Sleep and cortical temperature in the Djungarian hamster under baseline conditions and after sleep deprivation

The Djungarian hamster (Phodopus sungorus) is a markedly photoperiodic rodent which exhibits daily torpor under short photoperiod. Normative data were obtained on vigilance states, electroencephalogram (EEG) power spectra (0.25–25.0 Hz), and cortical temperature (T_CRT) under a 168 h light-dark schedule, in 7 Djungarian hamsters for 2 baseline days, 4 h sleep deprivation (SD) and 20 h recovery.During the baseline days total sleep time amounted to 59% of recording time, 67% in the light period and 43% in the dark period. The 4 h SD induced a small increase in the amount of non-rapid eye movement (NREM) sleep and a marked increase in EEG slow-wave activity (SWA; mean power density 0.75–4.0 Hz) within NREM sleep in the first hours of recovery. T_CRT was lower in the light period than in the dark period. It decreased at transitions from either waking or rapid eye movement (REM) sleep to NREM sleep, and increased at the transition from NREM sleep to waking or REM sleep. After SD, T_CRT was lower in all vigilance states.In conclusion, the sleep-wake pattern, EEG spectrum, and time course of T_CRT in the Djungarian hamster are similar to other nocturnal rodents. Also in the Djungarian hamster the time course of SWA seems to reflect a homeostatically regulated process as was formulated in the two-process model of sleep regulation.Abbreviations EEG electroencephalogram - EMG electromyogram - N NREM sleep - NREM non-rapid eye movement - R REM sleep - REM rapid eye movement - SD sleep deprivation - SWA slow-wave activity - T_CRT cortical temperature - TST total sleep time - VS vigilance state - W waking     

Shortening of the photoperiod affects sleep distribution, EEG and cortical temperature in the Djungarian hamster

To asses the influence of photoperiod on sleep regulation EEG, EMG, and cortical temperature were continuously recorded for two baseline days and after 4 h sleep deprivation in Djungarian hamsters (Phodopus sungorus) adapted to a short photoperiod (light dark 816). Comparison to previous data collected in a long photoperiod (lightdark 168) showed several major effects of photoperiod: 1. A prominent change in the 24-h distribution, duration and number of vigilance state episodes, whereas the total amount of sleep and waking was unchanged; 2. Cortical temperature was 0.7°C lower in the short photoperiod; 3. There was a significant negative correlation between cortical temperature and the frequency of REM sleep episodes; and 4. Absolute EEG power density showed a marked reduction in the short photoperiod. After sleep deprivation EEG slow-wave activity (mean power density 0.75–4.0 Hz) in NREM sleep showed a remarkably similar increase in both photoperiods demonstrating the robustness of the homeostatic regulation of sleep. Cortical temperature remained above baseline values after sleep deprivation in the short photoperiod whereas a negative rebound was present in the long photoperiod. Our results support the hypothesis that cortical temperature has a strong influence on REM sleep propensity and indicate the possibility of an optimum cortical temperature for recovery sleep after sleep deprivation. The lower EEG power density in the short photoperiod may contribute to energy conservation.Abbreviations LP long photoperiod - NREM non-rapid-eye-movement - REM rapid-eye-movement - SCN suprachiasmatic nucleus - SD sleep deprivation - SP short photoperiod - SWA slow-wave activity - T _CRT cortical temperature     

AMBER LENSES TO BLOCK BLUE LIGHT AND IMPROVE SLEEP: A RANDOMIZED TRIAL

All light is not equal: blue wavelengths are the most potent portion of the visible electromagnetic spectrum for circadian regulation. Therefore, blocking blue light could create a form of physiologic darkness. Because the timing and quantity of light and darkness both affect sleep, evening use of amber lenses to block blue light might affect sleep quality. Mood is also affected by light and sleep; therefore, mood might be affected by blue light blockade. In this study, 20 adult volunteers were randomized to wear either blue-blocking (amber) or yellow-tinted (blocking ultraviolet only) safety glasses for 3?h prior to sleep. Participants completed sleep diaries during a one-week baseline assessment and two weeks' use of glasses. Outcome measures were subjective: change in overall sleep quality and positive/negative affect. Results demonstrated that sleep quality at study outset was poorer in the amber lens than the control group. Two- by three-way ANOVA revealed significant (p?<?.001) interaction between quality of sleep over the three weeks and experimental condition. At the end of the study, the amber lens group experienced significant (p?<?.001) improvement in sleep quality relative to the control group and positive affect (p?=?.005). Mood also improved significantly relative to controls. A replication with more detailed data on the subjects' circadian baseline and objective outcome measures is warranted. (Author correspondence: jphelps@samhealth.org)     

