There are three mechanisms that may contribute to the health, performance, and safety problems associated with night-shift work: (1) circadian misalignment between the internal circadian clock and ...activities such as work, sleep, and eating, (2) chronic, partial sleep deprivation, and (3) melatonin suppression by light at night. The typical countermeasures, such as caffeine, naps, and melatonin (for its sleep-promoting effect), along with education about sleep and circadian rhythms, are the components of most fatigue risk-management plans. We contend that these, while better than nothing, are not enough because they do not address the underlying cause of the problems, which is circadian misalignment. We explain how to reset (phase-shift) the circadian clock to partially align with the night-work, day-sleep schedule, and thus reduce circadian misalignment while preserving sleep and functioning on days off. This involves controlling light and dark using outdoor light exposure, sunglasses, sleep in the dark, and a little bright light during night work. We present a diagram of a sleep-and-light schedule to reduce circadian misalignment in permanent night work, or a rotation between evenings and nights, and give practical advice on how to implement this type of plan.
Night shift work and rapid transmeridian travel result in a misalignment between circadian rhythms and the new times for sleep, wake, and work, which has health and safety implications for both the ...individual involved and the general public. Entrainment to the new sleep/wake schedule requires circadian rhythms to be phase-shifted, but this is often slow or impeded. The authors show superimposed light and melatonin PRCs to explain how to appropriately time these zeitgebers to promote circadian adaptation. They review studies in which bright light and melatonin were administered to try to counteract jet lag or to produce circadian adaptation to night work. They demonstrate how jet lag could be prevented entirely if rhythms are shifted before the flight using their preflight plan and discuss the combination of interventions that they now recommend for night shift workers.
Summary
The time at which the dim light melatonin onset (DLMO) occurs can be used to ensure the correct timing of light and/or melatonin administration in order to produce desired circadian phase ...shifts. Sometimes however, measuring the DLMO is not feasible. Here we determined if the DLMO was best estimated from fixed sleep times (based on habitual sleep times) or free (ad libitum) sleep times. Young healthy sleepers on fixed (n = 60) or free (n = 60) sleep schedules slept at home for 6 days. Sleep times were recorded with sleep logs verified with wrist actigraphy. Half‐hourly saliva samples were then collected during a dim light phase assessment and were later assayed to determine the DLMO. We found that the DLMO was more highly correlated with sleep times in the free sleepers than in the fixed sleepers (DLMO versus wake time, r = 0.70 and r = 0.44, both P < 0.05). The regression equation between wake time and the DLMO in the free sleepers predicted the DLMO in an independent sample of free sleepers (n = 23) to within 1.5 h of the actual DLMO in 96% of cases. These results indicate that the DLMO can be readily estimated in people whose sleep times are minimally affected by work, class and family commitments. Further work is necessary to determine if the DLMO can be accurately estimated in people with greater work and family responsibilities that affect their sleep times, perhaps by using weekend wake times, and if this method will apply to the elderly and patients with circadian rhythm disorders.
: We investigated the impact of light exposure history on light sensitivity in humans, as assessed by the magnitude of the suppression of melatonin secretion by nocturnal light. The hypothesis was ...that following a week of increased daytime bright‐light exposure, subjects would become less sensitive to light, and that after a week of restriction to dimmer light they would become more sensitive. During the bright week, subjects (n = 12) obtained 4.3 ± 0.4 hr of bright light per day (by going outside and using light boxes indoors). During the dim week, they wore dark goggles (about 2% light transmission) when outside during daylight and spent 1.4 ± 0.9 hr per day outside. Saliva samples were obtained every 30 min for 7 hr in dim light (<15 lux) on two consecutive nights (baseline and test night) at the end of each week. On the test night, 500 lux was presented for 3 hr in the middle of the collection period to suppress melatonin. There was significantly more suppression after the dim week compared with after the bright week (to 53 versus 41% of the baseline night values, P < 0.05). However, there were large individual differences, and the difference between the bright and dim weeks was most pronounced in seven of the 12 subjects. Possible reasons for these individual differences are discussed, including the possibility that 1 wk was not long enough to change light sensitivity in some subjects. In conclusion, this study suggests that the circadian system's sensitivity to light can be affected by a recent change in light history.
