Differential regulation of circadian melatonin rhythm and sleep-wake cycle by bright lights and nonphotic time cues in humans (original) (raw)
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Daily exercise facilitates phase delays of circadian melatonin rhythm in very dim light
AJP: Regulatory, Integrative and Comparative Physiology, 2004
Daily exercise facilitates phase delays of circadian melatonin rhythm in very dim light. Shift workers and transmeridian travelers are exposed to abnormal work-rest cycles, inducing a change in the phase relationship between the sleep-wake cycle and the endogenous circadian timing system. Misalignment of circadian phase is associated with sleep disruption and deterioration of alertness and cognitive performance. Exercise has been investigated as a behavioral countermeasure to facilitate circadian adaptation. In contrast to previous studies where results might have been confounded by ambient light exposure, this investigation was conducted under strictly controlled very dim light (standing ϳ0.65 lux; angle of gaze) conditions to minimize the phase-resetting effects of light. Eighteen young, fit males completed a 15-day randomized clinical trial in which circadian phase was measured in a constant routine before and after exposure to a week of nightly bouts of exercise or a nonexercise control condition after a 9-h delay in the sleep-wake schedule. Plasma samples collected every 30 -60 min were analyzed for melatonin to determine circadian phase. Subjects who completed three 45-min bouts of cycle ergometry each night showed a significantly greater shift in the dim light melatonin onset (DLMO 25%), dim light melatonin offset, and midpoint of the melatonin profile compared with nonexercising controls (Student t-test; P Ͻ 0.05). The magnitude of phase delay induced by the exercise intervention was significantly dependent on the relative timing of the exercise after the preintervention DLMO 25% (r ϭ Ϫ0.73, P Ͻ 0.05) such that the closer to the DLMO 25%, the greater the phase shift. These data suggest that exercise may help to facilitate circadian adaptation to schedules requiring a delay in the sleep-wake cycle. circadian; jet lag; shift work SCHEDULED PHYSICAL ACTIVITY such as wheel running in rodents and exercise in humans has been reported to influence the circadian timing system. Wheel running (12, 31) and forced treadmill running (21, 24) have been reported to entrain circadian rhythms in hamsters (31) and mice (12, 21) and when the period of the free-running rhythm was close to the period of the treadmill schedule in rats (24). Several studies have assessed the effectiveness of exercise as a circadian phase-resetting agent in humans. Van Reeth et al. (34) reported that a single exercise bout, centered from 3 h before to 2 h after the body temperature minimum, phase delayed the human circadian rhythms of temperature and thyrotropin. In that study, exercise that consisted of 3 h of alternating arm and leg ergometry at 40 and 60% of maximal O 2 consumption (V O 2 max ) was performed under constant lighting conditions of Ͻ300 lux. Using the same protocol, Baehr and colleagues (1) reported similar phase delays between young and older adults. Another study reported that higher-intensity exercise of shorter duration, 1 h of stair climbing at 75% V O 2 max , centered at 0100 (in ϳ70 -80 lux), also elicited significant phase delays in the circadian rhythm of thyrotropin. Recently, this protocol was expanded to include scheduled morning, afternoon, evening, and night exercise sessions in ϳ40 lux (8). Significant phase delays were reported for noctural exercise, and significant phase advances were reported for evening exercise. Only one other study to date has reported that exercise can advance the human circadian pacemaker. In a shortened T-cycle protocol of twelve 23-h and 40-min cycles, subjects who performed two bouts of cycling and rowing at a heart rate of 140 beats/min during the morning and afternoon showed a 1.6-h advance in the peak of the plasma melatonin rhythm, whereas subjects in the nonexercise control condition averaged a 0.80-h phase delay of the melatonin peak (25).
