We comprehensively summarized the cohort evidence to date on adult-onset hearing loss as risk factor for incident cognitive impairment and dementia, and examined the evidence for dose-response, risk for various dementia subtypes, and other moderators. Previous meta-analyses were less comprehensive. We included cohort studies with participants without dementia and with hearing assessments at baseline, minimum 2 years follow-up and incident cognitive outcomes. We used random-effect models and subgroup and meta-regression on moderator analyses. We identified fifty studies (N=1,548,754). Hearing loss (yes/no) was associated with incident dementia risk (HR=1.35 [95% CI = 1.26 - 1.45), mild cognitive impairment (MCI HR=1.29 [95% CI = 1.11 - 1.50]), cognitive decline not specified as MCI or dementia (HR=1.29 [95% CI = 1.17 - 1.42]), and Alzheimer's disease dementia (ADD, HR=1.56 [95% CI = 1.30 - 1.87]), but not with vascular dementia (HR, 1.30 [95% CI = 0.83 - 2.05]). Each 10-decibel worsening of hearing was associated with a 16% increase in dementia risk (95% CI = 1.07 - 1.27). The effect of hearing loss did not vary across potential moderators. Cohort studies consistently support that adult-onset hearing loss increases the risk of incident cognitive decline, dementia, MCI, and ADD.

Background: Age-related hearing loss and mild cognitive impairment (MCI) independently increase dementia risk. The Ageing and Cognitive Health Evaluation in Elders randomised controlled trial (RCT) found hearing aids reduce cognitive decline in high-risk older adults with poor hearing. Methods: This pilot RCT in London memory clinics randomised people with MCI (aged ≥55, untreated hearing loss defined as Pure Tone Average 0.5–4 KHz between 25–70 dB) into two groups. The intervention group received 4 sessions of hearing aid fitting and support. The control group received healthy ageing education and a GP letter recommending audiological referral. Both were followed for 6 months. Primary outcomes were recruitment (feasibility target: 50%; 95% CI: 39%–61%) and retention (feasibility target: 80%; 95% CI: 71%–89%); intervention completion (≥2 visits) and hearing aid use (acceptability target: 80%; 95% CI: 71%–89%) for the intervention group and 50% difference between arms (95% CI: 31%–69%). Secondary outcomes included hearing aid fitting, cognition and other measures. Results: From October 2018 to March 2020, 58 participants were recruited (29 per group, 95% [86%–99%]). Twenty-four participants were fitted with hearing aids in the intervention arm, and 6 in the control arm (difference: 62% [42%–82%]). At 6 months, retention was 81% [69%–90%]. Hearing intervention completion (≥2 visits) was achieved by 24 (83%). Daily hearing aid use was reported by 18 (75%) intervention versus 5 (22%) control participants, a difference of 53% [29%–77%]. Conclusion: Randomisation of people with MCI to a personalised hearing intervention versus control is feasible. These findings support proceeding to a fully-powered multicentre RCT.