Ruminations: Linking Hearing Loss and Dementia

"It's really common, it's treatable, and there are interventions that come at no risk [that are underutilized]."
"[Preserving the ability to hear is foundational to public health] strategies that can best optimize the health of older adult populations, so older adults are living a long and full life 'till the very, very end."
"[Like daily step count, cholesterol level or weight], it's another metric that you would know about a dimension of your own health."
Dr. Frank Lin, director, Cochlear Center for Hearing and Public Health, Johns Hopkins Bloomberg School of Public Health

Global statistics tell us that worldwide, over 50,000 million people since 2019 are living with dementia. The forecast to the year 2050 is that the number will rise to over 130 million people in an aging population coping and living with dementia. Middle age hearing loss beginning at age 45 to 66 is considered by science to represent a significant risk factor for dementia. Hearing loss accounts for over eight percent of all dementia cases.

A Lancet report published in 2020 calculated that hearing loss generally doubles risk of dementia, similar to the increased risk caused by traumatic brain injury. Since hearing ability exists on a continuum, subclinical hearing loss can also contribute to a greater risk for dementia arising. According to Dr. Frank Lin, director of the Cochlear Center for Hearing and Public Health, remedially addressing hearing loss is a superior method of reducing the occurrence of dementia.

There is a hypothesis that suggests poor hearing increases the cognition load on the brain which in turn needs to work harder at the expense of other mental faculties in its attempt to decipher the garbled signals ears send to the brain when they're compromised. On the other hand, those with hearing loss and declining cognition struggle as well on tests not dependent on hearing, according to Dr. Tim Griffiths, professor of cognitive neurology, Newcastle University, Britain.

Animal model research and those with humans find that loss of hearing causes the brain to atrophy faster, particularly in the temporal lobe, possibly as a result of diminished use and lack of stimulation. Aberrant activity in the temporal lobe may also be caused by hearing loss, rendering it more susceptible to damage and pathologies associated with Alzheimer's disease, explains Dr. Griffiths.

Hearing loss -- the inability to connect with others -- can lead to social isolation, loneliness and depression, all factors known for the risk of dementia onset. The cochlea's sensory cells in the inner ear leads us to hear. Hair cells are sensory cells that translate the vibration of sound waves hitting eardrums into electrical signals sent to auditory regions of the brain to be decoded into sound.

Once hair cells become degraded or expire, the signals sent to the brain become garbled. Hair cells cannot be regenerated. Preliminary studies appear to affirm that the use of hearing aids tend to protect against dementia. Dr. Lin at the Johns Hopkins Bloomberg School of Public Health currently leads a large, randomized controlled trial with close to a thousand older adults in anticipation that the answer will more definitively emerge as to whether treating hearing loss with hearing aids reduces risk of cognitive decline.