AJP: Regulatory, Integrative and Comparative Physiology, 2010
Effects of timed physical exercise were examined on the reentrainment of sleep-wake cycle and circadian rhythms to an 8-h phase-advanced sleep schedule. Seventeen male adults spent 12 days in a temporal isolation facility with dim light conditions (<10 lux). The sleep schedule was phase-advanced by 8 h from their habitual sleep times for 4 days, which was followed by a free-run session for 6 days, during which the subjects were deprived of time cues. During the shift schedule, the exercise group ( n = 9) performed physical exercise with a bicycle ergometer in the early and middle waking period for 2 h each. The control group ( n = 8) sat on a chair at those times. Their sleep-wake cycles were monitored every day by polysomnography and/or weight sensor equipped with a bed. The circadian rhythm in plasma melatonin was measured on the baseline day before phase shift: on the 4th day of shift schedule and the 5th day of free-run. As a result, the sleep-onset on the first day of free-r...
Phase-adjustment of human circadian rhythms by light and physical exercise
The Journal of Physical Fitness and Sports Medicine
The human circadian system derives from two distinct circadian oscillators that separately regulate circadian rhythms of body temperature and plasma melatonin, and of the sleep-wake cycle. The oscillator for body temperature and melatonin is the central circadian pacemaker, located in the hypothalamic suprachiasmatic nucleus (SCN), and the oscillator for sleep-wake cycle is another oscillator, located in the brain but outside the SCN. Although bright light is a primary zeitgeber for circadian rhythms, non-photic time cues such as a strict sleep schedule and timed physical exercise act as a non-photic zeitgeber for the sleep-wake cycle under dim light conditions, independent on the SCN circadian pacemaker. Recently, timed physical exercise under bright light has been shown to accelerate re-entrainment of circadian rhythms to an advanced sleep schedule. Physical exercise may enhance the phase-shift of circadian rhythm caused by bright light by changing light perception. In the field of sports medicine and exercise science, adjustment of the circadian rhythm is important to enable elite athletes to take a good sleep and enhance exercise performance, especially after inter-continental travel and jet lag.
Circadian phase-delaying effects of bright light alone and combined with exercise in humans
American journal of physiology. Regulatory, integrative and comparative physiology, 2002
In a within-subjects (n = 18), counterbalanced design, the circadian phase-shifting effects of 3 h of 1) bright light (3,000 lx) alone 2) and bright light combined with vigorous exercise were compared. For each treatment, volunteers spent 3 nights and 2 days in the laboratory, typically receiving the treatment from approximately 2300 to 0200 on night 2. Bedtimes and waketimes were fixed to the volunteers' habits. Illumination was 50 lx during other wake hours and 0 lx during sleep. Bright Light Alone elicited a significant phase delay in rectal temperature minimum (70 min), but not in urinary 6-sulphatoxymelatonin (6-SMT) acrophase (20 min). Bright Light + Exercise elicited a significant phase delay in 6-SMT (68 min), but did not result in a significant difference in shift compared with Bright Light Alone. The study had adequate statistical power (80%) to detect phase-shift differences between treatments of approximately 2-2.5 h. Thus any antagonism of light shifts with exercise...
Effects of physical exercise on human circadian rhythms
Sleep and Biological Rhythms, 2006
Bright light is the principal zeitgeber for the biological clock in mammals, including humans. But there is a line of evidence that non-photic stimuli such as physical activity play an important role in entrainment. Scheduled physical activity, such as wheel and forced treadmill running, has been reported to phase-shift and entrain the circadian rhythm in rodent species. In humans, several studies have reported the phase-shifting effects of physical exercise. A single bout of physical exercise at night was demonstrated to phase-delay the circadian rhythm in plasma melatonin. However, for the entrainment of human circadian rhythm, a phase-advance shift is needed. Previously, we demonstrated that scheduled physical exercise in the waking period facilitated the entrainment of plasma melatonin rhythm to the sleep/wake schedule of 23 h 40 min. This result suggested that timed physical exercise produced phase-advance shifts. A regular physical exercise also facilitated entrainment of the circadian rhythms associated with acute phase-delay shifts of the sleep/wake and light/dark schedule. These findings suggest that physical exercise is useful to adjust the circadian rhythm to external time cues, especially for totally blind people and elderly people.
