Differences in Sleep,Light, and Circadian Phase in Offshore 18:00–06:00 h and 19:00–07:00 h Shift Workers

Complaints concerning sleep are high among those who work night shifts; this is in part due to the disturbed relationship between circadian phase and the timing of the sleep‐wake cycle. Shift schedule, light exposure, and age are all known to affect adaptation to the night shift. This study investigated circadian phase, sleep, and light exposure in subjects working 18:00–06:00 h and 19:00–07:00 h schedules during summer (May–August). Ten men, aged 46±10 yrs (mean±SD), worked the 19:00–07:00 h shift schedule for two or three weeks offshore (58°N). Seven men, mean age 41±12 yrs, worked the 18:00–06:00 h shift schedule for two weeks offshore (61°N). Circadian phase was assessed by calculating the peak (acrophase) of the 6‐sulphatoxymelatonin rhythm measured by radioimmunoassay of sequential urine samples collected for 72 h at the end of the night shift. Objective sleep and light exposure were assessed by actigraphy and subjective sleep diaries. Subjects working 18:00–06:00 h had a 6‐sulphatoxymelatonin acrophase of 11.7±0.77 h (mean±SEM, decimal hours), whereas it was significantly later, 14.6±0.55 h (p=0.01), for adapted subjects working 19:00–07:00 h. Two subjects did not adapt to the 19:00–07:00 h night shift (6‐sulphatoxymelatonin acrophases being 4.3±0.22 and 5.3±0.29 h). Actigraphy analysis of sleep duration showed significant differences (p=0.03), with a mean sleep duration for those working 19:00–07:00 h of 5.71±0.31 h compared to those working 18:00–06:00 h whose mean sleep duration was 6.64±0.33 h. There was a trend to higher morning light exposure (p=0.07) in the 19:00–07:00 h group. Circadian phase was later (delayed on average by 3 h) and objective sleep was shorter with the 19:00–07:00 h than the 18:00–06:00 h shift schedule. In these offshore conditions in summer, the earlier shift start and end time appears to favor daytime sleep.     

A compromise phase position for permanent night shift workers: circadian phase after two night shifts with scheduled sleep and light/dark exposure

Night shift work is associated with a myriad of health and safety risks. Phase-shifting the circadian clock such that it is more aligned with night work and day sleep is one way to attenuate these risks. However, workers will not be satisfied with complete adaptation to night work if it leaves them misaligned during days off. Therefore, the goal of this set of studies is to produce a compromise phase position in which individuals working night shifts delay their circadian clocks to a position that is more compatible with nighttime work and daytime sleep yet is not incompatible with late nighttime sleep on days off. This is the first in the set of studies describing the magnitude of circadian phase delays that occurs on progressively later days within a series of night shifts interspersed with days off. The series will be ended on various days in order to take a "snapshot" of circadian phase. In this set of studies, subjects sleep from 23:00 to 7:00 h for three weeks. Following this baseline period, there is a series of night shifts (23:00 to 07:00 h) and days off. Experimental subjects receive five 15 min intermittent bright light pulses (approximately 3500 lux; approximately 1100 microW/cm2) once per hour during the night shifts, wear sunglasses that attenuate all visible wavelengths--especially short wavelengths ("blue-blockers")--while traveling home after the shifts, and sleep in the dark (08:30-15:30 h) after each night shift. Control subjects remain in typical dim room light (<50 lux) throughout the night shift, wear sunglasses that do not attenuate as much light, and sleep whenever they want after the night shifts. Circadian phase is determined from the circadian rhythm of melatonin collected during a dim light phase assessment at the beginning and end of each study. The sleepiest time of day, approximated by the body temperature minimum (Tmin), is estimated by adding 7 h to the dim light melatonin onset. In this first study, circadian phase was measured after two night shifts and day sleep periods. The Tmin of the experimental subjects (n=11) was 04:24+/-0.8 h (mean+/-SD) at baseline and 7:36+/-1.4 h after the night shifts. Thus, after two night shifts, the Tmin had not yet delayed into the daytime sleep period, which began at 08:30 h. The Tmin of the control subjects (n=12) was 04:00+/-1.2 h at baseline and drifted to 4:36+/-1.4 h after the night shifts. Thus, two night shifts with a practical pattern of intermittent bright light, the wearing of sunglasses on the way home from night shifts, and a regular sleep period early in the daytime, phase delayed the circadian clock toward the desired compromise phase position for permanent night shift workers. Additional night shifts with bright light pulses and daytime sleep in the dark are expected to displace the sleepiest time of day into the daytime sleep period, improving both nighttime alertness and daytime sleep but not precluding adequate sleep on days off.     

