Elderly people with severe hearing
loss more likely to develop dementia than those with less impairment
Older adults with hearing loss appear more likely to
develop dementia, and their risk increases as hearing loss becomes more severe,
according to a report in the February issue of Archives of Neurology, one of the
JAMA/Archives journals.
By the year 2050, an estimated 100 million people or nearly one in 85 individuals
worldwide will be affected by dementia, according to background information in
the article. Interventions that could delay the onset of dementia by even one
year could lead to a more than 10 percent decrease in the prevalence of dementia
in 2050, the authors note. "Unfortunately, there are no known interventions
that currently have such effectiveness," they write. "Epidemiologic
approaches have focused on the identification of putative risk factors that could
be targeted for prevention based on the assumption that dementia is easier to
prevent than to reverse. Candidate factors include low involvement in leisure
activities and social interactions, sedentary state, diabetes mellitus and hypertension."
To assess another potential risk factor, hearing loss, Frank R. Lin, M.D.,
Ph.D., of Johns Hopkins Medical Institutions, Baltimore, and colleagues studied
639 individuals age 36 to 90 without dementia. Participants initially underwent
cognitive and hearing testing between 1990 and 1994 and were followed for the
development of dementia and Alzheimer's disease through May 31, 2008.
Of the participants, 125 had mild hearing loss (25 to 40 decibels), 53 had
moderate hearing loss (41 to 70 decibels) and six had severe hearing loss (more
than 70 decibels). During a median follow-up of 11.9 years, 58 individuals were
diagnosed with dementia, including 37 who had Alzheimer's disease.
The risk of dementia was increased among those with hearing loss of greater
than 25 decibels, with further increases in risk observed among those with moderate
or severe hearing loss as compared with mild hearing loss. For participants age
60 and older, more than one-third (36.4 percent) of the risk of dementia was associated
with hearing loss.
The risk of developing Alzheimer's disease specifically also increased with
hearing loss, such that for every 10 decibels of hearing loss, the extra risk
increased by 20 percent. There was no association between self-reported use of
hearing aids and a reduction in dementia or Alzheimer's disease risk.
"A number of mechanisms may be theoretically implicated in the observed
association between hearing loss and incident dementia," the authors write.
Dementia may be overdiagnosed in individuals with hearing loss, or those with
cognitive impairment may be overdiagnosed with hearing loss. The two conditions
may share an underlying neuropathologic process. "Finally, hearing loss may
be causally related to dementia, possibly through exhaustion of cognitive reserve,
social isolation, environmental deafferentation or a combination of these pathways."
"If confirmed in other independent cohorts, the findings of our study
could have substantial implications for individuals and public health. Hearing
loss in older adults may be preventable and can be practically addressed with
current technology (e.g., digital hearing aids and cochlear implants) and with
other rehabilitative interventions focusing on optimizing social and environmental
conditions for hearing. With the increasing number of people with hearing loss,
research into the mechanistic pathways linking hearing loss with dementia and
the potential of rehabilitative strategies to moderate this association are critically
needed."
This work was supported by the Intramural Research Program of the National
Institute on Aging and a grant from the National Institute on Deafness and Other
Communication Disorders.
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