Age-related hearing loss and cognitive decline — The potential mechanisms linking the two

The amount of attention to age-related hearing loss (ARHL) has been growing, not only from the perspective of being one of the most common health conditions affecting older adults, but also from the perspective of its relation to cognition. Results from a number of epidemiological and laboratory studies have demonstrated a significant link between ARHL and cognitive decline. The Lancet International Commission on Dementia, Prevention, Intervention, and Care has estimated that mid-life hearing loss, if eliminated, might decrease the risk of dementia by nine percent, since hearing loss is a modifiable age-associated condition linked to dementia. Despite numerous research efforts, elucidation of the underlying causal relationships between auditory and cognitive decline has not yet reached a consensus. In this review article, we focused on the hypotheses of etiological mechanisms between ARHL and cognitive decline: (1) cognitive load hypothesis; (2) common cause hypothesis; (3) cascade hypothesis; and (4) overdiagnosis or harbinger hypothesis. Factual evidence obtained in previous studies was assessed to understand the link between ARHL and cognitive decline or dementia. Additionally, an overview of the conceivable effects of hearing intervention, e.g., hearing aids and cochlear implants, on cognition were presented, and the role of hearing aid use was considered for the relevant hypotheses. We should continue to strive for social enlightenment towards the importance of ‘hearing well’, and cultivate a necessity for hearing screening among patients at risk of cognitive decline.