Controlling light–dark exposure patterns rather than sleep schedules determines circadian phase (original) (raw)
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Sleep, 2011
To evaluate the effect of increasing the intensity and/or duration of exposure on light-induced changes in the timing of the circadian clock of humans. Multifactorial randomized controlled trial, between and within subject design General Clinical Research Center (GCRC) of an academic medical center 56 healthy young subjects (20-40 years of age) Research subjects were admitted for 2 independent stays of 4 nights/3 days for treatment with bright or dim-light (randomized order) at a time known to induce phase delays in circadian timing. The intensity and duration of the bright light were determined by random assignment to one of 9 treatment conditions (duration of 1, 2, or 3 hours at 2000, 4000, or 8000 lux). Treatment-induced changes in the dim light melatonin onset (DLMO) and dim light melatonin offset (DLMOff) were measured from blood samples collected every 20-30 min throughout baseline and post-treatment nights. Comparison by multi-factor analysis of variance (ANOVA) of light-indu...
Journal of circadian rhythms, 2005
Our aims were to examine the influence of different bright light schedules on mood, sleep, and circadian organization in older adults (n = 60, ages 60-79 years) with insomnia and/or depression, contrasting with responses of young, healthy controls (n = 30, ages 20-40 years). Volunteers were assessed for one week in their home environments. Urine was collected over two 24-hour periods to establish baseline acrophase of 6-sulphatoxymelatonin (aMT6s) excretion. Immediately following home recording, volunteers spent five nights and four days in the laboratory. Sleep periods were fixed at eight hours in darkness, consistent with the volunteers' usual sleep periods. Volunteers were randomly assigned to one of three light treatments (four hours per day) within the wake period: (A) two hours of 3,000 lux at 1-3 hours and 13-15 hours after arising; (B) four hours of 3,000 lux at 6-10 hours after arising; (C) four hours of dim placebo light at 6-10 hours after arising. Lighting was 50 lux...
The effects of shifting sleep two hours within a fixed photoperiod
Journal of Neural Transmission, 1991
This study examined the effects of shifting the time of sleep within a constant photoperiod on the circadian rhythms of body temperature and melatonin secretion. Subjects lived under conditions of a long scotoperiod (dim light of less than 10 lux from 6p.m. until 8 a.m.) for three weeks. In order to delineate dawn and dusk, subjects received one hour of bright light (2500 lux) before and after the scotoperiod (i.e., from 8 to 9 a.m. and from 5 to 6 p.m.). For the first week of the experiment they slept from 10 p.m. until 6 a.m. In the second week, sleep was advanced two hours; that is, subjects retired at 8 p.m. and arose at 4 a.m. The third week was a repeat of the first, resulting in a twohour delay of sleep from week two to three. The six subjects who successfully completed this protocol had no significant changes in the timing of the body temperature minima and onset of secretion of melatonin. This indicates that the timing of allowed sleep has less of an immediate effect on circadian rhythms than the timing of the external light-dark cycle. The circadian effects of the timing of sleep may be due more to the light-dark cycle that is imposed by the sleep-wake cycle than from the timing of sleep itself.
Scientific Reports
Human cognitive functioning shows circadian variations throughout the day. However, individuals largely differ in their timing during the day of when they are more capable of performing specific tasks and when they prefer to sleep. These interindividual differences in preferred temporal organization of sleep and daytime activities define the chronotype. Since a late chronotype is associated with adverse mental and physical consequences, it is of vital importance to study how lighting environments affect chronotype. Here, we use a mathematical model of the human circadian pacemaker to understand how light in the built environment changes the chronotype distribution in the population. In line with experimental findings, we show that when individuals spend their days in relatively dim light conditions, this not only results in a later phase of their biological clock but also increases interindividual differences in circadian phase angle of entrainment and preferred sleep timing. Increa...
The Journal of physiology, 2018
Shift work is highly prevalent and is associated with significant adverse health impacts. There is substantial inter-individual variability in the way the circadian clock responds to changing shift cycles. The mechanisms underlying this variability are not well understood. We tested the hypothesis that light-dark exposure is a significant contributor to this variability; when combined with diurnal preference, the relative timing of light exposure accounted for 71% of individual variability in circadian phase response to night shift work. These results will drive development of personalised approaches to manage circadian disruption among shift workers and other vulnerable populations to potentially reduce the increased risk of disease in these populations. Night shift workers show highly variable rates of circadian adaptation. This study examined the relationship between light exposure patterns and the magnitude of circadian phase resetting in response to night shift work. In 21 part...
