New research has uncovered an increased risk of mild cognitive impairment (MCI) among individuals with a form of hearing impairment called central hearing loss. The findings suggest that this form of hearing loss may have a neurodegeneration-related mechanism at its root.

The National Institutes of Health (NIH) estimate that 15% of the adult population of the United States have a form of hearing loss.

Age is a significant risk factor for hearing loss. In fact, a quarter of US seniors aged between 65 and 74, as well as half of those aged over 75, have a disabling form of hearing loss.

Worldwide, a third of seniors have a disabling form of hearing loss.

A new study—led by Rodolfo Sardone, of the NIH and University of Bari in Italy—examines the link between a form of age-related hearing loss and the risk of developing MCI.

MCI is a type of cognitive decline that although noticeable is not significant enough to interfere with daily activities.

Research shows that between 15% and 20% of those aged 65 and above are likely to have MCI, which is also a risk factor for Alzheimer's disease.

The new study looked at both peripheral and central hearing loss. The former is due to problems in the inner ear and hearing nerves, while the latter affects the brain's sound processing abilities.

Sardone and his colleagues examined more than 1,600 people who participated in the Great Age Study, and the researchers' findings will be presented at the American Academy of Neurology's 70th annual meeting, due to be held in Los Angeles, CA, in April.

Hearing loss may double the risk of MCI

Sardone and colleagues had access to data on 1,604 participants in the Great Age Study, who were age 75 years, on average.

The participants were asked to undertake a series of hearing tests and have both their memory and reasoning tested.

Almost 26% of the study participants had peripheral hearing loss, and 12% had central hearing loss. Around 33% of the participants received a diagnosis of MCI, which was given using the well-established Petersen criteria.

Overall, people with central hearing loss were two times more likely to develop MCI compared with people whose hearing was intact.

More specifically, of the 192 people who had central hearing loss, 144 also had MCI. This amounts to 75%. By comparison, of the 609 people whose hearing was intact, 365 people had MCI, which amounts to 60%.

"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."

Rodolfo Sardone

"It's a problem with perception," he adds. As the study authors note in their paper, "No previous study has investigated speech discrimination and separate[d] the auditory perception from [the] auditory function."

"Tests of hearing perception," says Sardone, "should be given to people who are older than 65 and also to people with cognitive impairment."

But he also cautions that the study does not prove causality—that is, it does not demonstrate that hearing loss leads to memory loss. Rather, the research merely points to a link between the two.