A recent study found that people with intermediate and late chronotypes had more rapid eye movement sleep when they delayed their sleep before their first night shift.
Individuals who have an intermediate or late sleep chronotype, a difference that reflects circadian phase, benefitted from delaying their main sleep before a night shift via an increase in rapid eye movement (REM) sleep and from being generally more awake, according to a new study published in Journal of Sleep Research.
In the first night shift in a sequence of them, alertness, vigilance, and attention are often at their worst, according to previous studies on the subject. Circadian misalignment is thought to be exacerbated before night shifts, which leads to sleep deprivation in many workers.
A simulated shift work study was conducted at the Appleton Institute in Adelaide, South Australia. There were 71 adults with a mean (SD) age of 23.1 (3.6) years included in this study. Participants needed to be aged 18 to 30 years and have good physical, mental, and sleep health to be included in the study.
All data were collected in the first 2 days of the simulated work shift study. Participants slept at 2 opportunities: normally timed sleep (night 1, 23:00-08:00) and delayed sleep (night 2, 03:00-12:00). Napping was not permitted. Participants were asked to maintain their regular sleep schedules in the week prior to the study. Exclusion criteria included if they smoked, used medication other than oral contraceptives, used recreational drugs, had excessive alcohol or caffein consumption, excessively exercised, and had shift work or transmeridian travel in the prior month.
A tertile split was used to determine early, intermediate, and late chronotypes. The researchers found a difference in sleep onset between early and late chronotypes and a difference in sleep offset between early and intermediate and early and late chronotypes. Phase angles were also different between early and late chronotypes and intermediate and late chronotypes.
Chronotype and sleep timing had interactions with total sleep time, sleep efficiency, and REM. Participants with early chronotypes had less total sleep time and sleep efficiency with delayed sleep compared with normally timed sleep whereas intermediate and late chronotypes had similar totals for sleep time and efficiency in both sleep opportunities.
REM was similar in both sleep opportunities for patients with early chronotypes whereas patients with intermediate and long chronotypes had more REM with delayed compared with normally timed sleep. Sleep onset latency, number of arousals, and time in stage N2 were less common in delayed sleep.
Patients with late chronotypes had more wakefulness in hour 1 than early chronotypes in the normal sleep time; however, all chronotypes had similar wake amounts in hours 2 to 9. For the delayed sleep opportunity, there was more wake in hour 1 than in hours 2 to 5, similar wake in hours 6 and 7 to hour 1, and wake amount in hours 8 and 9 that was greater than hour 1.
There were some limitations to this study. All chronotypes were determined using a single circadian measure, but because homeostatic processes have also been found to influence intermediate chronotypes, those based on homeostatic factors may provide differing results. Bedtime as a main effect may be a limitation of the study design, too. Participants came into both sleep opportunities with differing control in their prior sleep, which may have affected the results.
The researchers concluded that delayed sleep is beneficial for intermediate and late chronotypes prior to a night shift. “A question which remains open for early chronotypes choosing to strategically delay sleep prior to night shift is whether the positive effects of a shorter period of prior wake outweigh the negative effects of sleep loss and provide an overall improvement in night shift performance,” the authors wrote.
Reiter AM, Roach GD, Sargent C. The night before night shift: chronotype impacts total sleep and rapid eye movement sleep during a strategically delayed sleep. J Sleep Res. Published online August 10, 2022. doi:10.1111/jsr.13683