Hearing loss increases dementia risk

Adults who experience hearing loss are at a higher risk of dementia andperhaps Alzheimer's disease than those who don't suffer hearing loss.

By the year 2050, an estimated 100million people or nearly one in 85 individuals worldwide will be affected bydementia. Unfortunately, there are no known current interventions that are effective.Studies have focused on the identification of putative risk factors that couldbe targeted for prevention based on the assumption that dementia is easier toprevent than to reverse. Candidate factors include low involvement in leisureactivities and social interactions, sedentary state, diabetes mellitus andhypertension.

To assess another potential risk factor,hearing loss, researchersstudied 639 American men and women aged between 35 and 90 years, none of whomhad dementia at the start of the study in 1990. Cognitive and hearing tests were conductedover a four-year period, followed by patient tracking through 2008 (for anaverage of about 12 years) to monitor for signs of dementia and/or Alzheimer's.

It was noted that 125 study participants had  "mild" hearing loss (25 to 40decibels),  53 had "moderate" loss (41 to70 decibels), while  six had "severe" loss (morethan 70 decibels). Ultimately, 58patients were diagnosed with dementia, of whom 37 had Alzheimer's disease.

By cross-referencing their data, it was found that mild hearing loss waslinked to a slight increase in dementia risk, but the risk increased noticeablyamong those with moderate and severe hearing loss. For participants aged 60years and older, more than 36 percent of dementia risk was linked to hearingloss, the study said. The worse the hearing loss, the worse the risk forAlzheimer's as well. For every additional loss of 10 decibels of hearingcapacity, Alzheimer's risk appeared to go up by 20 percent. There was noassociation between self-reported use of hearing aids and a reduction indementia or Alzheimer's disease risk.

The researchers postulate that anumber of mechanisms may be theoretically implicated. Dementia may beoverdiagnosed in individuals with hearing loss, or those with cognitiveimpairment may be overdiagnosed with hearing loss. The two conditions may sharean underlying neuropathologic process. Or, hearing loss may be causuallyrelated to dementia, possibly through exhaustion of cognitive reserve, socialisolation, or a combination of these pathways.

The findings suggest that there is astrong predictive association between hearing loss as an adult and thelikelihood of developing cognitive decline with ageing. With theincreasing number of people with hearing loss, research into the mechanismslinking hearing loss with dementia and the potential of rehabilitativestrategies to moderate this association are critically needed.