Rapid shift in sleep time and acrophase of melatonin secretion in short shift work schedule.

Tolerance to shift work and adaptability to shifting schedules is an issue of growing importance in industrialized society. We studied 40 registered nurses, 20 on fixed day-shifts and 20 on fixed night-shifts, to assess whether workers with rapidly shifting schedules were able to adapt their melatonin secretion and sleep-wake cycles. The day-shift worked 5 days with 2 days off and the night-shift worked 3 nights with 2 off.