Circadian phase, sleepiness, and light exposure assessment in night workers with and without shift work disorder

Most night workers are unable to adjust their circadian rhythms to the atypical hours of sleep and wake. Between 10% and 30% of shiftworkers report symptoms of excessive sleepiness and/or insomnia consistent with a diagnosis of shift work disorder (SWD). Difficulties in attaining appropriate shifts in circadian phase, in response to night work, may explain why some individuals develop SWD. In the present study, it was hypothesized that disturbances of sleep and wakefulness in shiftworkers are related to the degree of mismatch between their endogenous circadian rhythms and the night-work schedule of sleep during the day and wake activities at night. Five asymptomatic night workers (ANWs) (3 females; [mean ± SD] age: 39.2 ± 12.5 yrs; mean yrs on shift = 9.3) and five night workers meeting diagnostic criteria (International Classification of Sleep Disorders [ICSD]-2) for SWD (3 females; age: 35.6 ± 8.6 yrs; mean years on shift = 8.4) participated. All participants were admitted to the sleep center at 16:00 h, where they stayed in a dim light (<10 lux) private room for the study period of 25 consecutive hours. Saliva samples for melatonin assessment were collected at 30-min intervals. Circadian phase was determined from circadian rhythms of salivary melatonin onset (dim light melatonin onset, DLMO) calculated for each individual melatonin profile. Objective sleepiness was assessed using the multiple sleep latency test (MSLT; 13 trials, 2-h intervals starting at 17:00 h). A Mann-Whitney U test was used for evaluation of differences between groups. The DLMO in ANW group was 04:42 ± 3.25 h, whereas in the SWD group it was 20:42 ± 2.21 h (z = 2.4; p 相似文献   

Circadian Phase,Sleepiness, and Light Exposure Assessment in Night Workers With and Without Shift Work Disorder

Most night workers are unable to adjust their circadian rhythms to the atypical hours of sleep and wake. Between 10% and 30% of shiftworkers report symptoms of excessive sleepiness and/or insomnia consistent with a diagnosis of shift work disorder (SWD). Difficulties in attaining appropriate shifts in circadian phase, in response to night work, may explain why some individuals develop SWD. In the present study, it was hypothesized that disturbances of sleep and wakefulness in shiftworkers are related to the degree of mismatch between their endogenous circadian rhythms and the night-work schedule of sleep during the day and wake activities at night. Five asymptomatic night workers (ANWs) (3 females; [mean?±?SD] age: 39.2?±?12.5 yrs; mean yrs on shift?=?9.3) and five night workers meeting diagnostic criteria (International Classification of Sleep Disorders [ICSD]-2) for SWD (3 females; age: 35.6?±?8.6 yrs; mean years on shift?=?8.4) participated. All participants were admitted to the sleep center at 16:00?h, where they stayed in a dim light (<10 lux) private room for the study period of 25 consecutive hours. Saliva samples for melatonin assessment were collected at 30-min intervals. Circadian phase was determined from circadian rhythms of salivary melatonin onset (dim light melatonin onset, DLMO) calculated for each individual melatonin profile. Objective sleepiness was assessed using the multiple sleep latency test (MSLT; 13 trials, 2-h intervals starting at 17:00?h). A Mann-Whitney U test was used for evaluation of differences between groups. The DLMO in ANW group was 04:42?±?3.25?h, whereas in the SWD group it was 20:42?±?2.21?h (z = 2.4; p?<?.05). Sleep did not differ between groups, except the SWD group showed an earlier bedtime on off days from work relative to that in ANW group. The MSLT corresponding to night work time (01:00–09:00?h) was significantly shorter (3.6?±?.90?min: [M?±?SEM]) in the SWD group compared with that in ANW group (6.8?±?.93?min). DLMO was significantly correlated with insomnia severity (r = ?.68; p < .03), indicating that the workers with more severe insomnia symptoms had an earlier timing of DLMO. Finally, SWD subjects were exposed to more morning light (between 05:00 and 11:00?h) as than ANW ones (798 vs. 180 lux [M?±?SD], respectively z?=??1.7; p?<?.05). These data provide evidence of an internal physiological delay of the circadian pacemaker in asymptomatic night-shift workers. In contrast, individuals with SWD maintain a circadian phase position similar to day workers, leading to a mismatch/conflict between their endogenous rhythms and their sleep-wake schedule. (Author correspondence: vgumeny1@hfhs.org)     

Sleep parameters among offshore workers: an initial assessment in the Campos Basin, Rio De Janeiro, Brazil

Shift work has potentially adverse effects on health, particularly on sleep. The purpose of the present study was to assess sleep parameters among personnel working in oil and gas offshore installations in the Campos Basin, Rio de Janeiro, Brazil. One hundred and seventy-nine subjects were asked to complete a sleep questionnaire with multiple-choice answers. Offshore workers were divided into two groups according to their work schedule: (1) fixed daytime workers (n = 86; age: 35.8+/-9.6 yrs) and (2) shift (n = 87) or night (n = 6) workers (total n = 93; age: 37.7+/-9.7 yrs). Shift/night workers reported poor sleep more frequently than the daytime workers (20.4% vs. 1.2%, p < 0.01), as well as habitual difficulty in falling asleep (15.1% vs. 4.7%, p<0.01), long latency of sleep onset (28% vs. 7%, p<0.01), fragmented sleep (45.2% vs. 16.3%, p<0.01), short sleep episodes (44.1% vs. 16.3%, p < 0.01), irregular bedtimes (29.0% vs. 12.8%, p < 0.01), and feeling tired upon awakening (15.1% vs. 3.5%, p < 0.01). Habitual napping and loud snoring were reported twice as often in shift/night than in day workers (p < 0.01). Nightmares, somnambulism, and unpleasant feeling in the legs were equality reported by both groups (p > 0.05). Few offshore workers had sought medical help for their sleep problems. A higher number of shift/night workers reported feelings of sadness compared with day workers (26.9% vs. 9.3%, p < 0.01). The findings of this study show that subjective reports of sleep-related problems are quite common among Brazilian offshore shift workers. Reliance on self-reported sleep problems and a cross-sectional design are the main limitations of our study.     

