In addition, some studies suggest that wearing hearing aids may help prevent dementia, though one study was recently voluntarily retracted due to methodological errors.
Given the overall evidence, how robust are these associations? And what guidance should clinicians provide to their patients?
Frank Lin, MD, PhD, a clinician and professor of otolaryngology and epidemiology at Johns Hopkins University School of Medicine, Baltimore, emphasized that the evidence from the past 10-15 years strongly links hearing loss to cognitive decline.
While quantifying the exact increase in risk is challenging, Dr. Lin said, “there’s no doubt about it; it’s not trivial.”
With respect to the potential link between hearing aids and dementia prevention, Dr. Lin is involved in the ongoing ACHIEVE randomized trial. Results presented at the 2023 Alzheimer’s Association International Conference and simultaneously published in The Lancet revealed participants who used hearing aids experienced a significant slowing of cognitive decline compared with those who received health education.
“It’s a no-risk intervention that can benefit social function, and for people at risk for cognitive decline, it can actually benefit cognitive health,” Dr. Lin said.
Potential Mechanisms
Dr. Lin pointed out that the Lancet Commission on Dementia identifies hearing impairment as one of the most significant risk factors for dementia. Overall, the consensus from most studies is that hearing loss definitely increases the risk for cognitive decline and dementia, he said.
Several hypotheses may explain this connection, and Dr. Lin believes that a combination of three key mechanisms is likely to be central to understanding this link.
The first theory focuses on cognitive load. As people experience age-related hearing changes, “the inner ear is no longer sending signals clearly to the brain,” Dr. Lin explained. This forces the brain to work harder, increasing its cognitive load as it reallocates resources to assist with hearing.
Dr. Lin emphasized that this is a hypothesis and does not prove hearing loss directly causes cognitive decline or dementia. Rather, it suggests that hearing loss accelerates the “unmasking” of cognitive issues. Brain resources that might otherwise buffer against dementia’s pathologic triggers are consumed earlier due to the demands of managing hearing loss.
The second potential mechanism suggests that hearing loss may have detrimental effects on brain structure and function over time — a theory supported by several recent studies.
These studies show that individuals with more severe hearing loss experience faster rates of brain atrophy. The reduced stimulation from poor auditory signals accelerates brain atrophy, Dr. Lin explained.
The third hypothesis focuses on social isolation. Individuals with hearing loss may engage less in social activities, reducing cognitive stimulation and overall social interaction. It’s well-known that social engagement and cognitive stimulation are crucial for maintaining cognitive health over time, Dr. Lin said.
Overall, Dr. Lin believes that the association between hearing loss and an increased risk for cognitive decline likely involves a combination of all three potential mechanisms. It’s not a matter of one theory being right and the others being wrong, he said.