Loneliness as a pathway linking hearing decline to cognitive aging: Longitudinal and genetic evidence

Hearing loss and loneliness are potentially modifiable risk factors for cognitive decline and dementia, but it remains unclear whether loneliness represents a causal pathway linking hearing loss to cognitive aging or whether these associations reflect shared vulnerability.

We combined up to 18 years of data from the Survey of Health, Ageing and Retirement in Europe (SHARE; N = 10,375) with summary statistics from eight primary genome-wide association study sources and an independent neuroticism dataset used in sensitivity analyses. Parallel-process latent growth curve models examined level and change associations; additional analyses evaluated hearing-aid moderation, Mendelian randomization, multivariable Mendelian randomization, and colocalization.

At Wave 7, poorer hearing, greater loneliness, and poorer word-recall performance were associated, with a significant indirect association through loneliness. Evidence for coordinated longitudinal mediation was limited, and the primary change-to-change indirect effect was not significant. Current, but not cumulative, hearing-aid use was associated with a weaker concurrent hearing-loneliness association. Genetic analyses provided little evidence for direct or loneliness-mediated causal effects of hearing phenotypes on Alzheimer's disease or all-cause dementia. Results were more consistent with shared liability, including overlap with neuroticism.

The findings support late-life associations among hearing difficulty, loneliness, and cognitive performance but provide limited evidence that loneliness is a primary causal pathway linking hearing loss to cognitive aging. Integrating longitudinal and genetic evidence suggests a more complex etiology involving shared liability and supports direct evaluation of hearing care and social connection in intervention studies.