Controlled Exposure to Light and Darkness Realigns the Salivary Cortisol Rhythm in Night Shift Workers

The efficacy of a light/darkness intervention designed to promote circadian adaptation to night shift work was tested in this combined field and laboratory study. Six full-time night shift workers (mean age ± SD:37.1 ± 8.1 yrs) were provided an intervention consisting of an intermittent exposure to full-spectrum bright white light (～2000 lux) in the first 6 h of their 8 h shift, shielding from morning light by tinted lenses (neutral gray density, 15% visual light transmission), and regular sleep/darkness episodes in darkened quarters beginning 2 h after the end of each shift. Five control group workers (41.1 ± 9.9 yrs) were observed in the presence of a regular sleep/darkness schedule only. Constant routines (CR) performed before and after a sequence of ～12 night shifts over 3 weeks revealed that treatment group workers displayed significant shifts in the time of peak cortisol expression and realignment of the rhythm with the night-oriented schedule. Smaller phase shifts, suggesting an incomplete adaptation to the shift work schedule, were observed in the control group. Our observations support the careful control of the pattern of light and darkness exposure for the adaptation of physiological rhythms to night shift work.     

Twelve-hour night shifts of healthcare workers: a risk to the patients?

We assessed the impact of 12h fixed night shift (19:00-07:00h) work, followed by 36h of off-time, on the sleep-wake cycle, sleep duration, self-perceived sleep quality, and work-time alertness on a group composed of 5 registered and 15 practical nurses. Wrist actigraphy (Ambulatory Monitoring, Inc.), with data analysis by the Cole-Kripke algorithm, was applied to determine sleep/wake episodes and their duration. The sleep episodes were divided into six categories: sleep during the night shift (x = 208.6; SD +/- 90.6 mins), sleep after the night shift (x = 138.7; SD +/- 79.6 min), sleep during the first night after the night work (x = 318.5; SD +/- 134.6 min), sleep before the night work (x = 104.3; SD +/- 44.1 min), diurnal sleep during the rest day (x = 70.5; SD +/- 43.0 min), and nocturnal sleep during the rest day (x = 310.4; SD +/- 188.9mins). A significant difference (p < .0001; T-test for dependent samples) was detected between the perceived quality of sleep of the three diurnal sleep categories compared to the three nocturnal sleep categories. Even thought the nurses slept (napped) during the night shift, their self-perceived alertness systematically decreased during it. Statistically significant differences were documented by one-way ANOVA (F = 40.534 p < .0001) among the alertness measurements done during the night shift. In particular, there was significant difference in the level of perceived alertness (p < .0001) between the 7th and 10th of the 12h night shift. These findings of decreased alertness during the terminal hours of the night shift are of concern, since they suggest risk of comprised patient care.     

The impact of sleep timing and bright light exposure on attentional impairment during night work

The prevalence of hazardous incidents induced by attentional impairment during night work and ensuing commute times is attributable to circadian misalignment and increased sleep pressure. In a 10-day shift work simulation protocol (4 day shifts and 3 night shifts), the efficacies of 2 countermeasures against nighttime (2300 to 0700 h) attentional impairment were compared: (1) Morning Sleep (0800 to 1600 h; n = 18) in conjunction with a phase-delaying light exposure (2300 to 0300 h), and (2) Evening Sleep (1400 to 2200 h; n = 17) in conjunction with a phase-advancing light exposure (0300 to 0700 h). Analysis of the dim light salivary melatonin onset indicated a modest but significant circadian realignment in both sleep groups (evening sleep: 2.27 +/- 0.6 h phase advance, p < 0.01; morning sleep: 4.98 +/- 0.43 h phase delay, p < 0.01). Daytime sleep efficiency and total sleep time did not differ between them or from their respective baseline sleep (2200 to 0600 h; p > 0.05). However, on the final night shift, the evening sleep subjects had 37% fewer episodes of attentional impairment (long response times: 22 +/- 4 vs. 35 +/- 4; p = 0.02) and quicker responses (p < 0.01) on the Psychomotor Vigilance Task than their morning sleep counterparts. Their response speed recovered to near daytime levels (p = 0.47), whereas those of the morning sleep subjects continued to be slower than their daytime levels (p = 0.008). It is concluded that partial circadian realignment to night work in combination with reduced homeostatic pressure contributed to the greater efficacy of a schedule of Evening Sleep with a phase-advancing light exposure as a countermeasure against attentional impairment, over a schedule of Morning Sleep with a phase-delaying light exposure. These results have important implications for managing patients with shift work disorder.     