American Journal of Physiology-Endocrinology and Metabolism, 2001
We tested the hypothesis that circadian adaptation to night work is best achieved by combining bright light during the night shift and scheduled sleep in darkness. Fifty-four subjects participated in a shift work simulation of 4 day and 3 night shifts followed by a 38-h constant routine (CR). Subjects received 2,500 lux ( Bright Light) or 150 lux ( Room Light) during night shifts and were scheduled to sleep (at home in darkened bedrooms) from 0800 to 1600 ( Fixed Sleep) or ad libitum ( Free Sleep). Dim light melatonin onset (DLMO) was measured before and after the night shifts. Both Fixed Sleepand Bright Light conditions significantly phase delayed DLMO. Treatments combined additively, with light leading to larger phase shifts. Free Sleep subjects who spontaneously adopted consistent sleep schedules adapted better than those who did not. Neither properly timed bright light nor fixed sleep schedules were consistently sufficient to shift the melatonin rhythm completely into the sleep ...
Circadian phase response curves to light in older and young women and men
Journal of Circadian Rhythms, 2007
The phase of a circadian rhythm reflects where the peak and the trough occur, for example, the peak and trough of performance within the 24 h. Light exposure can shift this phase. More extensive knowledge of the human circadian phase response to light is needed to guide light treatment for shiftworkers, air travelers, and people with circadian rhythm phase disorders. This study tested the hypotheses that older adults have absent or weaker phase-shift responses to light (3000 lux), and that women's responses might differ from those of men.
Journal of Pineal Research, 1994
Different patterns of light exposure in relation to melatonin and cortisol rhythms and sleep of night workers. J. Pineal Res. 1994:16:127-135. Abstract: There is strong evidence to suggest that circadian psychophysiological adaptation processes are modified by light, depending on its intensity and timing. To characterize such modifications and determine whether they are associated with an alteration in the dayhight pattern of melatonin excretion, measurements were obtained around the clock in 14 permanent night workers, each studied over a 48 hr period in the field. The light exposure behavior of these workers was studied with a newly developed light dosimetry by measuring light intensity at eye level. Physical activity was continuously registered and sleep indices were obtained by sleep logs and activity markings. Circadian rhythms of melatonin and cortisol were analysed from salivary samples collected for 24 hr at 2 hr intervals. The interindividual variation of melatonin acrophase determined by cosinor analysis was greater than 180 degrees (from around midnight to noon) and that of cortisol was about 135 degrees (from early morning to afternoon). Hormonal phase positions coincided significantly with light exposure: the more bright light pulses in the morning (maximum lux between 0600 and 0900), the less were the melatonin and cortisol acrophases shifted into the day. There was also a negative correlation between melatonin acrophase shift and duration of the overall light exposure above 1500 lux. Morning light maximum and sleep onset correlated highly significantly. Night workers were divided into those with less than ('non-shifters', n = 9) and more than 6 hr deviation from midnight ('shifters', n = 5) of the melatonin acrophase. The group comparison revealed a marked difference of the mean melatonin concentrations at night, and at 0700. Shifters did not experience bright light exposure in the morning and showed a tendency towards shorter overall exposure of light above 1500 lux. In conclusion, light avoidance behavior during morning hours, as observed in 5 out of 14 night workers, coincided significantly with a phase delay of melatonin acrophase. Light avoidance also correlated with an earlier sleep onset and a tendency to longer sleep hours. Thus our data suggest that the interaction of a phase shifted activity cycle and the lighvdark exposure leads in the field situation to different degrees of adaptation to the prevailing activitykest requirements, depending on dose and phase position of bright light exposure.
Behavioral Sleep Medicine, 2003
The endogenous melatonin onset in dim light (DLMO) is a marker of circadian phase that can be used to appropriately time the administration of bright light or exogenous melatonin in order to elicit a desired phase shift. Determining an individual's circadian phase can be costly and time-consuming. We examined the relationship between the DLMO and sleep times in 16 young healthy individuals who slept at their habitual times for a week. The DLMO occurred about 2 hours before bedtime and 14 hours after wake. Wake time and midpoint of sleep were significantly associated with the DLMO (r = 0.77, r = 0.68 respectively), but bedtime was not (r = 0.36). The possibility of predicting young healthy normally entrained people's DLMOs from their sleep times is discussed.