SleepSep 1, 1996

Quick changes in sleep timing and peak melatonin release during short shift work schedules

Circadian Biology Weekly Brief ↗PubMed ↗

Updated Apr 1, 2026

Abstract

Night-shift workers slept significantly more on their days off compared to their workdays.

Two subgroups of night-shift nurses were identified based on their melatonin secretion patterns.
Group A, consisting of six nurses, adapted their melatonin levels effectively, aligning their acrophase with daytime on days off.
Group B, comprising 14 nurses, did not demonstrate an adaptation in melatonin secretion and had a random acrophase on workdays.
Napping at work was reported by 9 out of 20 night-shift workers, averaging 114 minutes between 3 and 6 a.m.
Total sleep time for Group A was comparable to day-shift nurses, suggesting effective adaptation.
Age may influence the ability to adapt to rapidly shifting schedules, as Group A was slightly younger and entirely female.

Simplified

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. All night-shift personnel acknowledged shifting back to daytime schedules on their days off. Sleep-wake was determined by sleep logs and actigraphy. To measure 6-sulfatoxymelatonin levels, urine was collected at 2-hour intervals on the last work day and on the last day off. Night-shift workers slept significantly more on days off. Napping on the job occurred in 9/20 night-shift workers (mean 114 minutes) between 3 and 6 a.m. The acrophase of 6-sulfatoxymelatonin in day-shift nurses occurred at similar times on workdays and off days. In night-shift nurses, the acrophase was about 7 a.m. on days off, but had a random distribution on workdays. Further analysis revealed two subgroups of night-shift nurses: six subjects (group A).demonstrated a rapid shift in melatonin secretion (acrophase at near 12 noon on work days and at near 7 a.m. on days off) while 14 nurses (group B) did not shift. Group A nurses slept more in the daytime on work days and their total sleep time was the same as day-shift nurses. Group A was slightly younger and was composed solely of women (there were nine women and five men in group B). Age may be a factor in the ability to adapt to rapidly shifting schedules.

Quick changes in sleep timing and peak melatonin release during short shift work schedules

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