Why people lose hearing as they age
Researchers from Johns Hopkins and the National Institute on Aging have found that as the brain becomes smaller with age, the shrinkage seems to be fast-tracked in older adults with hearing loss.
The findings add to a growing list of health consequences associated with hearing loss, including increased risk of dementia, falls, hospitalizations, and diminished physical and mental health overall.
For the study, Frank Lin, M.D., Ph.D., and his colleagues used information from the ongoing Baltimore Longitudinal Study of Aging to compare brain changes over time between adults with normal hearing and adults with impaired hearing.
The Baltimore Longitudinal Study of Aging was started in 1958 by the National Institute on Aging to track various health factors in thousands of men and women.
Previous research from other studies had linked hearing loss with marked differences in brain structure compared to those with normal hearing, both in humans and animals.
In particular, structures that process information from sound tended to be smaller in size in people and animals with impaired hearing.
Lin, an assistant professor at the Johns Hopkins University schools of medicine and public health, says it was unknown, however, whether these brain structural differences occurred before or after hearing loss.
As part of the Baltimore Longitudinal Study of Aging, 126 participants underwent yearly magnetic resonance imaging (MRI) to track brain changes for up to 10 years. Each also had complete physicals at the time of the first MRI in 1994, including hearing tests. At the starting point, 75 had normal hearing, and 51 had impaired hearing, with at least a 25-decibel loss.
After analyzing their MRIs over the following years, Lin and his colleagues, reported that those participants whose hearing was already impaired at the start of the sub-study had accelerated rates of brain atrophy compared to those with normal hearing.
Overall, the scientists report, those with impaired hearing lost more than an additional cubic centimeter of brain tissue each year compared with those with normal hearing.
Those with impaired hearing also had significantly more shrinkage in particular regions, including the superior, middle and inferior temporal gyri, brain structures responsible for processing sound and speech.
"Our results suggest that hearing loss could be another 'hit' on the brain in many ways," Lin said.
The study is published in the journal Neuroimage.
(Posted on 24-01-2014)
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