The loss of brain volume in humans seems to be fast-tracked in older adults with hearing loss, researchers have found.
The discovery adds to a growing list of health consequences associated with hearing problems, including increased risk of dementia, falls, hospitalizations, and diminished overall physical and mental health.
The new study by researchers from the Johns Hopkins University and the National Institute on Aging (NIA) also suggests it may be even more important than previously thought to treat hearing loss rather than ignore it.
“If you want to address hearing loss well,” lead investigator Frank Lin says, “you want to do it sooner rather than later. If hearing loss is potentially contributing to these differences we’re seeing on MRI, you want to treat it before these brain structural changes take place.”
Human brains do get smaller with age. Previous research, however, linked hearing loss to even more marked differences in brain structure than occurs in those with normal hearing.
In particular, structures that process sound tends to be smaller in people and animals with impaired hearing. It was not known, however, whether these brain structural differences arose before or after hearing loss, says Lin, assistant professor of medicine and public health.
Lin and his colleagues compared brain changes over time for adults with normal and impaired hearing. In NIA’s long-running Baltimore Longitudinal Study of Aging, 126 people underwent yearly magnetic resonance imaging 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 from the following years, Lin and his colleagues, writing for an upcoming issue of the journal Neuroimage, determined that those whose hearing was already impaired 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.
That structures responsible for sound and speech are affected in those with hearing loss wasn’t a surprise, says Lin; shrinkage in those areas might simply be a consequence of an “impoverished” auditory cortex, atrophied from lack of stimulation.
These structures don’t work in isolation, however, and their responsibilities don’t end at sorting out sounds and language, Lin says. The middle and inferior temporal gyri, for example, also play roles in memory and sensory integration and have been shown to be involved in the early stages of mild cognitive impairment and Alzheimer’s disease.
“Our results suggest that hearing loss could be another ‘hit’ on the brain in many ways,” Lin explains.
Lin and colleagues plan eventually to examine whether treating hearing loss early can reduce the risk of associated health problems.
The National Institute on Aging, the National Institute on Deafness and other Communication Disorders, a Triological Society/American College of Surgeons Clinical Scientist Development Award, and the Eleanor Schwartz Charitable Foundation supported the research.
Source: Johns Hopkins University