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. 2022 Mar 14;45(3):zsac006.
doi: 10.1093/sleep/zsac006.

Sleep deficiency in spaceflight is associated with degraded neurobehavioral functions and elevated stress in astronauts on six-month missions aboard the International Space Station

Christopher W Jones  1 , Mathias Basner  1 , Daniel J Mollicone  2 , Christopher M Mott  2 , David F Dinges  1
Affiliations

Sleep deficiency in spaceflight is associated with degraded neurobehavioral functions and elevated stress in astronauts on six-month missions aboard the International Space Station

Christopher W Jones et al. Sleep. .

Abstract

Astronauts are required to maintain optimal neurobehavioral functioning despite chronic exposure to the stressors and challenges of spaceflight. Sleep of adequate quality and duration is fundamental to neurobehavioral functioning, however astronauts commonly experience short sleep durations in spaceflight (<6 h). As humans embark on long-duration space exploration missions, there is an outstanding need to identify the consequences of sleep deficiency in spaceflight on neurobehavioral functions. Therefore, we conducted a longitudinal study that examined the sleep-wake behaviors, neurobehavioral functions, and ratings of stress and workload of N = 24 astronauts before, during, and after 6-month missions aboard the International Space Station (ISS). The computerized, Reaction SelfTest (RST), gathered astronaut report of sleep-wake behaviors, stress, workload, and somatic behavioral states; the RST also objectively assessed vigilant attention (i.e. Psychomotor Vigilance Test-Brief). Data collection began 180 days before launch, continued every 4 days in-flight aboard the ISS, and up to 90 days post-landing, which produced N = 2,856 RSTs. Consistent with previous ISS studies, astronauts reported sleeping ~6.5 h in-flight. The adverse consequences of short sleep were observed across neurobehavioral functions, where sleep durations <6 h were associated with significant reductions in psychomotor response speed, elevated stress, and higher workload. Sleep durations <5 h were associated with elevated negative somatic behavioral states. Furthermore, longer sleep durations had beneficial effects on astronaut neurobehavioral functions. Taken together, our findings highlight the importance of sleep for the maintenance of neurobehavioral functioning and as with humans on Earth, astronauts would likely benefit from interventions that promote sleep duration and quality.

Keywords: astronaut; sleep; sleep loss; spaceflight; stress; vigilant attention.

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Figures

Figure 1.
Figure 1.
The dynamics of sleep duration, PVT-B response speed, and astronaut stress ratings across mission phases. Means (± SEM) are presented for sleep duration (total sleep time [TST]; N = 1,418 TST measurements) in panels A–C, PVT-B response speed in panels D–F (N = 2,856 PVT-B measurements; a lower score on PVT response speed is slower), and ratings of stress in panels G–I (N = 2,541 stress measurements; VAS anchors: 100 = very stressed; 0 = not stressed). Given that ISS missions include both the pre-flight preparation and post-flight readjustment to Earth, as well as in-flight on the ISS, profiles of the three outcomes are first separated by mission phase (Panels A, D, G). In-flight profiles of TST, PVT-B response speed, and stress ratings are then presented across time-in-mission, by ISS mission quarter (Panels B, E, H). Data from these outcomes are also presented for in-flight weekdays and weekends, as well as sleep-shift vs. no sleep-shift (Panels C, F, I). Mixed-model analyses for statistical significance (p ≤ 0.05) for each data domain and mission time period are shown in the upper left-hand corner for mission phase and ISS mission quarter analyses (Panels A–B, D–E, G–H) and for Panels C, F, and I the left p-value refers to the weekday vs. weekend comparison and the right p-value refers to sleep shift vs. no sleep shift comparison (bolded p-values denote significance).
Figure 2.
Figure 2.
The impact of sleep duration on neurobehavioral functions during ISS missions. For all figure panels, sleep duration is binned into 1 h periods between ≤4 h and >9 h total sleep time (TST). In panel A, mean PVT-B response speed (N = 1,774 independent PVT-B assessments) is presented with 95% confidence intervals where larger numbers represent better performance. Sleep durations < 6 h were associated with slower PVT-B response speed; this is visualized using the gray diagonally lined bars (i.e. ≤4 h, 4 ≤ 5 h, and 5 ≤ 6 h TST), which represent significant pairwise differences from all dark gray bars (Supplementary Table S6). Conversely, longer sleep duration of TST > 9 h was associated with faster (i.e. higher) PVT-B response speeds relative to all groups with TST ≤ 7 h. Panels B–E present the least squares means ± SEM (adjusted for age, sex, and RST administration time of day) for astronaut ratings of somatic behavioral states, including physical exhaustion (B), mental fatigue (C), sleepiness (D), and tiredness (E) as a function of sleep duration (N = 1,703 independent ratings in each panel). For Panels B–E, the recommended sleep amount for healthy adults of 7–8 h (6) was used as the reference group (“REF”) and significantly higher astronaut ratings relative to the reference are colored red and significantly lower ratings are colored blue. Sleep durations < 5 h were associated with higher ratings of all somatic behavioral states, while longer sleep durations were associated with reductions in negative ratings of some somatic behavioral states (i.e. physical exhaustion [B], sleepiness [D], and tiredness [E]).
Figure 3.
Figure 3.
The impact of sleep duration on astronaut ratings of stress, workload, and sleep quality. Sleep duration is binned into 1 h periods between ≤4 h and >9 h total sleep time (TST). Least squares means ± SEM (adjusted for age, sex, and RST administration time of day) are presented for astronaut ratings of stress (A; N = 1,703 measurements), workload (B; N = 764 measurements), and sleep quality (C; N = 939 measurements) for each sleep duration grouping. The number of ratings within each sleep duration grouping is shown in white at the bottom of each bar; ratings of stress were collected in both morning and evening RST administrations, while workload (evening RST) and sleep quality (morning RST) were collected once on an RST testing day. The recommended sleep amount for healthy adults of 7–8 h (6) was used as the reference group (“REF”), and significantly higher astronaut ratings relative to the reference are colored red and significantly lower ratings are colored blue. Sleep durations < 6 h were associated with higher ratings of stress (A) while longer sleep durations were not associated with lower ratings of stress. Higher astronaut ratings of both workload (B) and worse sleep quality (C) were observed for sleep durations < 7 h, while longer sleep durations were associated with lower ratings of workload (B; > 8 h TST) and better sleep quality (C; > 9 h).
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