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LESSON 233

Hearing loss and dementia

Year 3
Fall semester
Geriatric Audiology
Aging and hearing
Duration: 11:50

Does hearing loss increase the risk of dementia, and do hearing aids reduce it? In this lesson we review hearing loss as a modifiable risk factor in the 2017, 2020 and 2024 Lancet Commission reports, the main and subgroup findings of the ACHIEVE trial (2023), the cognitive load and social isolation hypotheses, and how to explain this evidence accurately to patients.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will read through the evidence on the link between hearing loss and dementia together.
We will cover the Lancet Commission reports, the ACHIEVE trial, and how to explain these findings accurately in the clinic.
Dementia is a decline in cognitive functions such as memory, thinking and decision-making, severe enough to disrupt daily life.
Although it becomes more common with age, dementia is not an inevitable part of normal aging.
Its most common cause is Alzheimer's disease, thought to account for about 60 to 70 percent of cases.
Vascular dementia and other neurodegenerative diseases are also important causes.
According to World Health Organization data, about 57 million people worldwide were living with dementia in 2021.
Because there is no cure, factors that could reduce the risk are of great public health importance.
Mild cognitive impairment, a milder condition that can progress to dementia, does not always turn into dementia.
A modifiable risk factor is a risk factor that can be prevented or treated.
Hypertension, smoking, physical inactivity and hearing loss are examples of such factors.
Age and genetic predisposition, by contrast, are risk factors that cannot be changed.
A measure often used in the reports is the population attributable fraction.
It estimates how many dementia cases could in theory be prevented if a risk factor were removed from the population entirely.
But this calculation assumes the link between the factor and dementia is causal, and it does not mean individual risk.
The Lancet Commission used this measure to compare risk factors acting at different stages of life.
It was the dementia commission reports of The Lancet that moved hearing loss to the center of the dementia debate.
The 2017 report identified nine modifiable risk factors and suggested that about 35 percent of cases could in theory be prevented.
In this report, midlife hearing loss stood out as the single factor with the largest share, at about 9 percent.
The 2020 report raised the number of factors to twelve; the preventable share was about 40 percent, hearing loss about 8 percent.
The 2024 report added untreated vision loss and high LDL cholesterol, raising the number of factors to fourteen.
It gave a preventable share of about 45 percent; hearing loss and high LDL were the two largest factors, at about 7 percent each.
For this reason, the reports include wider access to hearing aids and protection from harmful noise among their recommendations.
The reports classify hearing loss as a midlife risk factor, so the window for prevention opens years earlier.
These reports rely largely on observational data from populations followed over long periods.
For example, a cohort study published in 2011 found that the risk of dementia rose as the degree of hearing loss increased.
The risk was about two times higher with mild loss and about five times higher with severe loss.
More recent studies reported that people with hearing loss who used hearing aids had a lower risk than those who did not.
But hearing aid users are generally healthier, more educated and have better access to health care.
So an observational association alone does not prove that hearing loss causes dementia, or that hearing aids prevent it.
A randomized controlled trial was needed to answer this question.
ACHIEVE, published in 2023, is the first large randomized controlled trial to test the effect of hearing intervention on cognitive decline.
The trial enrolled 977 people aged 70 to 84 in the United States.
Participants had previously untreated mild to moderate hearing loss and no significant cognitive impairment.
Participants were randomly assigned to two groups: a hearing intervention group and a health education group.
The hearing intervention included sessions with an audiologist, hearing aid fitting and counseling on communication strategies.
The primary outcome was the change in a global cognitive score over three years.
Some participants came from the long-running ARIC cardiovascular study, and others were new volunteers from the community.
Health education in the control group consisted of regular sessions on healthy aging topics.
When all participants were analyzed together, there was no significant difference in three-year cognitive decline between the groups.
So, on the primary outcome, the trial did not show that hearing intervention slowed cognitive decline in the general population.
