Background: Sleep problems are common effects of shift work. The aim of the present study was to evaluate how different types of shift affect sleep and sleepiness, and to relate sleepiness to urinary 6-sulfatoxymelatonin.
Methods: A total of 166 volunteer healthy Danish nurses working day, evening, or night, respectively fixed and mixed schedules were included. Self-reports of sleep were assessed together with real-time sleepiness and spot urine samples analyzed for 6-sulfatoxymelatonin on a workday and a leisure day.
Results: On a day off the nurses slept longer, with a better quality and reported less sleepiness compared to a workday. Nurses on nightshift reported poorer sleep quality than nurses on other shifts. Sleepiness was highest for nurses on mixed schedules. Concentrations of urinary 6-sulfatoxymelatonin and sleepiness were generally correlated except for nurses working fixed nights.
Conclusions: The poorest sleep quality was observed for nurses in mixed schedules working nights. The lack of correlation between sleepiness and 6-sulfatoxymelatonin on mixed night shift may indicate that the influence of endogenous melatonin is limited.