Ring the bell for Matins: circadian adaptation to split sleep by cloistered monks and nuns

Cloistered monks and nuns adhere to a 10-century-old strict schedule with a common zeitgeber of a night split by a 2- to 3-h-long Office (Matins). The authors evaluated how the circadian core body temperature rhythm and sleep adapt in cloistered monks and nuns in two monasteries. Five monks and five nuns following the split-sleep night schedule for 5 to 46 yrs without interruption and 10 controls underwent interviews, sleep scales, and physical examination and produced a week-long sleep diary and actigraphy, plus 48-h recordings of core body temperature. The circadian rhythm of temperature was described by partial Fourier time-series analysis (with 12- and 24-h harmonics). The temperature peak and trough values and clock times did not differ between groups. However, the temperature rhythm was biphasic in monks and nuns, with an early decrease at 19:39 ± 4:30 h (median ± 95% interval), plateau or rise of temperature at 22:35 ± 00:23 h (while asleep) lasting 296 ± 39 min, followed by a second decrease after the Matins Office, and a classical morning rise. Although they required alarm clocks to wake-up for Matins at midnight, the body temperature rise anticipated the nocturnal awakening by 85 ± 15 min. Compared to the controls, the monks and nuns had an earlier sleep onset (20:05 ± 00:59 h vs. 00:00 ± 00:54 h, median ± 95% confidence interval, p= .0001) and offset (06:27 ± 0:22 h, vs. 07:37 ± 0:33 h, p= .0001), as well as a shorter sleep time (6.5 ± 0.6 vs. 7.6 ± 0.7 h, p= .05). They reported difficulties with sleep latency, sleep duration, and daytime function, and more frequent hypnagogic hallucinations. In contrast to their daytime silence, they experienced conversations (and occasionally prayers) in dreams. The biphasic temperature profile in monks and nuns suggests the human clock adapts to and even anticipates nocturnal awakenings. It resembles the biphasic sleep and rhythm of healthy volunteers transferred to a short (10-h) photoperiod and provides a living glance into the sleep pattern of medieval time.     

A Compromise Phase Position for Permanent Night Shift Workers: Circadian Phase after Two Night Shifts with Scheduled Sleep and Light/Dark Exposure

Night shift work is associated with a myriad of health and safety risks. Phase‐shifting the circadian clock such that it is more aligned with night work and day sleep is one way to attenuate these risks. However, workers will not be satisfied with complete adaptation to night work if it leaves them misaligned during days off. Therefore, the goal of this set of studies is to produce a compromise phase position in which individuals working night shifts delay their circadian clocks to a position that is more compatible with nighttime work and daytime sleep yet is not incompatible with late nighttime sleep on days off. This is the first in the set of studies describing the magnitude of circadian phase delays that occurs on progressively later days within a series of night shifts interspersed with days off. The series will be ended on various days in order to take a “snapshot” of circadian phase. In this set of studies, subjects sleep from 23:00 to 7:00 h for three weeks. Following this baseline period, there is a series of night shifts (23:00 to 07:00 h) and days off. Experimental subjects receive five 15 min intermittent bright light pulses (～3500 lux; ～1100 µW/cm²) once per hour during the night shifts, wear sunglasses that attenuate all visible wavelengths—especially short wavelengths (“blue‐blockers”)—while traveling home after the shifts, and sleep in the dark (08:30–15:30 h) after each night shift. Control subjects remain in typical dim room light (<50 lux) throughout the night shift, wear sunglasses that do not attenuate as much light, and sleep whenever they want after the night shifts. Circadian phase is determined from the circadian rhythm of melatonin collected during a dim light phase assessment at the beginning and end of each study. The sleepiest time of day, approximated by the body temperature minimum (T_min), is estimated by adding 7 h to the dim light melatonin onset. In this first study, circadian phase was measured after two night shifts and day sleep periods. The T_min of the experimental subjects (n=11) was 04:24±0.8 h (mean±SD) at baseline and 7:36±1.4 h after the night shifts. Thus, after two night shifts, the T_min had not yet delayed into the daytime sleep period, which began at 08:30 h. The T_min of the control subjects (n=12) was 04:00±1.2 h at baseline and drifted to 4:36±1.4 h after the night shifts. Thus, two night shifts with a practical pattern of intermittent bright light, the wearing of sunglasses on the way home from night shifts, and a regular sleep period early in the daytime, phase delayed the circadian clock toward the desired compromise phase position for permanent night shift workers. Additional night shifts with bright light pulses and daytime sleep in the dark are expected to displace the sleepiest time of day into the daytime sleep period, improving both nighttime alertness and daytime sleep but not precluding adequate sleep on days off.     