Context: Both light and melatonin can be used to phase shift the human circadian clock, but the phase-advancing effect of the combination has not been extensively investigated.
Objective: The ...objective of the study was to determine whether phase advances induced by morning intermittent bright light and a gradually advancing sleep schedule could be increased with afternoon melatonin.
Participants: Healthy adults (25 males, 19 females, between the ages of 19 and 45 yr) participated in the study.
Design: There were 3 d of a gradually advancing sleep/dark period (wake time 1 h earlier each morning), bright light on awakening four 30-min bright-light pulses (∼5000 lux) alternating with 30 min room light < 60 lux and afternoon melatonin, either 0.5 or 3.0 mg melatonin timed to induce maximal phase advances, or matching placebo. The dim light melatonin onset was measured before and after the treatment to determine the phase advance.
Results: There were significantly larger phase advances with 0.5 mg (2.5 h, n = 16) and 3.0 mg melatonin (2.6 h, n = 13), compared with placebo (1.7 h, n = 15), but there was no difference between the two melatonin doses. Subjects did not experience jet lag-type symptoms during the 3-d treatment
Conclusions: Afternoon melatonin, morning intermittent bright light, and a gradually advancing sleep schedule advanced circadian rhythms almost 1 h/d and thus produced very little circadian misalignment. This treatment could be used in any situation in which people need to phase advance their circadian clock, such as before eastward jet travel or for delayed sleep phase syndrome.
Abstract
Introduction:
Approximately 85% of American teens experience chronic sleep restriction due in part to a dissonance between delayed circadian timing and early school start times. Morning ...bright light advances circadian timing and may be used to increase sleep duration on school-nights; however, the most effective light duration to advance rhythms remains unknown in this age group. The purpose of this study was to quantify phase advances in response to two durations of morning bright light in teenagers.
Methods:
Thirty-seven adolescents (16.41 ± 1.04 years; 21 females) slept unrestricted at home for 3 weeks before living in the lab for a weekend. On Friday evening, participants completed a baseline dim light melatonin onset (DLMO) assessment. Salivary melatonin samples were collected in 30-min intervals in dim light (<5 lux). Participants received 1.5h bright light (n=11; ~6,000 lux; three 30-min exposures), 2.5h bright light (n=13; three 50-min exposures) or room light (~100 lux; control group; n=13) upon waking on Saturday and Sunday mornings. Bright light started 1h after weekend midsleep time (MST) on Saturday and at weekend MST on Sunday. The sleep/dark episode advanced on Saturday night. A final DLMO was measured on Sunday evening. Phase shifts were the difference between baseline and final DLMO.
Results:
Room light, 1.5h, and 2.5h of bright light resulted in 0.56 ± 0.40h, 0.66 ± 0.53h, and 1.04 ± 0.44h phase advances, respectively (between group effect: (F(2,34)=4.14, p=0.03). Post-hoc analyses revealed that 2.5h bright light produced greater phase shifts than both 1.5h bright light (p=0.04) and room light (p=0.01). 1.5h of bright light did not produce larger phase shifts than room light (p=0.60).
Conclusion:
Findings demonstrate that 2.5h of bright light on two weekend mornings, is necessary to advance circadian rhythms of teens by 1h, and 1.5h of morning bright light was no more effective than room light when timed to begin just after weekend MST. Our adolescent phase response curve to light predicts maximum phase advances 2-6h after MST, which may explain why the longer stimulus produced the largest phase shift. These findings inform methods to phase advance teenagers to facilitate earlier sleep onset and increase school-night sleep duration.
Support (If Any):
R01HL223756(SJC).
