Obstructive sleep apnoea and risk of dementia: a Danish population-based cohort study.

Background: Obstructive sleep apnoea (OSA) is associated with adverse health outcomes. However, the association with dementia remains uncertain. Thus, we examined the association of OSA with all-cause dementia and Alzheimer's disease. Methods: We conducted a Danish nationwide population-based cohort study using health registries. Patients with OSA were identified from 1995 to 2017. Furthermore, a propensity score-matched comparison cohort was defined. Propensity scores were computed based on age, sex, comorbidities and education. With follow-up until 2018, we computed incidence rates (IRs) and HRs for all-cause dementia and Alzheimer's disease. Subgroup analyses were conducted by sex, age, overweight/obesity, hypertension and continuous positive airway pressure (CPAP) treatment. Results: We identified 62 928 patients with OSA and 62 928 in the propensity score-matched comparison cohort (76% male, median age 52 years). The IR for all-cause dementia was 1.27 (95% CI 1.17 to 1.37) per 1000 person-years in patients with OSA and 1.15 (95% CI 1.05 to 1.25) in the propensity score-matched comparison cohort, yielding an HR of 1.10 (95% CI 0.98 to 1.24). The HR for Alzheimer's disease was 1.16 (95% CI 0.94 to 1.43). Among individuals with overweight/obesity, the HR for all-cause dementia was 0.71 (95% CI 0.51 to 0.99), while it was 1.17 (95% CI 1.03 to 1.33) in those without. CPAP treatment attenuated associations. Conclusion: Our findings support a modest association between OSA and dementia, including Alzheimer's disease, motivating early clinical detection of OSA as a potentially modifiable risk factor for subsequent dementia. The finding that the dementia hazard was not increased in the setting of overweight or obesity requires further study and points to the need for research on mechanisms underlying the association between OSA and dementia.