Hearing loss is a common part of aging, but for some people, it may be a sign of more serious problems in the brain.
Researchers in Italy examined two types of age-related hearing loss, peripheral and central. They concluded that people with central hearing loss had a higher risk of mild cognitive impairment (MCI) than those with no hearing loss or peripheral hearing loss.
Central hearing loss is caused by the brain’s impaired ability to process sound. Typically, people with this type of hearing loss can hear sounds, but can’t comprehend their meaning.
Study participants who had lower scores on a speech comprehension test also had lower scores on a test of thinking and memory skills.
Three-quarters of study participants with central hearing loss had MCI, compared to 60 percent of those with no hearing loss or peripheral hearing loss.
“These preliminary results suggest that central hearing loss may share the same progressive loss of functioning in brain cells that occurs in cognitive decline, rather than the sensory deprivation that happens with peripheral hearing loss,” said study lead author Rodolfo Sardone of the National Institute of Health and University of Bari.
This study was the first to separately examine the prevalence of MCI in central and peripheral hearing loss.
Researchers found a correlation between hearing loss and MCI, but no cause and effect.
“An important challenge for future studies is to elucidate whether there is a causal relationship between central hearing loss and cognitive function, or they might be simply complementary dependent measures of neurological degeneration with age,” Pinky Agarwal, a neurologist at the Booth Gardner Parkinson’s Care Center in Washington state, told Healthline.
What’s the connection?
Sardone said one possibility is that both issues are related to problems in the brain’s temporal cortex, specifically the superior temporal gyrus, “which is involved in executive function, working memory and language, and sound perception.”
Both hearing loss and MCI are known to involve neurodegeneration — the loss or death of neurons in the brain.
“The primary auditory cortex is the gateway to cortical processing of auditory input, since it receives information from the ascending auditory pathway,” explained Agarwal. “There are age-related changes in the primary auditory cortex. The memory areas are typically in the temporal cortex. Aging may involve both areas simultaneously.”
Tests of hearing perception should be given to people who are older than 65, as well as those with cognitive impairment, said Sardone.
“Hearing loss, both peripheral and central, is very associated with cognitive decline,” he told Healthline. “Preventing hearing impairment with hearing aids early could greatly reduce or delay the onset of cognitive neurodegeneration.”
“If hearing loss does contribute to cognitive decline, speech discrimination may be added as a screening for MCI,” said Agarwal.
MCI an early form of dementia?
MCI is characterized by difficulties with memory, language, thinking, and judgment that exceed those normally associated with aging.
Sardone described it as a “preclinical stage of dementia.”
“Hearing loss can lead to social isolation and depression that may exacerbate cognitive decline, and the constant perceptual effort resulting from reduced hearing acuity can be a source of stress and mental fatigue,” said Agarwal.
The study found that, overall, 33 percent of the 1,604 participants in the Great Age Study have MCI.
About 60 percent of individuals with no hearing loss or peripheral age-related hearing loss had MCI, and 75 percent of those with central hearing loss have the cognitive condition.
Among the study participants, who had an average age of 75, about 26 percent had peripheral age-related hearing loss — caused by problems in how the inner ear and hearing nerves function — and 12 percent had central hearing loss.
Hearing loss affects approximately 30 percent of the U.S. population aged 60 to 69 years. It increases to 63 percent among people aged 70 years and over.
Multiple past studies have also associated hearing loss with MCI and dementia.
The latest study will be presented in April at the American Academy of Neurology’s 70th annual meeting in Los Angeles.