Occhealth Bulletin
02 November 2009
Sleep recovery after four successive night shifts
Category: Reviews
Over the last thirty years, research has been undertaken to determine the effects of night shift work on sleep, work performance and safety. Two schools of thought have emerged as a result: 1) shift work causes work performance to deteriorate over the course of successive nights and 2) performance and alertness improve over a period of successive night shifts. There has been little research carried out to determine the differences between individuals in their recovery after night shifts and the impact that recovery has on their normal work-life balance.
A research team in Japan has recently undertaken work to discover whether sleep recovery patterns were different between individuals and any factors that may have contributed to the patterns observed. Kubo and co-workers recruited ten male participants to the study all of whom had passed various criteria in order to take part. All were non-smokers and none had reported sleep disorders, undertaken shift work or traveled overseas in the three months prior to the study. One week before the study, the participants were banned from consuming beverages containing caffeine or alcohol, taking daytime naps, or depriving themselves of sleep. During the same week, the subjects were also required to keep a log of their sleeping and wakefulness patterns.
The participants stayed at a laboratory for the duration of the study and their sleep monitored using a wrist actigraph and sleep monitoring software. The first day involved adaptation to the environment followed by adaptation sleep (0:00-07:00). The second day involved baseline sleep (0:00-07:00) and day shift 1 (10:00-18:00). Beginning on the third day for four days were simulated night shifts (22:00-09:00) and day sleep periods (12:00-18:00). For the following three days (beginning on the eighth day) the participants had recovery sleep (0:00-07:00) with simulated day shifts on the ninth and tenth days (10:00-18:00). The shift periods involved undertaking tests (30 minutes) and tasks (computerized test battery; 20 minutes) followed by rest breaks for 10 minutes every hour. Free time allowed the participants to read books, listen to music, chat or watch television.
The researchers observed four patterns of sleep recovery after the simulated night shifts: rapid, slow, pseudo and incomplete. Those with rapid sleep recovery patterns almost had an immediate return to baseline sleep efficiency. Conversely, participants with ‘slow’ and ‘incomplete’ sleep recovery patterns showed slow recovery to baseline or no recovery on the third night after the night shift, respectively. Interestingly, participants exhibiting pseudo recovery patterns had poor sleep on the third recovery night despite transient recovery on the second night. The researchers reported that “the correlation analysis indicated that sleep habits (bed time and variation of wake time) prior to the experiment were significantly related to the recovery patterns, rather than performance and alertness during the night shifts”. The researchers concluded that although this study gave an insight into individual sleep recovery patterns, further research is needed on a larger number of participants and the factors (lifestyle, sex, physical or mental workload) that might influence those patterns.
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REFERENCE
Kubo, T., Takahashi, M., Tachi, N., Takeyama, H., Ebara, T., Inoue, T., Takanishi, T., Murasaki, G-i. and Itani, T. (2009) Characterizing recovery of sleep after four successive night shifts. Industrial Health. Volume: 47, pp 527-532.