After a series of night shifts, 30% of police officers adapted to a night-oriented schedule based on .
Before shifts, 60%-89% of officers were adapted to a day schedule based on aMT6 rhythms.
71%-78% of officers were adapted to a day schedule based on rhythms before shifts.
Officers who adapted to night shifts experienced significantly larger phase-delay shifts in aMT6s (-7.3 ± 0.9 h) and cortisol (-6.3 ± 0.8 h) compared to non-adapted officers.
A large proportion of police officers remained in a state of circadian misalignment after working night shifts.
Simplified
Misalignment of behavior and circadian rhythms due to night work can impair sleep and waking function. While both simulated and field-based studies suggest that circadian adaptation to a nocturnal schedule is slow, the rates of adaptation in real-world shift-work conditions are still largely unknown. The aim of this study was to evaluate the extent of adaptation of 24-h rhythms with (aMT6s) and in police officers working rotating shifts, with a special attention to night shifts. A total of 76 police officers (20 women; aged 32 ± 5.4 years, mean ± SD) from the province of Quebec, Canada, participated in a field study during their 28- or 35-day work cycle. Urine samples were collected for ~32 h before a series of day, evening, and night shifts to assess circadian phase. Before day, evening, and night shifts, 60%-89% of officers were adapted to a day schedule based on aMT6 rhythms, and 71%-78% were adapted based on cortisol rhythms. To further quantify the rate of circadian adaptation to night shifts, initial and final phases were determined in a subset of 37 officers with suitable rhythms for both hormones before and after 3-8 consecutive shifts (median = 7). Data were analyzed with circular and linear mixed-effects models. After night shifts, 30% and 24% of officers were adapted to a night-oriented schedule for aMT6s and cortisol, respectively. Significantly larger phase-delay shifts (aMT6s: -7.3 ± 0.9 h; cortisol: -6.3 ± 0.8 h) were observed in police officers who adapted to night shifts than in non-adapted officers (aMT6s: 0.8 ± 0.9 h; cortisol: 0.2 ± 1.1 h). Consistent with prior research, our results from both urinary aMT6s and cortisol midpoints indicate that a large proportion of police officers remained in a state of circadian misalignment following a series of night shifts in dim-light working environments.
Key numbers
30%
Adaptation Rate for
Percentage of officers whose rhythms adapted to night shifts.
24%
Adaptation Rate for
Percentage of officers whose rhythms adapted to night shifts.
6.4 h vs. 5.8 h
Cumulative Sleep Difference
Average cumulative sleep per day for adapted vs. non-adapted officers during night shifts.
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Conflict Of Interest StatementD.B.B. provides consultation services and legal expert advice on shift-work and sleep-related topics. Other authors have no conflicts of interest to declare.
