A new study by researchers at Johns Hopkins has found an apparent link between hearing loss and accelerated cognitive decline in older adults. The new study was published on January 21, 2013 in JAMA Internal Medicine, a journal of the American Medical Association.
The study, conducted by Frank R. Lin, M.D., Ph.D., Assistant Professor of Otolaryngology, Geriatrics, and Epidemiology at Johns Hopkins University, Baltimore, and colleagues, found that among 1,984 older adults, aged 70 to 79, those with hearing loss at the beginning of the study suffered a rate of cognitive decline up to 41% faster than the rate experienced by those with normal hearing, over a six-year study period.
In addition, those with hearing loss had a 24% greater risk of experiencing cognitive decline to the point of reaching “cognitive impairment” during the six-year study period.
“I would argue going forward for [the] 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,” Dr. Lin, the lead author, told Medscape Today.
In background to their study, the authors wrote that the prevalence of dementia is projected to double every 20 years going forward, because of the aging of the world’s population.
“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,” Dr. Lin said.
The Study; Methodology
The Johns Hopkins researchers analyzed data on 1,984 older adults (average age about 77 years) who were enrolled in the Health ABC Study, a large, prospective observational study begun in 1997-1998.
None of the participants had cognitive impairment at the beginning of the study (meaning they all had a Modified Mini-Mental State Examination (3MS) score of 80 or greater at the beginning of the study).
The participants underwent audiometric testing, to measure their hearing, at the beginning of the study and in year 5 of the study. “Participants were followed up for 6 years,” the authors report. According to the authors, “Hearing was defined at baseline using a pure-tone average of thresholds at 0.5 to 4 kHz in the better-hearing ear.”
The participants underwent cognitive testing at the beginning of the study and in years 5, 8, 10, and 11, consisting of the Modified Mini-Mental State Examination (3MS), measuring global function, and the Digit Symbol Substitution test, measuring executive function.
“Cognitive impairment was defined as a 3MS score of less than 80 or a decline in 3MS score of more than 5 points from baseline,” the authors explain.
The authors used statistical analysis, adjusting for demographic and cardiovascular risk factors, to determine the extent of association between hearing loss and rate of cognitive decline over a six-year study period. They also measured the association between hearing loss and risk of developing actual cognitive impairment over the study period. In addition, they reported attempting, inconclusively, to measure any relationship between wearing a hearing aid and extent of cognitive decline.
The researchers found that a total of 1,162 individuals who had hearing loss at the beginning of the study (a pure-tone average >25 dB) had annual rates of cognitive decline 41% greater than those with normal hearing, as measured by their Modified Mini-Mental State Examination (3MS) scores (measuring global function). Those with hearing loss had rates of cognitive decline 32% greater than those with normal hearing on the Digit Symbol Substitution test (measuring executive function).
In addition, the individuals with hearing loss at the beginning of the study had a 24% greater risk than those with normal hearing, of declining to the point of developing actual cognitive impairment (“a 3MS score of less than 80 or a decline in 3MS score of more than 5 points from baseline”), according to the study results.
“Rates of cognitive decline and the risk for incident cognitive impairment were linearly associated with the severity of an individual’s baseline hearing loss,” the researchers reported.
The researchers, however, did not find any statistically significant association between use of a hearing aid and rate of cognitive decline or risk of cognitive impairment.
Hearing Loss Correlates with Faster Cognitive Decline and Greater Risk of Cognitive Impairment
“Our results demonstrate that hearing loss is independently associated with accelerated cognitive decline and incident cognitive impairment in community-dwelling older adults,” the authors wrote.
“The magnitude of these associations is clinically significant, with individuals having hearing loss demonstrating a 30 percent to 40 percent accelerated rate of cognitive decline and a 24 percent increased risk for incident cognitive impairment during a six-year period compared with individuals having normal hearing.”
The authors reported that, on average, individuals with hearing loss declined mentally by 5 points (a level of decline indicating cognitive impairment) on the 3MS test over a period of 7.7 years, while those with normal hearing on average took 10.9 years to decline by 5 points.
“In conclusion, our results suggest that hearing loss is associated with accelerated cognitive decline and incident cognitive impairment in older adults,” the authors wrote.
What Mechanisms Explain the Association between Hearing Loss & Cognitive Decline?
The study was not able to determine what specific mechanism(s) may underlie the association between hearing loss and cognitive decline. “Further research is needed to investigate what the mechanistic basis of this observed association is and whether such pathways would be amendable to hearing rehabilitative interventions,” the authors wrote.
In an interview with Medscape Today, however, lead author Dr. Lin posited three potential mechanisms that may help explain the relationship:
- It may be possible that the 2 phenomena — hearing loss and cognitive decline — have an “as yet unidentified shared neuropathologic origin;” or
- Perhaps “hearing loss leads to communication difficulties that result in social isolation, which has been linked to cognitive decline and dementia;” or
- The concept of “Cognitive Load” may be at work. Under this theory, as hearing loss occurs, greater mental resources may be required and dedicated to processing auditory signals, which deprives other cognitive processes of those mental resources. “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,” Dr. Lin explained.
Dr. Lin told Medscape Today that he believes the explanatory 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,” he said.
Can Wearing a Hearing Aid Help Stave Off Mental Decline?
While the study did not find a statistically significant relationship between wearing a hearing aid and rate of mental decline or risk of cognitive impairment, Dr. Lin, the principal study author, explained to Medscape Today that it was difficult accurately to measure whether use of a hearing aid alone may have helped stave off mental decline. This was so, he said, “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, Dr. Lin told Medscape Today that, 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.” “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,” Dr. Lin said.
According to Dr. Lin, an important significance of the new study may be that it “goes a long way toward changing the perception that hearing loss is a common but not that serious aspect of aging.” He called upon physicians to play a role in communicating that message. “Hearing loss is not just an inconsequential part of aging but something that we probably need to address,” Dr. Lin said.
He stressed that hearing loss is “complex,” and that “addressing the problem requires not just supplying a patient a hearing aid but also comprehensive counseling and rehabilitation.”
According to the study authors, hearing loss is prevalent in almost two thirds of adults older than 70 years.
In a related research letter, also published in the January 21, 2013 issue of JAMA Internal Medicine, researchers reported that, based on an analysis of data from the 1999-2006 cycles of the National Health and Nutritional Examination Surveys (NHANES), a large, ongoing prospective health study, they estimated that approximately 1.5 million Americans 20 years or older had dual sensory impairment (DSI) in hearing and vision loss, with nearly all the affected individuals being older adults.
This number is much larger than had been previously estimated, based on studies that involved only self-reporting and less scientific measures.
For individuals younger than 70 years old, the new analysis found that prevalence of DSI was less than 1 percent, but among individuals 80 years or older, fully 11.3 percent had DSI – dual hearing and vision loss.
A full report of the new study, Hearing Loss and Cognitive Decline in Older Adults, is found in the January 21, 2013 online edition of JAMA Internal Medicine, a journal of the American Medical Association.
A full report of the related research letter, The Prevalence of Concurrent Hearing and Vision Impairment in the United States, is also found in the January 21, 2013 online edition of JAMA Internal Medicine.
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