In general, the brain becomes smaller with age. But the shrinkage seems to be fast-tracked in older adults with untreated hearing loss, according to the results of a study by researchers from Johns Hopkins and the National Institute on Aging.
For the study, researcher Frank Lin, M.D., Ph.D. and his colleagues at Johns Hopkins Medicine in the US used information from the Baltimore Longitudinal Study of Aging to compare brain changes over time between adults with normal hearing and adults with hearing loss.
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 while 51 had impaired hearing, with at least a 25dB loss.
Lost more brain tissue
After analyzing their MRIs over the following years, Lin and his colleagues found 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, those with impaired hearing lost more than an additional cubic centimetre of brain tissue each year compared with those with normal hearing. Those with impaired hearing also had significantly more shrinkage in particular regions, including brain structures responsible for processing sound and speech.
That structures responsible for sound and speech are affected in those with hearing loss was not a surprise to the researchers. Shrinkage in those areas might simply be a consequence of an "impoverished" auditory cortex, which could become atrophied from lack of stimulation. However, these structures do not work in isolation and their responsibilities do not end at sorting out sounds and language.
Treat the hearing loss
"The study gives some urgency to treating hearing loss rather than ignoring it. If you want to address hearing loss well," 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."
Lin and his colleagues plan to examine whether treating hearing loss early can reduce the risk of associated health problems.
The findings add to a growing list of health consequences associated with hearing loss, including increased risk of dementia, falls, hospitalisations and diminished physical and mental health overall.