Apolipoprotein E polymorphism ε4-stratified longitudinal association between daytime naps, sleep apnea and mild cognitive impairment: A prospective cohort study

Background and purpose: Sleep characteristics, including taking a nap and sleep apnea, have been proven to have effects on cognitive function, and apolipoprotein E polymorphism ε4 (APOEε4) has been confirmed to be a risk factor for mild cognitive impairment (MCI), but epidemiological studies linking sleep characteristics and APOEε4 are scarce. We aimed to explore the longitudinal association between sleep characteristics and MCI in an overall cohort, in APOEε4 carriers and in APOEε4 non-carriers.

Methods: We included 3053 older adults from the Tianjin Elderly Nutrition and Cognition Cohort (TENCC) study, recruited from March 2018 to June 2019, and followed up from March 2021 to June 2021. All participants underwent detailed neuropsychological evaluation that allowed psychometric MCI classification. Information on self-reported sleep characteristics was gathered via face-to-face interviews. Crude and multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazard regression models.

Results: In the multivariable-adjusted models, taking a nap at noon was associated with decreased risk of MCI in all participants (yes vs. no: HR 0.723, 95% CI 0.592, 0.883) and in APOEε4 non-carriers (yes vs. no: HR 0.719, 95% CI 0.576, 0.897). Sleep apnea was associated with increased risk of MCI in all participants (vs. good: HR 2.213, 95% CI 1.171, 4.180) and in APOEε4 non-carriers (vs. good: HR 2.217, 95% CI 1.085, 4.529).

Conclusions: This study suggests that taking a nap at noon might be a potential protective factor against development of MCI in APOEε4 non-carriers, and sleep apnea might be associated with increased incidence of MCI in APOEε4 non-carriers.