Controlled exposure to light and darkness realigns the salivary cortisol rhythm in night shift workers

The efficacy of a light/darkness intervention designed to promote circadian adaptation to night shift work was tested in this combined field and laboratory study. Six full-time night shift workers (mean age ± SD:37.1 ± 8.1 yrs) were provided an intervention consisting of an intermittent exposure to full-spectrum bright white light (∼2000 lux) in the first 6 h of their 8 h shift, shielding from morning light by tinted lenses (neutral gray density, 15% visual light transmission), and regular sleep/darkness episodes in darkened quarters beginning 2 h after the end of each shift. Five control group workers (41.1 ± 9.9 yrs) were observed in the presence of a regular sleep/darkness schedule only. Constant routines (CR) performed before and after a sequence of ∼12 night shifts over 3 weeks revealed that treatment group workers displayed significant shifts in the time of peak cortisol expression and realignment of the rhythm with the night-oriented schedule. Smaller phase shifts, suggesting an incomplete adaptation to the shift work schedule, were observed in the control group. Our observations support the careful control of the pattern of light and darkness exposure for the adaptation of physiological rhythms to night shift work.     

Light exposure among adolescents with delayed sleep phase disorder: a prospective cohort study

The objective of this study was to compare light exposure and sleep parameters between adolescents with delayed sleep phase disorder (DSPD; n=16, 15.3±1.8 yrs) and unaffected controls (n=22, 13.7±2.4 yrs) using a prospective cohort design. Participants wore wrist actigraphs with photosensors for 14 days. Mean hourly lux levels from 20:00 to 05:00 h and 05:00 to 14:00 h were examined, in addition to the 9-h intervals prior to sleep onset and after sleep offset. Sleep parameters were compared separately, and were also included as covariates within models that analyzed associations with specified light intervals. Additional covariates included group and school night status. Adolescent delayed sleep phase subjects received more evening (p< .02, 22:00-02:00 h) and less morning (p .05, 08:00-09:00 h and 10:00-12:00 h) light than controls, but had less pre-sleep exposure with adjustments for the time of sleep onset (p< .03, 5-7 h prior to onset hour). No differences were identified with respect to the sleep offset interval. Increased total sleep time and later sleep offset times were associated with decreased evening (p< .001 and p= .02, respectively) and morning (p= .01 and p< .001, respectively) light exposure, and later sleep onset times were associated with increased evening exposure (p< .001). Increased total sleep time also correlated with increased exposure during the 9 h before sleep onset (p= .01), and a later sleep onset time corresponded with decreased light exposure during the same interval (p< .001). Outcomes persisted regardless of school night status. In conclusion, light exposure interpretation requires adjustments for sleep timing among adolescents with DSPD. Pre- and post-sleep light exposures do not appear to contribute directly to phase delays. Sensitivity to morning light may be reduced among adolescents with DSPD.     

Variation in sleepiness during early morning shifts: a mixed model approach to an experimental field study of train drivers

The present study aimed to experimentally evaluate the effect of early morning shifts on sleep and sleepiness of train drivers during normal working conditions. A total of 17 experienced train drivers were studied during a 4.5 h drive in two directions with a 2.5 h break in between on three different shifts: an early shift that started at 05:49 h (train left at 06:18 h) and ended at 17:41h, a day shift (07:49-19:41 h), and an evening shift (09:49-21:41 h). Retrospective (since the last stop) ratings of mean sleepiness and peak sleepiness (Karolinska Sleepiness Scale--KSS: 1 = very alert, 9= very sleepy, fighting sleep, difficulty staying awake) were assessed at each stop during the drive. The results showed that sleep length was reduced (p <0.001) by 1 h and 2h, respectively, by the early shift compared to the day and evening shifts. The prevalence of severe sleepiness (KSS > or = 7) was high, especially during the early shift when 14 (82%) subjects reported at least one event during the drive. Application of the Generalized Linear Mixed Models (GLMM) to the sleepiness data showed that there was an increased risk for severe sleepiness during the early shift (OR = 4.9) that increased further with the length of the drive between stops (OR = 1.9, 15 min), suggesting an interaction between early morning shift and monotony. The findings have practical implications in risk assessment. Long drives without stops and other monotonous situations should have a higher risk rating for severe sleepiness in shifts with an early start before 06:00 h, compared to shifts that begin 2 h later.     

