Although the study did not find a significant association between hearing aid use and rate of cognitive decline, Dr. Lin is convinced that addressing hearing loss could have an impact greater than just improving quality of life.

The study was published online January 21 in JAMA Internal Medicine, formerly known as Archives of Internal Medicine.

Hearing Loss Definition

The analysis included 1984 participants in the Health ABC (Health, Aging, and Body Composition) study, a prospective observational investigation of well-functioning community dwelling adults aged 70 to 79 years, who had no evidence of cognitive impairment, defined as a Modified Mini-Mental State Examination (3MS) score of 80 or higher, and who underwent audiometric testing.

Hearing loss was defined as a speech frequency pure-tone average of hearing thresholds at 0.5, 1, 2, and 4 kHz in the better hearing ear exceeding 25 decibels. This is the level at which hearing loss begins to impair daily communication and has been adopted as the definition of hearing loss by the World Health Organization.

The study used both the Digit Symbol Substitution (DSS), a nonverbal test of psychomotor speed and executive function, and the 3MS, a verbal test with components for orientation, concentration, language, praxis, and memory. Cognitive impairment was defined as a 3MS score of less than 80 or a decline in 3MS of more than 5 points from baseline.

After adjustment for demographic characteristics and cardiovascular risk factors, participants with hearing loss had cognitive scores at baseline that were on average –0.75 (95% confidence interval [CI], –1.17 to –0.33) points lower on the 3MS and –0.92 (95% CI, –1.94 to 0.10) points lower on the DSS than those with normal hearing.

Participants with hearing loss had annual rates of decline on the 3MS that were 41% greater than rates among participants with normal hearing. On average, those with hearing loss had adjusted 3MS scores that declined from 90.3 (95% CI, 89.9 - 90.8) at baseline to 86.4 (95% CI, 85.7 - 87.1) at the end of the follow-up period compared with 91.0 (95% CI, 90.5 - 91.6) at baseline and 88.3 (95% CI, 87.5 - 89.1) at follow-up for those with normal hearing.

On the DSS, participants with hearing loss had annual rates of decline that were 32% greater than those among participants with normal hearing. On average, participants with hearing loss had DSS scores of 31.1 (95% CI, 29.9 - 32.3) at baseline and 26.1 (95% CI, 24.8 - 27.4) at follow-up compared with 32.0 (95% CI, 30.7 - 33.4) at baseline and 28.3 (95% CI, 26.9 - 29.6) at follow-up for those with normal hearing.

Restricting the analysis to participants without severe hearing loss or to those who remained dementia free did not substantially affect the results. Scores on the Center for Epidemiological Studies Depression Scale did not substantially change the magnitude of the association between hearing loss and accelerated cognitive decline.

During follow-up, there were 609 cases of incident cognitive impairment. Participants with hearing loss at baseline had a significant 24% increased risk for incident cognitive impairment compared with those having normal hearing (hazard ratio, 1.24; 95% CI, 1.05 - 1.48; P = .01).

Hearing Aid Use

Although hearing aid use was not significantly associated with lower risk for incident cognitive impairment, the study may have been underpowered to detect a significant association. "The overall direction suggested that there could possibly be a protective association" between hearing aid use and cognition, said Dr. Lin.

"In a study like this, it's really hard to parse out whether that's true or not, mainly because there are lot of differences between people who choose to get a hearing aid versus those who don't. For example, those who do get aids may be more likely to be socially engaged to begin with or are more likely to be health conscious, so it's really hard to read into that data at this point."

However, on the basis of his "clinical intuition" and observations of his own family members, he believes technology that allows older adults to communicate more effectively "is a bit of a game changer in terms of how well they engage in their life," said Dr. Lin. "My gut feeling is that it could make a difference, but how big a difference, I don't know. The good news is that there's no down side to it."

