Interrelationship of Sleep Disturbances and Cognitive Status on Mortality

Abstract

Sleep disturbances may promote the development and advancement of Alzheimer's disease. Our purpose was to determine if sleep disturbances were associated with earlier mortality while accounting for cognition. The National Alzheimer's Coordinating Center database was used to evaluate mortality risk conferred by sleep, and the Montreal Cognitive Assessment score determined cognitive status. Demographics, sleep disturbances, cognitive status, and comorbid/other neuropsychiatric conditions were examined as predictors of survival time via Cox regression. The sample (N = 31,110) had a median age [interquartile range] of 72 [66, 79] years, MoCA score of 23 [16, 26], and survival time of 106.0 months [104.0,108.0]; 10,278 (33%) died during follow-up; 21% (n = 6461) experienced sleep disturbances. Sleep disturbances impacted survival time depending on cognition, with the greatest effect in transition from normal to cognitive impairment (P < .001). Findings support that sleep disturbances negatively impact survival time, and the impact of sleep disturbances on survival time is interrelated with cognition.

Keywords: Alzheimer’s disease; cognitive dysfunction; mortality; sleep; sleep disorders; sleep-wake disorders.

Figure 1.

Kaplan-Meier curves for the predictors of survival time. Black lines indicate the reference stratification category.

Figure 2.

Sleep disturbances impact on the instantaneous death rate function of MoCA visit #1 score, when quantified by the Cox piecewise multiple regression model predicted adjusted hazard ratio (AHR) in MoCA score cognitive category intervals: normal cognition: [26, 30], mild impaired cognition (MCI): [20, 25], and dementia: [0, 19]. Solid back circles identify the AHR, and solid vertical lines identify the AHR 95% confidence interval, and the red horizonal solid line identifies the point on the y-axis where the AHR is equal to 1. Note that each null hypothesis assumes an underlying AHR equal to 1, and therefore if the AHR lower 95% confidence limit is located below or on the red solid line, the null hypothesis fails be rejected at the α = .05 significance level.