Building-site camps and extended work hours: A two-week monitoring of self-reported physical exertion, fatigue, and daytime sleepiness

Large-scale construction work often requires people to work longer daily hours and more than the ordinary five days in a row. In order to minimize transportation times and optimize the use of personnel, workers are sometimes asked to live in temporary building-site camps in the proximity of the work site. However, little is known about the biological and psychological effects of this experience. The objective of the present study was to investigate whether exposure to long work hours and extended workweeks while living in building-site camps in between work shifts was associated with a build-up of increased complaints of poor sleep, daytime sleepiness, physical exertion, and fatigue across a two-week work cycle. Two groups of construction workers were examined. The camp group of 13 participants (mean age: 42+/-11 S.D. yrs) lived in building-site camps and worked extended hours (between 07:00 and 18:00 h) and extended workweeks (six days in a row, one day off, five days in a row, nine days off). The home group of 16 participants (mean age 40+/-9 yrs) worked ordinary hours between 07:00 and 15:00 h and returned home after each workday. Self-ratings of daytime sleepiness (Karolinska Sleepiness Scale), physical exertion (Borg CR-10), and mood were obtained six or seven times daily during two workweeks. Fatigue ratings were obtained once daily in the evening, and ratings of sleep disturbances were obtained once daily in the morning with the Karolinska Sleep Diary. Data were evaluated in a repeated measures design. The results showed that both groups reported a similar level of daytime sleepiness, physical exertion, and mood across workdays and time points within a workday (all three-way interactions had p>0.898). Although the home group reported earlier wake-up times, the pattern of sleep disturbance ratings across the workdays did not differ between the groups. Both groups reported few sleep disturbances and good mood. However, the camp group reported higher physical exertion already at the start of work and showed a more gentle increase in ratings during the work shift and a smaller decline between the end of work and bedtime. The camp group also reported higher fatigue scores than the home group. However, none of the groups showed signs of increasing ratings in the progress of the two workweeks. For both groups, the ratings of daytime sleepiness formed a U-shaped pattern, with the highest scores at awakening and at bedtime. Yet, the camp group reported higher daytime sleepiness than the home group at lunch break and at the second break in the afternoon. In conclusion, there were no signs of fatigue build-up or accumulation of daytime sleepiness, physical exertion, or sleep disturbances in either group. Despite the fact that the camp group showed some signs of having trouble in recuperating in between work shifts, as indicated by the higher physical exertion ratings at the start of work, higher fatigue scores, and higher daytime sleepiness, the results constitute no real foundation for altering the camp group's current work schedule and living arrangements.     

Sleep and circadian phase in a ship's crew

Numerous factors influence the increased health risks of seamen. This study investigated sleep (by actigraphy) and the adaptation of the internal clock in watch-keeping crew compared to day workers, as possible contributory factors. Fourteen watch keepers, 4 h on, 8 h off (0800-1200/2000-2400 h, 1200-1600/2400-0400 h, 1600-2000/0400-0800 h) (fixed schedule, n = 6; rotating by delay weekly, n = 8), and 12 day workers participated during a voyage from the United Kingdom to Antarctica. They kept daily sleep diaries and wore wrist monitors for continuous recording of activity. Sleep parameters were derived from activity using the manufacturer's software and analyzed by repeated-measures ANOVA using SAS 8.2. Sequential urine samples were collected for 48 h weekly for 6-sulphatoxymelatonin measurement as an index of circadian rhythm timing. Individuals working watches of 1200-1600/2400-0400 h and 1600-2000/0400-0800 h had 2 sleeps daily, analyzed separately as main sleep (longest) and 2nd sleep. Main sleep duration was shorter in watch keepers than in day workers (p < 0.0001). Objective sleep quality was significantly compromised in rotaters compared to both day workers and fixed watch keepers, the most striking comparisons being sleep efficiency (percentage desired sleep time spent sleeping) main sleep (p < 0.0001) and sleep fragmentation (an index of restlessness) main sleep (p < 0.0001). The 2nd sleep was substantially less efficient than was the main sleep (p < 0.0001) for all watch keepers. There were few significant differences in sleep between the different watches in rotating watch keepers. Circadian timing remained constant in day workers. Timing of the 6-sulphatoxymelatonin rhythm was later for the watch of 1200-1600/2400-0400 h than for all others (1200-1600/2400-0400 h, 5.90 +/- 0.85 h; 1600-2000/0400-0800 h, 1.5 +/- 0.64 h; 0800-1200/ 2000-2400 h, 2.72 +/- 0.76 h; days, 2.09 +/- 0.68 h [decimal hours, mean +/- SEM]: ANOVA, p < 0.01). This study identifies weekly changes in watch time as a cause of poor sleep in watch keepers. The most likely mechanism is the inability of the internal clock to adapt rapidly to abrupt changes in schedule.     

Circadian rhythms of basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), cortisol, and melatonin in women with breast cancer

