Older adults with untreated hearing loss appear more likely to develop dementia, and their risk increases as hearing loss becomes more severe, according to a report in an issue of Archives of Neurology, one of the JAMA/Archivesjournals.
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 1 year could lead to a more than 10% decrease in the prevalence of dementia in 2050, the authors note. “Unfortunately, there are no known interventions that currently have such effectiveness,” they write.
Candidate risk factors for dementia include low involvement in leisure activities and social interactions, sedentary state, diabetes mellitus, and hypertension, and another potential risk factor is hearing loss.
To assess whether hearing loss is another potential risk factor, Frank R. Lin, MD, PhD, 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 (midpoint) 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 untreated 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 %) 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 %. 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.
The authors continue, “Finally, hearing loss may be causally related to dementia, possibly through exhaustion of cognitive reserve, social isolation, environmental deafferentation [elimination of sensory nerve fibers], or a combination of these pathways.”
If confirmed in other independent cohorts, the findings of the study could have substantial implications for individuals and public health.