Effects of timing of shifts on sleepiness and sleep duration.

This review summarizes the effects on sleep duration and sleepiness of (1) the timing of shifts (start and finishing times) and (2) the scheduling of free time between shifts. The results from the few studies available show that sleep duration is clearly determined by the change over time between the night and the morning shift-no more than 5 or 6 hours of sleep is obtained before the morning shift if the shift starts at 06.00 hours or earlier. Therefore, it is suggested that the morning shift should not start before 07.00 hours. A late start of the morning shift will however, increase the sleepiness at the end of the night shift, as well as decrease the duration of the daysleep after the night shift. On the other hand, one may argue that the short daysleep after a night shift may be compensated for by an evening nap, whereas a short night sleep before a morning shift cannot (no time for nap). The review of studies concerning free time between shifts suggests that at least 16 hours is needed and that quick change-overs should be avoided. The free time after a spell of night shifts should be at least 48 hours since the shiftworker needs two main sleep episodes to recover from night work.