Elderly people with hearing loss have a greater chance of developing dementia, a risk that increases as their deafness worsens, according to a new report.
The research studied 639 individuals between the ages of 36 and 90 without dementia, who were given cognitive and hearing testing between 1990 and 1994.
The test subjects were followed for the development of dementia and Alzheimer's disease through May 2008, according to the study published in the February issue of the Archives of Neurology, a publication of the Journal of the American Medical Association (JAMA).
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 follow-up midway through the study, after about twelve years of research, 58 individuals were diagnosed with dementia, including 37 who had Alzheimer's disease.
The study found that the risk of dementia was higher 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.
Hearing loss may be causatively related to dementia, possibly through exhaustion of cognitive reserve, social isolation, environmental elimination of sensory nerve fibres or a combination of these pathways, reported the researchers, who are affiliated to the John Hopkins University in Baltimore, Maryland.
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, the report stated.
The researchers said that 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 per cent decrease in the prevalence of dementia in 2050, the authors wrote, but added that at present, unfortunately, there are no known interventions that currently have such effectiveness.