Mid-life hearing loss
Hearing
Recognition of hearing loss as a risk factor for dementia
is relatively new and has not been included in previous
calculations of PAF, nor has it been a priority in the
management of those at risk of cognitive impairment.
Results of cohort studies65–67,81–88 that have investigated
hearing have usually shown that even mild levels of
hearing loss increase the long-term risk of cognitive
decline and dementia in individuals who are cognitively
intact but hearing impaired at baseline. However,
although there are 11 positive studies, two studies89,90
found no increased risk in adjusted analyses.
The risk of hearing loss for dementia in the metaanalysis
of three studies,65–67 which we did for this
Commission (pooled RR 1·94, 95% CI 1·38–2·73; figure 3),
is not only higher than the risk from other individual risk
factors, but it is also pertinent to many people because it is
highly prevalent, occurring in 32% of individuals aged
older than 55 years.91 Its high RR and prevalence explains
the high PAF. We have used the prevalence of hearing loss
in individuals older than 55 years to calculate PAF because
this age was the youngest mean age in which presence of
hearing loss was shown to increase dementia risk.67
Hearing loss is therefore grouped with the midlife risk
Late life
Hearing loss
Percentage reduction
if this risk is eliminated
Hypertension
Obesity
Early life
Midlife
ApoE ε4
Smoking
Depression
Physical inactivity
Social isolation
Diabetes
8%
9%
5%
5%
4%
3%
2%
1%
2%
1%
7%
Less education
Potentially
non-modifiable
65%
Potentially
modifiable
35%
Figure 4: Life-course model of contribution of modifiable risk factors to dementia
Numbers are rounded to nearest integer. Figure shows potentially modifiable or non-modifiable risk factors.
The Lancet Commissions
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factors, but evidence suggests that it continues to increase
dementia risk in later life.
The mechanism underlying cognitive decline associated
with peripheral hearing loss is not yet clear; nor is it
established whether correction, such as hearing aids,
can prevent or delay the onset of dementia. Older
age and microvascular pathology increase the risk of
both dementia and peripheral hearing loss, and might
therefore confound the association. Hearing loss might
either add to the cognitive load of a vulnerable brain
leading to changes in the brain,92 or lead to social
disengagement or depression93,94 and accelerated atrophy,95
all of which could contribute to accelerated cognitive
decline.96 Although impaired hearing might detrimentally
affect performance on formal cognitive assessments,
individuals with impaired baseline hearing had normal
baseline cognition so this cannot account for the findings.
Experimental evidence on whether hearing aid use
might alleviate some of these negative effects is not
available. Any intervention would require greater
complexity than merely suggesting to people that they use
a hearing aid because only a minority of people with
hearing loss are either diagnosed or treated,97 and when
hearing aids are prescribed many people do not use them.98
Central hearing loss is distinct from peripheral hearing
loss. It is a difficulty in understanding speech in noise
that is not explained by cochlear (peripheral) hearing
impairment and does not improve with peripheral
amplification (such as hearing aids).99 It is unlikely to be a
modifiable risk factor and could be a prodromal symptom
of Alzheimer’s disease causing impaired speech
perception, especially in the presence of competing
sounds.100 This theory is consistent with the fact that
central auditory areas are affected by Alzheimer’s disease
pathology.101 It is very unlikely that central hearing
impairment would account for the association between
peripheral hearing loss and dementia identified in
studies, because the central hearing loss that is followed
by Alzheimer’s disease is rare, at 2% of the older
population,100 while the prevalence of peripheral hearing
loss in the studies included in our meta-analysis in a
similar middle-aged and older population (mean ages in
the three included studies were 55 years, 64 years, and
75·5 years) is much larger (28%, 43%, and 58%,
depending on the specific study). Mild central hearing
loss might be more prevalent than the estimate of 2%, but
this has not been linked to increased risk of dementia.102
A small pilot intervention,103 Hearing Equality through
Accessible Research & Solutions (HEARS), used visual
materials and training for the participant and a family
member to increase usage of listening devices in
cognitively healthy adults with a mean age of 70 years.
The results of the pilot intervention showed that it might
be possible to increase their use.