Does hearing loss lead to dementia? A review of the literature

• Published in: Hearing research Vol. 402; p. 108038
• Main Authors: Nadhimi, Yosra, Llano, Daniel A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-03-2021
• Subjects: Alzheimer; Alzheimer Disease - genetics; Animals; Cognition; Cognitive Dysfunction; Deafness; Dementia; Hearing Loss; Hippocampus; Noise-exposure; Presbycusis; Presbycusis - genetics; Tau; Tau; Noise-exposure; Alzheimer; Hippocampus; Presbycusis; Dementia; Hearing loss
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/j.heares.2020.108038

Recent studies have revealed a correlation between aging-related hearing loss and the likelihood of developing Alzheimer Disease. However, it is not yet known if the correlation simply reflects the fact that these two disorders share common risk factors or whether there is a causal link between them. The answer to this question carries therapeutic implications. Unfortunately, it is not possible to study the question of causality between aging-related hearing loss and dementia in human subjects. Here, we evaluate the research surrounding induced-hearing loss in animal models on non-auditory cognition to help infer if there is any causal evidence linking hearing loss and a more general dementia. We find ample evidence that induction of hearing loss in animals produces cognitive decline, particularly hippocampal dysfunction. The data suggest that noise-exposure produces a toxic milieu in the hippocampus consisting of a spike in glucocorticoid levels, elevations of mediators of oxidative stress and excitotoxicity, which as a consequence induce cessation of neurogenesis, synaptic loss and tau hyperphosphorylation. These data suggest that hearing loss can lead to pathological hallmarks similar to those seen in Alzheimer’s Disease and other dementias. However, the rodent data do not establish that hearing loss on its own can induce a progressive degenerative dementing illness. Therefore, we conclude that an additional “hit”, such as aging, APOE genotype, microvascular disease or others, may be necessary to trigger an ongoing degenerative process such as Alzheimer Disease.
•Aging-related hearing loss and Alzheimer Disease are epidemiologically linked.•We review the literature examining a potential causal association between the two.•There is ample evidence that noise and hearing loss lead to hippocampal dysfunction.•Noise-induced excitotoxic and oxidative stress cause hippocampal structural changes.•Future directions for research in this area are discussed.