Among about 740 healthy volunteers from the community, no difference between the groups was seen either.
The 238 people from the ARIC study, however, were older, had more risk factors and showed faster cognitive decline.
In this higher-risk subgroup, cognitive decline was about 48 percent slower in those who received the hearing intervention.
This finding comes from a prespecified sensitivity analysis; it is promising but does not count as conclusive proof on its own.
So it needs to be confirmed by new studies in populations with similar risk.
The primary outcome of ACHIEVE did not show that hearing intervention slows cognitive decline in everyone.
The subgroup finding suggests there may be a benefit for people at high risk of cognitive decline.
Because dementia develops over years, a three-year follow-up may have been too short to see an effect.
Long-term follow-up of the trial is ongoing, and future results may clarify the picture.
Remember that the benefits of hearing intervention for communication and daily life apply regardless of cognitive outcomes.
In short, treating hearing loss needs no dementia justification, but that justification should not be overstated beyond the evidence.
This picture also gives audiologists a responsibility: to follow the evidence and pass it on to patients as it is.
Several hypotheses have been proposed to explain the link; the first is the cognitive load hypothesis.
With hearing loss, the signal reaching the brain from the cochlea is weak and degraded.
The brain spends more effort decoding this degraded signal; this is called listening effort.
This effort may reduce the resources available for other functions such as memory and thinking.
Prolonged high listening effort may affect everyday cognitive performance.
Some imaging studies have reported faster volume loss in auditory regions in people with hearing loss; this is another possible pathway.
According to this hypothesis, a hearing aid could free cognitive resources for other functions by reducing listening effort.
According to the common cause hypothesis, aging and declining vascular health may affect the ear and the brain at the same time.
In that case hearing loss does not cause dementia; it is only an early marker of a shared process.
The cognitive load hypothesis, as we just saw, proposes that listening effort uses up cognitive resources.
According to the social isolation hypothesis, hearing loss makes communication harder and the person withdraws from social settings.
Reduced social contact and loneliness are also known risk factors for dementia.
The brain structure hypothesis argues that reduced auditory input may lead to structural changes in brain tissue.
These hypotheses are not mutually exclusive; more than one may play a role in the same person.
In the clinic, saying that hearing aids prevent dementia goes beyond the current evidence.
The accurate statement is: there is a strong link between hearing loss and dementia, and whether it is causal is being studied.
A fear-based message may seem persuasive in the short term, but it can damage trust.
The proven main benefit of hearing aid use is better communication and greater participation in social life.
This benefit improves quality of life by strengthening the person's ties with family and friends.
If there is a clear complaint about memory or thinking, the person should be referred to a physician for assessment.
Including the family in the session makes it easier to apply communication strategies at home.
A tip from the field: most cognitive screening tests rely on verbal instructions and word repetition.
A person with hearing loss may answer wrongly because they did not hear the question, and score lower than they really are.
So it is important to assess, or at least ask about, hearing before cognitive screening.
Using a personal amplifier, choosing a quiet room and also showing the instructions in writing reduce this error.
Versions of cognitive screening tests adapted for hearing loss have also been developed for this purpose.
In this lesson we saw that the Lancet Commission ranks hearing loss among the largest modifiable risk factors.
Observational studies show a strong link, but this link alone is not evidence of cause and effect.
ACHIEVE showed no effect in the general population, but cognitive decline slowed in a higher-risk subgroup.
In the clinic, this evidence should be explained without overstatement, stressing that the main benefit is communication.
Test yourself: in the ACHIEVE trial, what was the primary outcome across all participants?
The correct answer is B: there was no significant difference between the two groups.
The slowing of about 48 percent was seen only in the higher-risk ARIC subgroup.
In the next lesson we will cover hearing aid fitting for older adults, with cognitive screening, dexterity and caregiver involvement.
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Prerequisites

LESSON 232 The Aging Auditory System: Peripheral and Central Coming soon

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