Association between melatonin secretion and daytime sleep complaints in night nurses

To test the hypothesis that nightworkers' diurnal sleep complaints are associated with the timing of melatonin secretion.

After a minimum of three consecutive night shifts, the subjects were admitted to the laboratory for 24 hours during which they were allowed to eat and sleep ad lib. Urine was collected every two hours under dim illumination (<25 lux). Concentration of urinary 6-sulphatoxymelatonin (UaMT6s) was determined by radioimmunoassay. Sleep quality was assessed by questionnaires.

NA PARTICIPANTS: Two groups of 15 night nurses with mild and severe daytime sleep complaints.

NA RESULTS: The proportion of the episode of UaMT6s excretion happening during the day (between 08:00 and 00:00 hours) was smaller in the group of nightworkers with severe daytime sleep complaints, and was negatively correlated with the severity of the complaints over the 30 subjects. A longer duration of melatonin secretion was associated with a lower severity of daytime sleep complaints. However, in most of the subjects with good daytime sleep quality, melatonin secretion remained essentially nocturnal, and the overlap with the time of their sleep episode was small or even absent.

Timing and duration of melatonin secretion were associated with better daytime sleep quality when the subjects had an increased proportion of melatonin secreted during the day. When there was an indication of circadian phase shift, the direction of the shift was not of primary importance for daytime sleep quality. A longer duration of melatonin secretion may increase the tolerance to an abnormal circadian phase.