Resetting the Melatonin Rhythm with Light in Humans
Journal of Biological Rhythms, 1997
The endogenous circadian rhythm of melatonin in humans provides information regarding the resetting response of the human circadian timing system to changes in the light-dark (LD) cycle. Alterations in the LD cycle have both acute and chronic effects on the observed melatonin rhythm. Investigations to date have firmly established that the melatonin rhythm can be reentrained following an inversion of the LD cycle. Exposure to bright light and darkness given over a series of days can rapidly induce large-magnitude phase shifts of the melatonin rhythm. Even single pulses of bright light can shift the timing of the melatonin rhythm. Recent data have demonstrated that lower light intensities than originally believed are capable of resetting the melatonin rhythm and that stimulation of photopically sensitive photoreceptors (i.e., cones) is sufficient to reset the endogenous circadian melatonin rhythm. In addition to phase resetting, exposure to light of critical timing, strength, and dura...
Non-photic entrainment of human rest-activity cycle independent of circadian pacemaker
Sleep and Biological Rhythms, 2004
Entrainment of rest-activity cycles and plasma melatonin rhythms by a forced schedule was examined in humans who were held in temporal isolation with dim light conditions (< 10 lx). The sleep schedule of subjects was phase-advanced by approximately 8 h from the habitual sleep time for 8 days, which was followed by a free-running session where the subjects self-determined the times of sleep and wake up for 6 days. As a result, the rest-activity cycle was advanced by 8.2 h on the first day of free-run after the forced schedule, whereas the circadian melatonin rhythm was not significantly shifted on the last day of the schedule. The findings indicate that the forced sleep schedule of 8 days entrain the rest-activity cycle but not the melatonin rhythm. Under free-running conditions, the rest-activity cycles resynchronized with the melatonin rhythm by either phaseadvance or phase-delay shifts. The direction and extent of phase-shift depended on the phase relationship between the rest-activity cycle and plasma melatonin rhythm one cycle before the phase-shift. The findings indicate the existence of an oscillatory coupling between the rest-activity cycle and the plasma melatonin rhythm. It is concluded that non-photic zeitgebers can entrain the rest-activity cycle in humans, which is independent of the circadian pacemaker.
The internal circadian clock and sleep-wake homeostasis regulate and organize human brain function, physiology and behavior so that wakefulness and its associated functions are optimal during the solar day and that sleep and its related functions are optimal at night. The maintenance of a normal phase relationship between the internal circadian clock, sleep-wake homeostasis and the light-dark cycle is crucial for nominal neurobehavioral and physiological function in humans. Here we show that the phase relationship between these factors -the phase angle of entrainment (ψ)-is strongly determined by the intrinsic period (τ) of the master circadian clock located in the suprachiasmatic nucleus of the hypothalamus and the strength of the circadian synchronizer. Melatonin was used as a marker of internal biological time and circadian period was estimated during a forced desynchrony protocol. We observed relationships between the phase angle of entrainment and intrinsic period after exposure to scheduled habitual wakefulness-sleep light-dark cycle conditions inside and outside of the laboratory. Individuals with shorter circadian periods initiated sleep and awakened at a later biological time than individuals with longer circadian periods. We also observed that light exposure history influenced the phase angle of entrainment such that phase angle was later following exposure to a moderate bright light (~450 lux)-dark wakefulness-sleep schedule for 5 days than exposure to a normal indoor daytime level of light (~150 lux)-dark wakefulness-sleep schedule for 2 days. These findings demonstrate that neurobiological and environmental factors interact to regulate the phase angle of entrainment in humans. This finding has important implications for understanding physiological organization by the brain's master circadian clock and may have implications for understanding mechanisms underlying circadian sleep disorders.