Human circadian melatonin rhythm phase delay during a fixed sleep–wake schedule interspersed with nights of sleep deprivation

Aug 23, 2003Journal of pineal research

Delays in the daily melatonin cycle during a fixed sleep schedule with occasional all-nighters

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Abstract

The phase of the human circadian pacemaker can be delayed by an average of 1.4 hours after one night of sleep deprivation in dim light.

Low levels of light exposure (0.03 lux) during sleep and moderate levels (5-13 lux) during wakefulness were used to study circadian phase stability.
The phase of melatonin rhythm was observed to shift to a later time after sleep deprivation, indicating potential instability of the circadian pacemaker under certain conditions.
Subjects with low amplitude melatonin rhythms experienced the largest delays in melatonin onset.
Sleep deprivation in a supine body posture resulted in a significant reduction in melatonin secretion compared to other conditions, suggesting posture may influence melatonin levels.
The overall phase position of melatonin profiles was not significantly affected by differences in body posture during the study.

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The human circadian pacemaker, with an intrinsic period between 23.9 and 24.5 hr, can be reset by low levels of light. Biomathematical models of the human clock predict that light-dark cycles consisting of only approximately 3.5 lux during 16 hr of wakefulness and 0 lux during 8 hr of sleep should entrain approximately 45% of the population. However, under real-life conditions, sleep-wake schedules and the associated light-dark exposures are often irregular. It remains unclear whether the phase of the pacemaker would remain stable under such conditions. We investigated the stability of the circadian phase in dim light by assessing the plasma melatonin rhythm during nine consecutive circadian cycles. Ten subjects were scheduled to sleep for 8 hr (0.03 lux) and to be awake for 16 hr (5-13 lux) during all days except on days 4 and 8, during which the subjects were sleep deprived for 40 hr (5-13 lux), either in a sitting/standing or supine body posture. In all subjects, the phase of the melatonin rhythm occurred at a later clock time on day 9 than on day 2 (average delay: 1.4 hr). Largest delays in the melatonin onset were observed in subjects with low amplitude melatonin rhythms. The area under the curve during active melatonin secretion was significantly reduced when subjects were sleep deprived in the 40-hr supine body posture condition compared with either the 40-hr sitting/standing sleep deprivation (SD) or the ambulatory condition under non-SD conditions. Posture differences did not significantly affect the relative phase position of the melatonin profiles. The data indicate that under conditions of reduced zeitgeber strength, the phase of the human circadian pacemaker, using plasma melatonin as a marker, can be phase delayed by one night of SD and the associated dim light exposure.

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Human circadian melatonin rhythm phase delay during a fixed sleep–wake schedule interspersed with nights of sleep deprivation

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