Although the study could not determine the mechanism driving the association between hearing loss and cognitive decline, it's possible that the 2 phenomena have an as yet unidentified shared neuropathologic origin. Another explanation is that hearing loss leads to communication difficulties that result in social isolation, which has been linked to cognitive decline and dementia.

"Cognitive Load"

Yet another possible explanation is "cognitive load," the idea that as hearing loss occurs, greater resources are dedicated to auditory processing to the detriment of other cognitive processes. "If your inner ears are no longer able to encode sounds very accurately and you're constantly getting garbled messages or constantly having to expend more resources to help with hearing, that probably comes at the expense of systems such as thinking and memory and cognition," said Dr. Lin.

He believes that the mechanism is probably a combination of causes. "It's not that one explanation is right and the others are wrong; these are not mutually exclusive pathways. For any given person, it's probably a combination of all 3 mechanisms having an effect."

The study goes a long way toward changing the perception that hearing loss is a common but not that serious aspect of aging, and Dr. Lin believes physicians can play a role in broadening that message. "Hearing loss is not just an inconsequential part of aging but something that we probably need to address," he said.

He stressed that hearing loss is "complex," and addressing the problem requires not just supplying a patient a hearing aid but also comprehensive counseling and rehabilitation.

According to the authors, hearing loss is prevalent in almost two thirds of adults older than 70 years.

Dual Sensory Impairment

Hearing loss combined with vision loss — or dual sensory impairment (DSI) — occurs in 11.3% of all adults 80 years of age or older, according to another study to which Dr. Lin contributed, outlined in a research letter also published online January 21 in JAMA Internal Medicine.

This estimate, derived from data from the 1999 to 2006 cycles of the National Health and Nutritional Examination Survey (NHANES), a nationally representative sample of noninstitutionalized US residents, is substantially higher than previous estimates.

The effect of DSI on cognition is inadequately understood, and there is little research on how to effectively treat or rehabilitate older adults with these problems, the authors write.

A collaborative research approach is urgently needed to investigate the effect of DSI, as well as to examine possible treatment and rehabilitative strategies in older adults, said Dr. Lin.

"We can no longer take a piecemeal approach to medicine where I do my thing and you do your thing and the patient will come out better because of it," he said. "There's no doubt that increasingly there needs to be more coordination of the care between geriatricians and otologists or audiologists and ophthalmologists."

In a separate "Editor's Note" column published simultaneously online, Patrick G. O'Malley MD, points out that "we cannot afford to neglect" multiple sensory deficits because they will probably become a sufficient population burden as the number of elderly patients grows.

"Although there is insufficient evidence to recommend screening for both hearing loss and vision loss, efficacious treatments exist for both and physicians should be attentive to signs of either impairment," Dr. O'Malley concludes.

Asked to comment on Dr. Lin's study of hearing loss, Jonathan Peelle, PhD, assistant professor of otolaryngology, Washington University, St. Louis, Missouri, said the results are "convincing" and "a step in the right direction."

Dr. Peelle noted that although the magnitude of cognitive decline predicted by hearing loss was statistically significant, it is not enormous. "It's not that everyone with hearing loss is suddenly developing dementia, but that poorer hearing appears to exert some additional influence on cognitive ability. That being said, over the course of years or decades, this effect could well be noticeable."

Challenges for future research will be to determine the mechanism linking hearing loss and cognitive ability and to identify interventions that could slow cognitive decline related to hearing loss, said Dr. Peelle.

"As noted by the authors, research suggests that when listening is more challenging our brains must work harder to understand what has been said," he concludes. "It could be that this increased cognitive demand has long-term consequences for brain health. Alternatively, it might also be that decreasing sensory input to the brain deprives it of auditory information, which may similarly be reflected in long-term changes in brain function."

Dr. Lin reports being a consultant to Pfizer and an unpaid speaker for Cochlear Europe, a cochlear implant manufacturer. Dr. Peelle has disclosed no relevant financial relationships.

JAMA Intern Med. Published online January 21, 2013. Abstract  Research Letter  Editor's Note

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