A Global Burden Perspective on Obstructive Sleep Apnea, Hearing Loss, and Early-Onset Cognitive Decline

Background/Objectives: Cognitive decline and dementia represent a growing global crisis, affecting over 57 million individuals worldwide, projected to exceed 150 million by 2050. The 2024 Lancet Commission identified hearing loss as the single largest modifiable dementia risk factor (~7% population-attributable fraction). Obstructive sleep apnea (OSA), affecting ~936 million adults, is an increasingly recognized contributor yet remains underdiagnosed, especially in low- and middle-income countries (LMICs). This review synthesizes evidence on the global burden of cognitive decline associated with both conditions, evaluates causality debates, and identifies research gaps. Methods: Following SANRA guidelines, a search was conducted across PubMed, Scopus, Web of Science, and the Cochrane Library through February 2026. Original studies, systematic reviews, meta-analyses, and WHO/GBD reports were included; editorials and non-English publications were excluded. After deduplication, 3847 records were screened, and 96 studies met the inclusion criteria. Results: OSA has been linked to cognitive decline through several plausible mechanisms, including intermittent hypoxia, sleep fragmentation, impaired glymphatic clearance, and amyloid-beta accumulation, though the directionality of these associations requires confirmation from longitudinal studies. Hearing loss contributes to cognitive load, social isolation, and cortical reorganization. Both conditions disproportionately affect LMICs, where access to diagnosis and treatment remains limited. CPAP and hearing rehabilitation show cognitive benefits when initiated early, though evidence for reversing established impairment remains limited. A synergistic interaction between the two conditions is biologically plausible but empirically underexplored. Conclusions: OSA and hearing loss are highly prevalent conditions associated with increased dementia risk, though the certainty of causal relationships and the magnitude of intervention effects differ between the two conditions and across the available evidence. Integrated screening and early intervention could yield substantial neuroprotective benefits in high-risk populations and LMICs. Future longitudinal studies should examine combined cognitive trajectories and optimal intervention timing.