Cognitive dysfunction
Association in Longitudinal Cohorts
Age-related hearing loss is repeatedly associated with accelerated cognitive decline and higher incidence of dementia in large observational studies, called longitudinal cohorts, a group of people assessed and followed repeatedly over time to observe how earlier exposures, like hearing loss, relate to later outcomes, like dementia.
Population-Attributable Fraction (PAF) and Causality
Observational studies make population-attributable fraction estimates, or PAF, which are estimates of the proportion of cases in a population that could be avoided if a risk factor were eliminated, assuming causality. Causality is the relationship between one thing and another, in this case, hearing loss and dementia.
How to Read Public Health Signals
As we have said before, public health data are imprecise but directionally accurate, meaning that if you are a public health researcher you can rely on the data to point you in the right direction. So what does the data tell us?
Lancet Commission Findings and the Size of the Risk
Lancet Commission on Dementia reports (2020, 2024) list hearing impairment among the leading potentially modifiable dementia risk factors. The reports provide PAF estimates showing hearing loss contributes meaningfully to dementia burden at the population level. PAF estimates range from 9% to 32%, but even conservative estimates signal considerable public health impact.
Causality is the caveat that drives the estimated range. Cohort studies enable researchers to interrogate causal relationships between hearing loss and dementia, but the precise relationship between these two conditions is still being clarified. The important point is that public health data raise awareness and shape research funding, which ultimately leads to interventions.
Pathway 1: Cognitive Load (Listening Effort)
Researchers often describe a cascade of three biological and behavioural pathways linking hearing loss to cognitive dysfunction. Cognitive load, processing bottlenecks in the brain, is an upstream triggering condition. Hearing loss degrades auditory input, forcing the brain to exert increased effort to listen and understand, diverting cognitive resources away from other tasks. (PubMed Central, Frontiers in Dementia)
Pathways 2 & 3: Sensory Deafferentation and Brain Change
Sensory deafferentation and brain change are downstream effects. Over the long term, reduced auditory input from the inner ear is associated with structural brain changes. Atrophy begins in regions responsible for auditory and temporal signal processing.
The brain’s temporal lobe, just above your ears, decodes timing and patterns of sounds and speech, telling the brain when sounds happen so you can understand words and speech clarity. Think of temporal processing as the brain’s clock, keeping time on the order of sound in words and the rhythm of speech. Synaptopathy significantly degrades temporal processing. Read more about synaptopathy on our tinnitus & hyperacusis page.