January 22, 2013
Hearing Loss Linked To Cognitive Decline In The Elderly
April Flowers for redOrbit.com - Your Universe Online
This study is significant as the prevalence of dementia is projected to double every 20 years because of the world's aging population so identifying the factors and understanding the pathways that lead to cognitive decline and dementia in older adults is a public health priority.
Study participants with hearing loss underwent repeated cognitive testing over six years and showed cognitive abilities that declined 30 to 40 percent faster than those whose hearing was in the normal range. The research team finds a direct correlation between the amount of hearing loss and levels of brain function decline. Older adults with hearing loss, on average, developed a significant impairment in their cognitive abilities 3.2 years sooner than those with normal hearing.
Reported online in the JAMA journal Internal Medicine, these findings are among the first to emerge from a larger study — known as the Health, Aging and Body Composition, or Health ABC study - monitoring the health of older black and white individuals in Memphis, Tennessee and Pittsburgh, Pennsylvania. Believed to be the first study to investigate the impact of hearing loss on brain function over the long-term, these findings concern a subset of 1,984 men and women between the ages of 75 and 84. According to Frank Lin, M.D., Ph.D., Johns Hopkins otologist and epidemiologist, all participants had normal brain function when the study began in 2001, and were initially tested for hearing loss, defined as recognizing only those sounds louder than 25 decibels.
"Our results show that hearing loss should not be considered an inconsequential part of aging, because it may come with some serious long-term consequences to healthy brain functioning," says Lin, an assistant professor at the Johns Hopkins University School of Medicine and the university's Bloomberg School of Public Health.
"Our findings emphasize just how important it is for physicians to discuss hearing with their patients and to be proactive in addressing any hearing declines over time," says Lin. As many as 27 million Americans over age 50, including two-thirds of men and women aged 70 years and older, Lin estimates, suffer some form of hearing loss, with only 15 percent of those needing a hearing aid actually receiving one.
Lin asserts that possible explanations for the cognitive slide include the ties between hearing loss and social isolation, with loneliness being well established in previous research as a risk factor for cognitive decline. Too much energy might be diverted by the brain to dealing with processing sound at the expense of memory and thinking because of degraded hearing. There might also be other underlying damage or health issues that have led to this loss of hearing and cognitive function.
All participants were in good health at the study's onset in 1997. In 2001, volunteers were given hearing tests, during which they individually listened to a range of soft and loud sounds, from 0 decibels to 100 decibels, in a soundproof room.
Again in 2001, brain function was also assessed using two well-recognized tests of memory and thinking ability; the Modified Mini-Mental State (3MS) and Digit Symbol Substitution (DSS), respectively. Participants were asked to memorize words, given commands or instructional tasks to follow, and asked basic questions as to the correct year, date and time in the 3MS study. In contrast, in the DSS test, participants were asked to match specific numbers to symbols and timed on how long it took them to complete the task. Both tests were repeated for each subject three more times until the study ended in 2007. The analysis accounted for factors already know to contribute to loss of brain function including age, high blood pressure, diabetes and stroke.
"Our results demonstrate that hearing loss is independently associated with accelerated cognitive decline and incident cognitive impairment in community-dwelling older adults," the authors comment. "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."
"In conclusion, our results suggest that hearing loss is associated with accelerated cognitive decline and incident cognitive impairment in older adults. 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 study concludes.
Lin and his colleagues are planning to launch a much larger study designed to test whether hearing aids or other devices might slow or forestall the loss of cognitive decline.