Age-related reduction in daytime sleep propensity and nocturnal slow wave sleep

Abstract

Objective: To investigate whether age-related and experimental reductions in SWS and sleep continuity are associated with increased daytime sleep propensity.

Methods: Assessment of daytime sleep propensity under baseline conditions and following experimental disruption of SWS. Healthy young (20-30 y, n = 44), middle-aged (40-55 y, n = 35) and older (66-83 y, n = 31) men and women, completed a 2-way parallel group study. After an 8-h baseline sleep episode, subjects were randomized to 2 nights with selective SWS disruption by acoustic stimuli, or without disruption, followed by 1 recovery night. Objective and subjective sleep propensity were assessed using the Multiple Sleep Latency Test (MSLT) and the Karolinska Sleepiness Scale (KSS).

Findings: During baseline sleep, SWS decreased (P < 0.001) and the number of awakenings increased (P < 0.001) across the 3 age groups. During the baseline day, MSLT values increased across the three age groups (P < 0.0001) with mean values of 8.7 min (SD: 4.5), 11.7 (5.1) and 14.2 (4.1) in the young, middle-aged, and older adults, respectively. KSS values were 3.7 (1.0), 3.2 (0.9), and 3.4 (0.6) (age-group: P = 0.031). Two nights of SWS disruption led to a reduction in MSLT and increase in KSS in all 3 age groups (SWS disruption vs. control: P < 0.05 in all cases).

Conclusions: Healthy aging is associated with a reduction in daytime sleep propensity, sleep continuity, and SWS. In contrast, experimental disruption of SWS leads to an increase in daytime sleep propensity. The age-related decline in SWS and reduction in daytime sleep propensity may reflect a lessening in homeostatic sleep requirement. Healthy older adults without sleep disorders can expect to be less sleepy during the daytime than young adults.

Figure 1

MSLT (mean ± SE) at 9, 11, 13, 15, and 17 h, in young (•), middle-aged (○), and older subjects (▼). *P < 0.05; **P < 0.01; P < 0.001. Y vs. O = Young vs. Older; Y vs. M = Young vs. Middle-aged; M vs. O = Middle-aged vs. Older

Figure 2

MSLT (mean ± SE) in the Control (•) and SWS Disruption Group (○) on the Baseline (B) day, and the after one (D1) and two (D2) nights of SWS Disruption/Control and a Recovery (R) sleep episode. ***P < 0.001 Control vs. SWS Disruption.

Figure 3

Change from baseline for the MSLT (mean ± SE) at 5 time points during D1 and D2 in the Control (•) and SWS disruption (○) group. D1, D2 the days after one and two nights of SWS disruption/Control respectively *P < 0.05; **P < 0.01; *** P < 0.001 Control vs. SWS Disruption.

Figure 4

Change from Baseline for MSLT (Mean ± SE) at 5 time points during D2 in the Control (•) and SWS disruption (○) group in the young, middle-aged and older subjects. D2 is the days after two nights of SWS disruption/Control *P < 0.05; **P < 0.01; Control vs. SWS Disruption.