Both short and long sleep durations were associated with worse self-reported cognitive function and multiple lifestyle outcomes, suggesting a U-shaped association.
A recently conducted cross-sectional study demonstrated that short sleep duration was linearly associated with higher amyloid-beta (Aß) and worsened outcomes such as reduced cognition, greater depressive symptoms, and higher body mass index (MBI). Individuals who slept for at least 9 hours or "longer" sleep durations also demonstrated worsened outcomes except on Aß.
Lead author Joseph Winer, PhD, postdoctoral researcher, Stanford University School of Medicine, and colleagues sampled 4417 participants, aged 65 to 85 years, who underwent an Aß PET scan, had apolipoprotein E (APOE) genotype data, and were identified as clinically normal and cognitively unimpaired. Patients were grouped on self-reported nightly sleep duration (short sleep duration: ≤6 hours; normal sleep duration: 7-8 hours; long sleep duration: ≥9 hours).
Sleep duration was compared with demographic characteristics, Aß burden (as measured with a fluorine 18-labeled-florbetapir PET scan), objective and subjective cognitive function measures, and lifestyle variables. Via a lifestyle questionnaire, participants were asked to report their typical number of hours of sleep per night, minutes of daytime naps per day, and caffeinated and/or alcoholic drinks per day.
Investigators concluded that higher Aß burden was associated with fewer hours of nightly sleep (ß = –0.01 [standard error (SE), 0.00]; P = .005). When compared with normal sleep duration, associations remained only the short group (short vs normal sleep: ß = 0.01 [SE, 0.01]; P = .048; long vs normal sleep: ß = 0.00 [SE, 0.01]; P = .99). Winer et al wrote, that these associations "highlight the importance of maintaining adequate sleep in late life."
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Despite no significant linear associations observed between sleep duration and objective cognitive test performance, investigators noticed nonlinear associations on outcomes such as Mini-Mental State Exam (MMSE) and Logical Memory Delayed Recall (LMDR) test when categorized by short, normal, or long sleep duration. Significantly worse performances were observed for participants with short sleep duration on MMSE (ß = –0.08 [SE, 0.04]; P = .04) and LMDR (ß = –0.23 [SE, 0.11]; P = .03). Additionally, those participants were also less likely to obtain the maximum Free and Cued Selective Reminding Test (FCSRT) total recall score (ß = –0.18 [SE, 0.07]; P = .01).
Those in the shorter sleep duration group had linear associations with depressive symptoms, as measured on the Geriatric Depression Scale (GDS). When comparing all 3 groups, depressive symptoms were more prevalent in participants with shorter sleep (short vs normal sleep: ß = 0.31 [SE, 0.05]; P <.001) and longer sleep (long vs normal sleep: ß = 0.39 [SE, 0.09]; P <.001).
BMI was elevated in both short and long sleep duration groups, although no linear association was observed (short vs normal sleep: ß = 0.48 [SE, 0.17]; P = .01; long vs normal sleep: ß = 0.97 [SE, 0.31]; P = .002).
Investigators found no associations between sleep duration and caffeine consumption, whereas self-reported alcohol consumption had a linear association with nighttime sleep duration (ß = 0.07 [SE, 0.02]; P <.001). Consumption of alcoholic drinks was more frequent among those in the long sleep duration group compared to those in the normal (long vs normal sleep: ß = 0.38 [SE, 0.07]; P <.001) and short sleep duration groups (long vs short sleep: ß = 0.41 [SE, 0.08]; P <.001).
Those who spent more time daytime napping also were associated with less continuous nighttime sleep duration (ß = –0.86 [SE, 0.32]; P = .01) and were thus significantly elevated among both short and long sleep duration groups compared with normal (short vs normal: ß = 2.66 [(SE, 0.77); P = .001]; long vs normal: ß = –0.96 [(SE, 1.48); P = .52]). Notably, investigators found no significant interaction between nocturnal sleeping and daytime napping, except for FCSRT total recall performance (ß = –0.01 [SE, 0.01]; P = .03).