Differential regulation of circadian melatonin rhythm and sleep-wake cycle by bright lights and nonphotic time cues in humans

Jun 20, 2014American journal of physiology. Regulatory, integrative and comparative physiology

How bright light and non-light signals differently influence daily melatonin cycles and sleep-wake patterns in humans

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Abstract

Bright light exposure may enhance the effects of physical exercise on sleep-wake cycle reentrainment.

The sleep-wake cycle was fully entrained by an 8-hour phase advance in both exercise and control groups.
Physical exercise resulted in a phase advance of the circadian melatonin rhythm by an average of 6.9 hours, compared to 2.0 hours in the control group.
Exercise under bright lights improved sleep quality during the shift schedule.
Bright light exposure may strengthen the ability of the shift schedule to reset the circadian pacemaker.
Differential regulation of the sleep-wake cycle and circadian melatonin rhythm was observed, with the latter primarily influenced by bright light.

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Our previous study demonstrated that physical exercise under dim lights (<10 lux) accelerated reentrainment of the sleep-wake cycle but not the circadian melatonin rhythm to an 8-h phase-advanced sleep schedule, indicating differential effects of physical exercise on the human circadian system. The present study examined the effects of bright light (>5,000 lux) on exercise-induced acceleration of reentrainment because timed bright lights are known to reset the circadian pacemaker. Fifteen male subjects spent 12 days in temporal isolation. The sleep schedule was advanced from habitual sleep times by 8 h for 4 days, which was followed by a free-run session. In the shift session, bright lights were given during the waking time. Subjects in the exercise group performed 2-h bicycle running twice a day. Subjects in the control kept quiet. As a result, the sleep-wake cycle was fully entrained by the shift schedule in both groups. Bright light may strengthen the resetting potency of the shift schedule. By contrast, the circadian melatonin rhythm was phase-advanced by 6.9 h on average in the exercise group but only by 2.0 h in the control. Thus physical exercise prevented otherwise unavoidable internal desynchronization. Polysomnographical analyses revealed that deterioration of sleep quality by shift schedule was protected by physical exercise under bright lights. These findings indicate differential regulation of sleep-wake cycle and circadian melatonin rhythm by physical exercise in humans. The melatonin rhythm is regulated primarily by bright lights, whereas the sleep-wake cycle is by nonphotic time cues, such as physical exercise and shift schedule.

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Differential regulation of circadian melatonin rhythm and sleep-wake cycle by bright lights and nonphotic time cues in humans

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