Objectives This study investigated whether an intervention designed to reduce homeostatic sleep pressure would improve night shift performance and alertness in older adults.
Methods Non-shift workers aged 57.9±4.6 (mean±SD) worked four day (07:00–15:00) and four night shifts (23:00–07:00). Two intervention groups were instructed to remain awake until ~13:00 after each night shift: the sleep timing group (ST; n=9) was instructed to spend 8 hours in bed attempting sleep, and the sleep ad-lib group (n=9) was given no further sleep instructions. A control group (n=9) from our previous study was not given any sleep instructions. Hourly Karolinska Sleepiness Scales and Psychomotor Vigilance Tasks assessed subjective sleepiness and performance.
Results The ST group maintained their day shift sleep durations on night shifts, whereas the control group slept less. The ST group were able to maintain stable performance and alertness across the initial part of the night shift, while the control group’s alertness and performance declined across the entire night. Wake duration before a night shift negatively impacted sustained attention and self-reported sleepiness but not reaction time, whereas sleep duration before a night shift affected reaction time and ability to sustain attention but not self-reported sleepiness.
Conclusions A behavioural change under the control of the individual worker, spending 8 hours in bed and waking close to the start of the night shift, allowed participants to acquire more sleep and improved performance on the night shift in older adults. Both sleep duration and timing are important factors for night shift performance and self-reported sleepiness.
- shift work
- circadian rhythms
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Contributors JFD designed the research. CMI, EDC, JHK and ASM collected and processed the data. CMI, WW and JFD analysed the data. CMI and JFD wrote the paper. All authors reviewed and approved the paper.
Funding The studies were supported by National Institutes of Health (NIH) grant R01 AG044416 and were performed in the Brigham and Women’s Hospital Center for Clinical Investigation, part of Harvard Catalyst (Harvard Clinical and Translational Science Center) and supported by NIH Award UL1 TR001102 and financial contributions from Brigham and Women’s Hospital and from Harvard University and its affiliated academic healthcare centers. EDC was supported by NIH fellowship T32 HL007901. JHK was supported by a grant from Dankook University. CMI and JFD were supported in part by NIH grant P01 AG09975 during the analysis.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval. The protocol was reviewed and approved by the Partners Health Care Human Research Committee [Protocol 2012-P-002485]. Signed informed consent was obtained from each participant prior to their enrollment.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement De-identified actigraphy, PVT, and KSS data are available from the corresponding author upon request. A Data Sharing Agreement that specifies the specific data requested and the plans for use, along with the requestor's IRB approval for the data use, and signed by the requestor and corresponding author, must be executed prior to sharing data.