Background and Objectives Studies reporting an association between hearing loss and depression in older adults are conflicting and warrant a systematic review and meta-analysis of the evidence. Research Design and Methods A search of academic databases (e.g., MEDLINE) and gray literature (e.g., OpenGrey) identified relevant articles published up to July 17, 2018. Cross-sectional or cohort designs were included. Outcome effects were computed as odds ratios (ORs) and pooled using random-effects meta-analysis (PROSPERO: CRD42018084494). Results A total of 147,148 participants from 35 studies met inclusion criteria. Twenty-four studies were cross-sectional and 11 were cohort designs. Overall, hearing loss was associated with statistically significantly greater odds of depression in older adults (OR = 1.47, 95% confidence interval [CI] = 1.31−1.65). When studies were stratified by design, hearing loss was associated with greater odds of depression in cross-sectional studies (OR = 1.54, 95% CI = 1.31−1.80) and cohort studies (OR = 1.39, 95% CI = 1.16 − 1.67), and there was no difference between cross-sectional or cohort effect estimates (Q = 0.64, p = .42). There was no effect of moderator variables (i.e., hearing aid use) on the association between hearing loss and depression, but these findings must be interpreted with caution. There was no presence of publication bias but certainty in the estimation of the overall effect was classified as “low.” Discussion and Implications Older adults may experience increased odds of depression associated with hearing loss, and this association may not be influenced by study or participant characteristics.

Age-related hearing loss (ARHL), presbycusis, is a chronic health condition that affects approximately one-third of the world's population. The peripheral and central hearing alterations associated with age-related hearing loss have a profound impact on perception of verbal and non-verbal auditory stimuli. The high prevalence of hearing loss in the older adults corresponds to the increased frequency of dementia in this population. Therefore, researchers have focused their attention on age-related central effects that occur independent of the peripheral hearing loss as well as central effects of peripheral hearing loss and its association with cognitive decline and dementia. Here we review the current evidence for the age-related changes of the peripheral and central auditory system and the relationship between hearing loss and pathological cognitive decline and dementia. Furthermore, there is a paucity of evidence on the relationship between ARHL and established biomarkers of Alzheimer's disease, as the most common cause of dementia. Such studies are critical to be able to consider any causal relationship between dementia and ARHL. While this narrative review will examine the pathophysiological alterations in both the peripheral and central auditory system and its clinical implications, the question remains unanswered whether hearing loss causes cognitive impairment or vice versa.

Our results indicate that even in participants with a long duration, severe to profound hearing loss, cochlear implantation has some impact on improving a number of cognitive functions. This finding warrants future longitudinal investigations with a large sample size to examine if the observed cognitive enhancement benefits are sustainable.