A week of simulated night work delays salivary melatonin onset.

By night 7 of simulated night shifts, there was a mean cumulative phase delay of 5.5 hours.

• Salivary dim light melatonin onset (DLMO) was used as an alternative marker for circadian phase.
• The night work schedule resulted in a phase delay, observed as later DLMO times.
• The average phase delay was approximately 0.8 hours per day over the course of the study.
• Exposure to natural light may inhibit the phase delay associated with night work.
• Partial circadian adaptation occurred in response to the simulated night work schedule.

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