Mechanisms linking hearing loss with risk for dementia depends on age.

Background: Age related hearing loss has been associated with increased prevalence and incidence of dementia. Underlying mechanisms that connect hearing loss with dementia remain largely unclear. Methods: We studied the association of hearing loss and other risk markers for dementia in two cohorts with normal cognition and different age: 65 participants from the EMIF‐AD 90+ study (mean age 92.7 years, 56.9% female) and 60 participants from the EMIF‐AD PreclinAD study (mean age 74.4, 43.3% female). Individuals were selected when they had hearing function ('digits‐in‐noise test') and neuropsychological testing available. Amyloid binding potential (BPND) was derived from dynamic PET scans. We used linear regression analysis and generalized estimating equations to test the association of hearing loss and BPND. We used linear mixed models to test the association of hearing function and cognition over time. In the oldest‐to‐old individuals, magnetic resonance imaging was available at the time of hearing function testing, and we performed mediation analyses to study whether cognitive decline is mediated through regional brain regions. All models included age, sex, and amyloid status as covariates, and longitudinal analyses were corrected for education years. Results: Oldest‐to‐old individuals showed worse hearing functioning than the younger cohort (p<.001). In oldest‐to‐old hearing loss was not associated with BPND (p =.70), whereas younger individuals showed an association of hearing loss with higher BPND (p =.003, figure 1). Oldest‐to‐old individuals showed associations of worse hearing with a steeper decline in memory (β ± SE = ‐0.018 ± 0.007), global cognition (β ± SE = ‐0.017 ± 0.007) and language (β ± SE = ‐0.014 ± 0.007), while in the younger cohort worse hearing was associated with steeper decline in language only (β ± SE = ‐0.086 ± 0.02, figure 2). Mediation analyses demonstrated that the hippocampus and nucleus accumbens fully mediate the effects of hearing loss on memory and global cognition in the older individuals (figure 3‐4). Conclusions: Hearing loss was associated with amyloid burden in younger individuals only, and with cognitive decline in both age groups. These results suggest that mechanisms linking hearing loss with risk for dementia depends on age. [ABSTRACT FROM AUTHOR]