Evaluating the link between hearing loss and Alzheimer's disease neuropathology: A systematic review and...

Hearing loss has been linked with cognitive decline and increased dementia risk. The neurobiological mechanisms underlying this relationship are not clear. In this systematic review and meta-analysis, we evaluated associations between hearing loss and Alzheimer's disease (AD) neuropathology, specifically β-amyloid (Aβ) and tau burden. Databases including PubMed, MEDLINE via Ovid, Web of Science, and EMBASE were searched to identify cohort and cross-sectional studies that examined the relationship between hearing loss and Aβ and/or tau neuropathology in humans. Meta-analyses were conducted using random-effects models and examined associations between hearing loss, either peripheral, central, or subjective, and in vivo AD neuropathology measured through PET or CSF. Estimates were converted to correlation coefficients prior to quantitative analysis. 6224 records were screened, of which 22 studies were included in the review. Significant associations between hearing loss and both Aβ (r, 0.09; 95 % CI, 0.02-0.16) and tau burden (r,0.16; 95 % CI, 0.08-0.23), were found across cross-sectional in vivo studies. However, in subgroup analyses, associations between Aβ burden and hearing loss were only significant for studies using central hearing measures or PET. Findings from studies in the systematic review, including post-mortem and longitudinal ones, were mixed. This study provides evidence for an association between hearing loss and AD neuropathology. The pattern of stronger meta-analytic findings localised to central hearing, PET, and tau studies suggests that higher levels of neuropathological burden may be linked to dysfunction in central auditory processing. The causality underpinning this relationship should be investigated in future studies.