Abstract
Introduction:
Racial differences exist in sleep duration and circadian timing, however it is unknown whether these differences extend to cognitive performance. The current study investigated ...the role of ancestry on sleep and performance before and after a 9h advance of the sleep/wake episode.
Methods:
Twenty African-Americans (9F; 32.1 ± 7.5yr) and 17 European-Americans (8F; 29.7 ± 5.7yr) completed the study. Participants were scheduled to four baseline days each with 8h time in bed based on their habitual sleep schedule such that sleep and circadian rhythms were aligned. The sleep-wake schedule was then advanced 9h earlier (misaligned) for three days. Total sleep time (TST) was assessed with actigraphy. The Automated Neuropsychological Assessment Metrics (ANAM) test battery was administered every 3h each day starting 2h after waking. Tests included a simple reaction time task (SRT) and Stanford sleepiness scale (SSS). Mixed model ANOVAs assessed the effects of ancestry (African-American or European-American) and condition (aligned or misaligned) on sleep and performance.
Results:
TST was reduced on misaligned days compared to baseline (F=18.67, p<0.001) and African-Americans slept less compared to European-Americans (F=8.58, p<0.01), especially on the first two misaligned days when the difference was 47 and 59 minutes respectively (F=6.67, p<0.01). Compared to baseline, misalignment increased SSS ratings (F=72.69, p<0.001), but did not affect the number of lapses (F=0.02, p=0.90) or median reaction time (RT)(F=0.02, p=0.88) on the SRT. While there was no effect of ancestry on SSS (F=0.22, p=0.64), there was a trend for lapses (F=3.55, p=0.07) and median RT (F=2.80, p=0.10) to be higher for African-Americans. On misaligned days, African-Americans performed worse than European-Americans at times corresponding to the end of baseline sleep (lapses, F=7.16, p<0.05; median RT, F=5.16, p<0.05).
Conclusion:
Racial disparities in sleep may be more prominent when the sleep episode is shifted, and there may be racial differences in the circadian regulation of performance. Results have implications for the sleep and performance of individuals undertaking shiftwork or transmeridan travel.
Support (If Any):
R01NR007677(CIE).
Abstract
Introduction:
We conducted two studies that were similar for the first 10 days (nature.com/articles/srep08381, nature.com/articles/srep36716), and determined each subject’s ...morningness-eveningness score (MEQ), Mid-sleep on Free Days (MSF) from the MCTQ, baseline dim light melatonin onset (DLMO), phase angle of entrainment, and free-running circadian period. Ten African-Americans (6 women, 4 men) and 8 European-Americans (2 women, 6 men) participated in both studies separated by 9 to 33 months (mean ± SD = 16 ± 7). They were 32.2 ± 6.7 years old at the first study. The purpose of this report is to examine the reproducibility of these circadian variables.
Methods:
Subjects slept in the lab on a fixed 8-h sleep schedule similar to their usual sleep schedule for 4 days, followed by a circadian phase assessment with 30 min saliva samples to calculate baseline DLMO. Phase angle was the interval from DLMO to bedtime. There were also 3 days of ultradian LD cycles producing forced desynchrony. Circadian period was determined from phase assessments before and after the days of ultradian LD cycles. For each circadian variable, we made scatter plots with identical x and y axes. Lines of unity showed when the variable was exactly the same in both studies. Lines parallel to and on each side of the line of unit showed how much the variable differed between the studies. We also calculated Pearson correlations for each variable.
Results:
The MEQ score differed by less than 10 points between the two studies; MSF by 1 h or less, except for 2 subjects, baseline DLMO by 1 h or less except for 3 subjects, phase angle by 2 h or less, and circadian period by 0.3 h or less except for 2 subjects. All correlations were significant (p≤.0001), MEQ r=.85, MSF r=.78, baseline DLMO r=.81, phase angle r=.80, circadian period r=.78. A longer time between the two studies did not make the variables more different. In this small sample, there were no differences between men and women or between European and African-Americans in the stability of these variables.
Conclusion:
Circadian parameters were relatively stable over months.
