Objectives: Hearing loss is a risk factor for dementia with estimated hazard ratios (HRs) of 1.28-2.39. However, whether intercontinental variability exists in this relationship remains unexplored.
Method: MEDLINE, PsychInfo, Academic Search Ultimate, Web of Science, and EMBASE were searched, from inception to 2024, for cohort studies of dementia-free individuals with baseline hearing assessments ≥2-year follow-up, and incident dementia outcomes. Random-effect and multilevel models with subgroup difference tests were conducted.
Results: Forty-nine studies analysed cohorts from North America (n = 20), Europe (n = 20), Asia (n = 7), and Oceania (n = 2). Binary hearing loss was associated with increased dementia risk (HR = 1.32 [95% CI: 1.23-1.41]) with HRs being largest for Oceania and smallest for Asia (p <0.001). In a sensitivity analysis excluding Oceania, HRs did not differ significantly by continent. Imprecise estimates create uncertainty around whether mild (HR = 1.35 [95% CI: 0.86-2.11]), moderate (HR = 1.39 [95% CI: 0.57-3.35]) or severe (HR = 1.66 [95% CI: 0.59-4.64]) hearing loss are associated with increased dementia risk, with little evidence that HRs by severity differ by continent (p = 0.059).
Conclusion: Findings indicate that the association between hearing loss and dementia is consistent globally, though HRs may vary slightly by continent.
Registration: This review was pre-registered on PROSPERO (CRD42024545209) and the OSF (https://osf.io/kew29/).
Keywords: Dementia; brain health; hearing loss; risk factors.