Even mild hearing loss predicted accelerated brain changes and increased dementia risk, with the strongest effects seen in genetically vulnerable adults.
Study: Hearing Loss, Brain Structure, Cognition, and Dementia Risk in the Framingham Heart Study. Image Credit: Alphavector / Shutterstock
In a recent study published in the journal JAMA Network Open, researchers investigated associations between hearing loss and cognitive function, brain structure changes, and dementia.
Age-related hearing loss has become increasingly prevalent as the population ages worldwide, and it may be a modifiable risk factor for dementia and cognitive decline.
The global prevalence of hearing loss ranges between 29 percent and 47 percent in people aged 65 years and older.
Several studies have found associations between hearing loss and poorer cognitive function, while others have linked it to smaller brain volumes or the risk of dementia.
Framingham Heart Study Used to Evaluate Brain and Cognitive Outcomes
In the present study, researchers investigated the associations of hearing loss with a wide range of brain-related outcomes and incident dementia.
The team used data from the Framingham Heart Study (FHS), a three-generational, prospective cohort study. The FHS offspring study cohort (second generation) enrolled 5,124 individuals in 1971 who were studied once every four years over 10 cycles.
Two partially overlapping samples were derived from participants who completed the sixth cycle (1995 to 1998) and a hearing assessment.
Sample 1 included participants who underwent cognitive assessment and brain magnetic resonance imaging (MRI) at the seventh and eighth examination cycles.
Sample 2 comprised people aged 60 years or older who were followed up for incident dementia analysis.
Detailed Hearing Assessments and Audiometry-Based Classifications
A questionnaire was administered to collect information on subjective hearing loss, head injury, otosclerosis, tinnitus, Ménière disease, dizzy spells, family history of hearing loss, use of ototoxic medications, noise exposure, and use of hearing aids. An audiologist performed pure tone threshold testing.
Hearing loss was separately analyzed for each ear using pure-tone averages (PTAs) at 0.5, 1, 2, and 4 kHz.
Neuropsychological Testing and MRI Measures of Brain Structure
Cognitive performance and decline were assessed using a battery of validated neuropsychological tests. T1-weighted brain MRI images were obtained, and the following measures were quantified: hippocampal volume (HPV), total cerebral brain volume (TCBV), and white matter hyperintensity volume (WMHV). Changes in these measures from the seventh to the eighth examination cycles were calculated.
Statistical Models Evaluating Dementia Risk and Brain Changes
Incidence of all-cause and Alzheimer's dementia was examined in sample 2. Multivariable linear regressions were performed to assess associations of PTA and hearing loss categories (no, slight, mild, or at least moderate hearing loss) with neuropsychological measures, TCBV, WMHV, and HPV, adjusting for age, sex, education, head size, and the time between hearing assessment and neuropsychological evaluation or baseline MRI.
The longitudinal associations of PTA and hearing loss categories with incident all-cause and Alzheimer's dementia were assessed using Cox proportional hazards regressions, adjusted for age, education, sex, and apolipoprotein E (APOE) ε4 carrier status.
Additional analyses adjusted for lifestyle and vascular covariates, including type 2 diabetes, systolic blood pressure, and smoking status.
The authors also examined whether adding hearing loss to a baseline dementia risk model modestly improved prediction accuracy.
Hearing Loss Associated With WMH Progression and Executive Decline
Sample 1 for MRI and cognitive analyses included 1,656 participants (mean age 58.1 years). Sample 2 comprised 935 individuals (mean age 67.6 years). Males had greater hearing loss than females, and the proportion with normal hearing decreased with age.
The team found a linear association between higher PTA thresholds and greater increases in WMHV, as well as greater declines in executive function. In contrast, memory and global cognition showed no significant associations with hearing loss.
WMHV increased more in people with at least slight hearing loss than in those with normal hearing. Individuals with at least mild hearing loss had a smaller TCBV at baseline and a greater decline in executive function. Adjustment for vascular and lifestyle factors did not alter these results.
Subjective hearing loss was also associated with poorer executive function and higher WMHV, even when audiometry did not indicate moderate or worse hearing loss, suggesting that self-report provides complementary information.
Dementia Risk Elevated in Individuals With Even Slight Hearing Loss
During 15 15-year follow-up, 12.7 percent of sample 2 developed dementia (77 percent Alzheimer's dementia). Individuals with at least slight hearing loss had a significantly higher risk of dementia than those with normal hearing (hazard ratio 1.71, CI 1.01–2.90).
The risk of dementia was significantly greater among APOE ε4 carriers with mild hearing loss than among those with normal hearing, suggesting a gene-environment interaction. Subjective hearing loss was also associated with higher dementia risk in ε4 carriers.
Participants with at least slight hearing loss who did not use hearing aids had a higher dementia risk, whereas hearing aid users showed a smaller and nonsignificant increase.
Exploratory sex analyses showed lower TCBV in men and faster WMHV progression in women. Adding hearing loss to dementia prediction models modestly improved risk discrimination metrics such as net reclassification index and integrated discrimination index.
Hearing Loss as a Potential Marker of Dementia Susceptibility
Taken together, objective hearing loss was associated with a significant increase in dementia risk, with categorical analyses showing a 71 percent higher risk for individuals with at least slight hearing loss.
Dementia risk was notably higher among APOE ε4 carriers with hearing loss than among those with normal hearing. Hearing loss was associated with accelerated executive decline, lower brain volume, and faster accumulation of white matter abnormalities, but not with memory or global cognition declines.
The findings suggest that hearing testing may help identify individuals at increased risk of dementia. However, the APOE ε4 interaction requires replication due to small subgroup sizes and modest estimate precision.
Overall, hearing loss should be viewed as a potential marker of increased dementia susceptibility, rather than evidence of causation, given the observational design, multiple comparisons, and imaging differences across study waves.
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