Background: Circadian rhythms in plasma concentrations of many hormones and cytokines determine their effects on target cells. Methods: Circadian variations were studied in cortisol, melatonin, cytokines (basic fibroblast growth factor [bFGF], EGF, insulin-like growth factor-1 [IGF-1]), and a cytokine receptor (insulin-like growth factor binding protein-3 [IGFBP-3]) in the plasma of 28 patients with metastatic breast cancer. All patients followed a diurnal activity pattern. Blood was drawn at 3h intervals during waking hours and once during the night, at 03:00. The plasma levels obtained by enzyme-linked immunoassay (ELISA) or radioimmunoassay (RIA) were evaluated by population mean cosinor (using local midnight as the phase reference and by one-way analysis of variance (ANOVA). Results: Cortisol and melatonin showed a high-amplitude circadian rhythm and a superimposed 12h frequency. bFGF showed a circadian rhythm with an acrophase around 13:00 with a peak-to-trough interval (double amplitude) of 18.2% and a superimposed 12h frequency. EGF showed a circadian rhythm with an acrophase around 14:20, a peak-to-trough interval of 25.8%, and a superimposed 12h frequency. IGF-1 showed a high value in the morning, which is statistically different t test) from the low value at 10:00, but a regular circadian or ultradian rhythm was not recognizable as a group phenomenon. IGFBP-3 showed a low-amplitude (peak-to-trough difference 8.4%) circadian rhythm with the acrophase around 11:00 and low values during the night. Conclusions: (1) Circadian periodicity is maintained in hospitalized patients with metastatic breast cancer. (2) Ultradian (12h) variations were superimposed on the circadian rhythms of the hormones and several of the cytokines measured. (3) Studies of hormones and cytokines in cancer patients have to take their biologic rhythms into consideration. (4) The circadian periodicity of tumor growth stimulating or restraining factors raises questions about circadian and/ or ultradian variations in the pathophysiology of breast cancer. (Chronobiology International, 18(4), 709-727)     

Sleepiness and sleep in a simulated "six hours on/six hours off" sea watch system

Ships are operated around the clock using rapidly rotating shift schedules called sea watch systems. Sea watch systems may cause fatigue, in the same way as other irregular working time arrangements. The present study investigated subjective sleepiness and sleep duration in connection with a 6 h on/6 h off duty system. The study was performed in a bridge simulator, very similar to those found on ships. Twelve officers divided into two groups participated in the study that lasted 66 h. Half of the subjects started with the 06:00-12:00 h watch and the other half with the 12:00-18:00 h watch. The subjects alternated between off-duty and on-duty for the remainder of the experimental period. Approximately halfway through the experiment, the 12:00-18:00 h watch was divided into two 3 h watches/off-duty periods. The effect of this was to reverse the on-duty/off-duty pattern between the two groups. This enabled all subjects to work the four possible watches (00:00-06:00 h, 06:00-12:00 h, 12:00-18:00 h, and 18:00-24:00 h) in an order that was essentially counterbalanced between groups. Ratings of sleepiness (Karolinska Sleepiness Scale; KSS) were obtained every 30 min during on-duty periods and if subjects were awake during off-duty periods. The subjectively rated duration of sleep was recorded after each off-duty period that preceded watch periods when KSS was rated. The results showed that the average level of sleepiness was significantly higher during the 00:00-06:00 h watch compared to the 12:00-18:00 h and 18:00-24:00 h watches, but not to the 06:00-12:00 h watch. Sleepiness also progressed significantly from the start toward the end of each watch, with the exception of the 06:00-12:00 h watch, when levels remained approximately stable. There were no differences between groups (i.e., the order between watches). Sleep duration during the 06:00-12:00 h off-duty period (3 h 29 min) was significantly longer than during the 12:00-18:00 h period (1 h 47 min) and the 18:00-24:00 h period (2 h 7 min). Sleep during the 00:00-06:00 h period (4 h 23 min) was longer than all sleep periods except the 06:00-12:00 h period. There were no differences between groups. In spite of sufficient opportunities for sleep, sleep was on the average around 1-1 h 30 min shorter than the 7-7 h 30 min that is considered “normal” during a 24 h period. This is probably a consequence of the difficulty to sleep during daytime due to the alerting effects of the circadian rhythm. Also, sleepiness during the night and early mornings reached high levels, which may be explained by a combination of working close to or during the circadian trough of alertness and the relatively short sleep periods obtained. An initial suppression of sleepiness was observed during all watches, except for the 06:00-12:00 h watch. This suppression may be explained by the “masking effect” exerted by the relative high levels of activity required when taking over the responsibility of the ship. Toward the end of watches, the levels of sleepiness progressively increased to relatively high levels, at least during the 00:00-06:00 h watch. Presumably, initially high levels of activity are replaced by routine and even boredom.     