Support (If Any):
NIHR01NR007677.
Abstract
Introduction:
A well-established literature demonstrates a circadian phase delay during adolescence. Despite this delay in circadian timing, adolescents must wake early for school and ...typically sleep later on weekends resulting in irregular sleep-wake timing. This analysis examined whether sleep-wake timing variability was associated with circadian phase in high-school students during the school year.
Methods:
Forty-six adolescents aged 14–17 years (16.2 ± 1.1 years; 29 females) who reported late bedtimes (>23:00 on school nights; >00:00 on non-school nights) and short school-night sleep duration (<7.5 h) completed the study. Participants slept on their usual sleep schedules for 15 days at home before a dim light melatonin onset (DLMO) assessment (light <5lux), in which saliva was sampled every 30 minutes. DLMO was the time when salivary melatonin levels exceeded 4pg/mL. Nocturnal sleep timing and duration were quantified from wrist actigraphy (11–15 nights; 14.5 ± 1.1 nights). Interquartile ranges (IQR) for sleep onset time, midsleep time, wake-up time, and sleep duration were computed and used as measures of sleep variability. Frequency of daytime naps were also examined.
Results:
Average (±SD) school-night bedtime, midsleep time, and wake time were 00:23 ± 0:56, 03:28 ± 0:34 and 06:27 ± 0:31, respectively. School-night nocturnal sleep duration averaged 6.1 ± 1.0h. Average non-school night bedtime, midsleep time, and wake time were 01:21 ± 0:58, 05:28 ± 0:54 and 09:37 ± 1:13, respectively. Weekend nocturnal sleep duration averaged 8.3 ± 1.3h. Frequency of naps ranged from 0 to 9 during the 2 weeks. On average, bedtimes were 1.0 ± 0.1h later, wake times were 3.2 ± 0.2h later, and sleep durations were 2.2 ± 0.2h longer on non-school nights compared to school nights. Variability in bedtime, midsleep time, sleep duration, and nap frequency were not associated with DLMO phase. A trend emerged for more variable wake times to be associated with later DLMOs (r=.28, p=.06).
Conclusion:
These data suggest that irregular sleep timing does not predict a later circadian phase, nor does a later circadian phase lead to more variable sleep patterns in this group of older adolescents. The only exception may be irregular wake-up times; sleeping late on weekends may be more likely in adolescents with a later circadian phase or sleeping late on weekends delays the clock.
Support (If Any):
R01HL112756 (SJC)
We studied the relationship between the phase and the amplitude of the circadian temperature rhythm using questionnaires that measure individual differences in personality variables, variables that ...relate to circadian rhythms, age and sex. The ambulatory core body temperature of 101 young men and 71 young women was recorded continuously over 6 days. The temperature minimum (Tmin) and amplitude (Tamp) were derived by fitting a complex cosine curve to each day’s data for each subject. Participants completed the Horne–Ostberg Morningness–Eveningness Questionnaire (MEQ), the Circadian Type Inventory (CTI) and the MMPI‐2, scored for the Psychopathology‐5 (PSY‐5) personality variables. We found that the average Tmin occurred at 03.50 h for morning‐types (M‐types), 05.02 h for the neither‐types and 06.01 h for evening‐types (E‐types). Figures were presented that could provide an estimate of Tmin given an individual’s morningness–eveningness score or weekend wake time. The Tmin occurred at approximately the middle of the 8‐h sleep period, but it occurred closer to wake in subjects with later Tmin values and increasing eveningness. In other words, E‐types slept on an earlier part of their temperature cycle than M‐types. This difference in the phase‐relationship between temperature and sleep may explain why E‐types are more alert at bedtime and sleepier after waking than M‐types. The Tmin occurred about a half‐hour later for men than women. Another interesting finding included an association between circadian rhythm temperature phase and amplitude, in that subjects with more delayed phases had larger amplitudes. The greater amplitude was due to lower nocturnal temperature.
PDF
