In 2011 a groundbreaking study by Frank Lin, M.D., Ph.D., and colleagues at Johns Hopkins University showed that even a mild untreated hearing loss (not being able to hear a whisper) doubled the risk for dementia, with severe untreated hearing loss associated with a five-fold greater risk. Since then, there has been a growing body of evidence about the connection between hearing health and brain health. The Lancet followed up with not one but two reports (in 2017 and 2020) pointing to hearing loss as a modifiable risk factor to prevent cognitive decline and dementia.
Earlier this year, Samira Anderson, Au.D., Ph.D., a 2014 Emerging Research Grants scientist, showed that hearing aid use improved brain processing over time.
Now a December 2022 meta-analysis in JAMA Neurology shows that the use of hearing devices—hearing aids and cochlear implants—shows a quantifiable decrease in the risk of cognitive decline. (Emphasis added in all the excerpts.)
The report, by researchers in Singapore, says: “In this systematic review and multi-adjusted observational meta-analysis including 137,484 participants, the use of hearing restorative devices was associated with a 19 percent decrease in hazards of long-term cognitive decline such as incident dementia over a duration ranging from 2 to 25 years. Usage of these devices was also associated with a 3 percent improvement in cognitive test scores in the short term.”
The short term effects included research that showed improvements in memory after just 12 weeks of hearing aid use.
Why Are Hearing Loss and Cognitive Decline Linked?
In the discussion of the paper, the authors note that this association refutes the common cause hypothesis—that hearing loss and cognitive decline “occur independently as a result of a common mechanism such as age-related neurodegenerative processes involving vascular burden, oxidative stress, and genetics.”
They write, “Instead we have shown that there is a statistically significant benefit associated with hearing interventions, which could correct or prevent cognitive decline to a certain degree.”
The authors discuss the three leading theories for the connection between hearing loss and cognitive decline, and note the mechanism is likely to be multifactorial, a combination:
Cognitive load hypothesis: Individuals with hearing loss “may allocate high amounts of cognitive resources for auditory perceptual processing as they perform effortful listening…. Hence, fewer cognitive resources may be allocated for executive function and other cognitive tasks, including memory encoding. Thus, hearing restorative devices may reduce cognitive burden from listening, redirecting cognitive resources back to cognitive tasks.”
Sensory deficit hypothesis: The “lack of sensory input may lead to structural alterations, including atrophy. Imaging studies found that reduced volumes in the primary auditory cortex, whole brain, and especially the right temporal lobe were predicted by hearing impairment, and this atrophy affects cognitive ability that originates from similarly affected cortical areas.” (Dr. Lin published on the connection between hearing loss and brain atrophy, in 2014.)
Social isolation: “Hearing loss may be associated with social isolation, possibly due to difficulties in following conversation that result from hearing loss, causing individuals to withdraw from social activities. Multiple prospective studies have demonstrated strong relationships between social isolation and dementia.” The use of hearing devices can improve communication and social connectedness and reduce loneliness and isolation.
Encourage Hearing Assessment
While noting the study’s limitations (namely potential confounders such as education and wealth), an editorial in the same issue underscores one of the key takeaways—get hearing tested and, if needed, treat any hearing loss:
“…[W]e recommend physicians consider hearing evaluation as part of a standard dementia workup. Thanks to the recent creation of over-the-counter hearing aids, access to hearing loss treatment will increase. Clinicians have a unique opportunity to encourage hearing assessment and, if needed, use of hearing restorative devices such as hearing aids and cochlear implants. Not only can hearing loss contribute to symptoms of dementia, such as difficulty with communication, but hearing restoration remains an active area of investigation as a potential mitigator against the slow creep of cognitive decline. Simply put, assessment for hearing loss remains a crucial part of caring for patients with cognitive impairment.”
The bottom line? The use of hearing aids and cochlear implants is associated with a 19 percent decline in the risk for dementia. We should be shouting this from the rooftops. We know the risks to overall health from untreated hearing loss are myriad and wide-ranging. Hearing health is brain health.
Here is an overview of hearing tests, and here’s where to start if you are considering hearing aids. Let’s all take care of our hearing, for life. —Yishane Lee, HHF
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Our results suggest that mature cochlear supporting cells can be reprogrammed into sensory hair cells, providing a possible target for hair cell regeneration in mammals.