Timing Light Treatment for Eastward and Westward Travel Preparation

Jet lag degrades performance and operational readiness of recently deployed military personnel and other travelers. The objective of the studies reported here was to determine, using a narrow bandwidth light tower (500 nm), the optimum timing of light treatment to hasten adaptive circadian phase advance and delay. Three counterbalanced treatment order, repeated measures studies were conducted to compare melatonin suppression and phase shift across multiple light treatment timings. In Experiment 1, 14 normal healthy volunteers (8 men/6 women) aged 34.9±8.2 yrs (mean±SD) underwent light treatment at the following times: A) 06:00 to 07:00 h, B) 05:30 to 07:30 h, and C) 09:00 to 10:00 h (active control). In Experiment 2, 13 normal healthy subjects (7 men/6 women) aged 35.6±6.9 yrs, underwent light treatment at each of the following times: A) 06:00 to 07:00 h, B) 07:00 to 08:00 h, C) 08:00 to 09:00 h, and a no-light control session (D) from 07:00 to 08:00 h. In Experiment 3, 10 normal healthy subjects (6 men/4 women) aged 37.0±7.7 yrs underwent light treatment at the following times: A) 02:00 to 03:00 h, B) 02:30 to 03:30 h, and C) 03:00 to 04:00 h, with a no-light control (D) from 02:30 to 03:30 h. Dim light melatonin onset (DLMO) was established by two methods: when salivary melatonin levels exceeded a 1.0 pg/ml threshold, and when salivary melatonin levels exceeded three times the 0.9 pg/ml sensitivity of the radioimmunoasssy. Using the 1.0 pg/ml DLMO, significant phase advances were found in Experiment 1 for conditions A (p?<?.028) and B (p?<?0.004). Experiment 2 showed significant phase advances in conditions A (p?<?0.018) and B (p?<?0.003) but not C (p?<?0.23), relative to condition D. In Experiment 3, only condition B (p?<?0.035) provided a significant phase delay relative to condition D. Similar but generally smaller phase shifts were found with the 2.7 pg/ml DLMO method. This threshold was used to analyze phase shifts against circadian time of the start of light treatment for all three experiments. The best fit curve applied to these data (R²?=?0.94) provided a partial phase-response curve with maximum advance at approximately 9–11 h and maximum delay at approximately 5–6 h following DLMO. These data suggest largest phase advances will result when light treatment is started between 06:00 and 08:00 h, and greatest phase delays will result from light treatment started between 02:00 to 03:00 h in entrained subjects with a regular sleep wake cycle (23:00 to 07:00 h).     

Circadian adaptation to night-shift work by judicious light and darkness exposure

In this combined field and laboratory investigation, the authors tested the efficacy of an intervention designed to promote circadian adaptation to night-shift work. Fifteen nurses working permanent night schedules (> or = 8 shifts/ 15 days) were recruited from area hospitals. Following avacation period of > or = 10 days on a regular daytime schedule, workers were admitted to the laboratory for the assessment of circadian phase via a 36-h constant routine. They returned to work approximately 12 night shifts on their regular schedules under one of two conditions. Treatment group workers (n = 10, mean age +/- SD = 41.7 +/- 8.8 years) received an intervention including 6 h of intermittent bright-light exposure in the workplace (approximately 3,243 lux) and shielding from bright morning outdoor light with tinted goggles (15% visual light transmission). Control group workers (n = 9, mean age +/- SD = 42.0 +/- 7.2 years) were observed in their habitual work environments. On work days, participants maintained regular sleep/wake schedules including a single 8-h sleep/darkness episode beginning 2 h after the end of the night shift. A second 36-h constant routine was performed following the series of night shifts. In the presence of the intervention, circadian rhythms of core body temperature and salivary melatonin cycles were delayed by an average (+/- SEM) of -9.32 +/- 1.06 h and -11.31 +/- 1.13 h, respectively. These were significantly greater than the phase delays of -4.09 +/- 1.94 h and -5.08 +/- 2.32 h displayed by the control group (p = 0.03 and p = 0.02, respectively). The phase angle between circadian markers and the shifted schedule was reestablished to its baseline position only in the treatment group of workers. These results support the efficacy of a practical intervention for promoting circadian adaptation to night-shift work under field conditions. They also underline the importance of controlling the overall pattern of exposure to light and darkness in circadian adaptation to shifted sleep/wake schedules.     

Phase-dependent effect of room light exposure in a 5-h advance of the sleep-wake cycle: implications for jet lag

The acute disruption in sleep quality, vigilance levels, and cognitive and athletic performance observed after transmeridian flights is presumed to be the result of a transient misalignment between the endogenous circadian pacemaker and the shifted sleep schedule. Several laboratory and field experiments have demonstrated that exposure to bright artificial light can accelerate circadian entrainment to a shifted sleep-wake schedule. In the present study, the authors investigated whether the schedule of exposure to indoor room light, to which urban dwellers are typically exposed, can substantially affect circadian adaptation to a simulated eastward voyage. We enrolled 15 healthy young men in a laboratory simulation of a Montreal-to-London voyage. Subjects were exposed to 6 h of room light (mean +/- SD: 379+/-10) prior to bedtime (n = 7) or when on a progressively advancing schedule (n = 8) early in the day. The remaining 10 hours of wakefulness were spent in dim light (4+/-1 lux). Circadian assessments, performed via the constant routine procedure, evaluated the phase of the endogenous circadian rhythms of core body temperature and plasma melatonin before and after 1 week on the shifted schedule. At the end of the study, only subjects exposed to room light on the advancing schedule expressed oscillations of the endogenous circadian pacemaker in phase with the new sleep-wake cycle. In this group, a mean advance shift of the nadir of core body temperature of +5:22+/-0:15 h was observed, with parallel shifts in plasma melatonin concentration and subjective alertness. The circadian rhythms of subjects exposed to room light later in the day remained much more adjusted to the departure than to the destination time zone. These results demonstrate that the schedule of exposure to room light can substantially affect circadian adaptation to a shifted sleep-wake schedule.