Scientists see link between hearing loss and accelerated shrinkage of brain tissue

Frank Lin
Frank Lin

BALTIMORE, MD—Researchers from Johns Hopkins University and the National Institute on Aging have found a correlation between hearing loss in older adults and a faster rate of shrinkage of the brain than occurs among people of the same age with better hearing.

For their study, published in the journal NeuroImage, Frank Lin, MD, PhD, and his eight co-authors drew upon data from the National Institute on Aging’s Baltimore Longitudinal Study of Aging, which has been tracking various health factors in thousands of older men and women since 1958.

In 1994, the Baltimore study began conducting yearly magnetic resonance imaging (MRI) on 126 participants to track brain changes for up to 10 years. Hearing tests given to the subjects at the time of their first MRI showed that 51 of the subjects had a hearing loss of 25 dB or greater, and the other 75 had normal or closer to normal hearing.

After analyzing the MRI data over the years, Lin et al. determined that participants whose hearing was already impaired at the start of the study had accelerated rates of brain atrophy compared to those with more normal hearing. Specifically, they reported that those with hearing impairment lost more than one additional cubic centimeter of brain tissue each year than the other participants did. This group also had significantly greater shrinkage in particular regions, including the brain structures responsible for processing sound and speech: the superior, middle, and inferior temporal gyri.

In an interview with the Johns Hopkins Medicine media department, Lin said it was not surprising that the brain structures that process sound and speech were affected in those with hearing loss. He said that shrinkage in those areas might be a consequence of an “impoverished” auditory cortex, which could become atrophied from lack of stimulation.

However, he added that these structures have other functions that might be affected by shrinkage. For example, the middle and inferior temporal gyri play a role in memory and sensory integration and have been shown to be involved in the early stages of mild cognitive impairment and Alzheimer’s disease.

In the interview, Lin said, “Our results suggest that hearing loss could be another ‘hit’ on the brain in many ways.” Previous studies conducted by Lin and other scientists have found a number of health consequences associated with hearing loss, including increased risk of dementia, a higher incidence of falls, and diminished physical and mental health overall.

Lin, who is an assistant professor at the Johns Hopkins University Schools of Medicine and Public Health, said that this latest study offers another reason not to ignore hearing loss in its early stages. He said, “If you want to address hearing loss well, 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 colleagues plan to examine if treating hearing loss early can reduce the risk of associated health problems.