EVENING DAYLIGHT MAY CAUSE ADOLESCENTS TO SLEEP LESS IN SPRING THAN IN WINTER

Sleep restriction commonly experienced by adolescents can stem from a slower increase in sleep pressure by the homeostatic processes and from phase delays of the circadian system. With regard to the latter potential cause, the authors hypothesized that because there is more natural evening light during the spring than winter, a sample of adolescent students would be more phase delayed in spring than in winter, would have later sleep onset times, and because of fixed school schedules would have shorter sleep durations. Sixteen eighth-grade subjects were recruited for the study. The authors collected sleep logs and saliva samples to determine their dim light melatonin onset (DLMO), a well-established circadian marker. Actual circadian light exposures experienced by a subset of 12 subjects over the course of 7 days in winter and in spring using a personal, head-worn, circadian light measurement device are also reported here. Results showed that this sample of adolescents was exposed to significantly more circadian light in spring than in winter, especially during the evening hours when light exposure would likely delay circadian phase. Consistent with the light data, DLMO and sleep onset times were significantly more delayed, and sleep durations were significantly shorter in spring than in winter. The present ecological study of light, circadian phase, and self-reported sleep suggests that greater access to evening daylight in the spring may lead to sleep restriction in adolescents while attending school. Therefore, lighting schemes that reduce evening light in the spring may encourage longer sleep times in adolescents. (Author correspondence: figuem@rpi.edu)     

Effects of electroacupuncture at ‘Anmian (Extra)’ acupoints on sleep activities in rats: The implication of the caudal nucleus tractus solitarius

Electroacupuncture (EAc) possesses a broad therapeutic effect, including improvement of sleep disturbances. The mechanism of sleep improvement with EAc, however, is still unclear. The present study investigated the effects of EAc stimulation of Anmian (extra) acupoints on sleep organization and the implication of an active structure, the caudal nucleus tractus solitarius (NTS). Rats were implanted with electroencephalogram (EEG) recording electrodes, and 32-gauge acupuncture needles were bilaterally inserted into Anmian (extra) acupoints in the rats, followed by electrical stimulation for 20 min. Twenty-three-hour continuous EEGs were then recorded. Results showed that rapid eye movement sleep (REMS) was enhanced during the dark period when a single EAc stimulation was given 25 min prior to the onset of the dark period. REMS and slow-wave sleep (SWS) increased during the dark period after administration of EAc stimuli on 2 consecutive days. Electrical stimulation of non-acupoints produced no change in the sleep pattern. Pharmacological blockade of muscarinic cholinergic receptors by systemic administration of scopolamine dose-dependently attenuated EAc-induced changes in REMS and SWS. Furthermore, electrical lesions in the bilateral caudal NTS produced significant blockade of EAc-induced sleep enhancement. However, in rats without EAc, scopolamine increased SWS during the dark period, but caudal NTS lesions did not alter sleep. In addition, neither EAc nor scopolamine with EAc manipulation produced any change in the slow-wave activity (SWA) during SWS; however, the SWA during SWS was significantly reduced after caudal NTS lesion with EAc. These results suggest that the caudal NTS may be involved in the regulation of EAc-induced sleep alterations.     

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. (Author correspondence: auger.raymond1@mayo.edu)     

Photic Resetting in Night-Shift Work: Impact on Nurses' Sleep

The objective of this study was to quantify daytime sleep in night-shift workers with and without an intervention designed to recover the normal relationship between the endogenous circadian pacemaker and the sleep/wake cycle. Workers of the treatment group received intermittent exposure to full-spectrum bright light during night shifts and wore dark goggles during the morning commute home. All workers maintained stable 8-h daytime sleep/darkness schedules. The authors found that workers of the treatment group had daytime sleep episodes that lasted 7.1?±?.1?h (mean?±?SEM) versus 6.6?±?.2?h for workers in the control group (p?=?.04). The increase in total sleep time co-occurred with a larger proportion of the melatonin secretory episode during daytime sleep in workers of the treatment group. The results of this study showed reestablishment of a phase angle that is comparable to that observed on a day-oriented schedule favors longer daytime sleep episodes in night-shift workers. (Author correspondence: diane.boivin@douglas.mcgill.ca)     

Relationship of Chronotype to Sleep,Light Exposure,and Work-Related Fatigue in Student Workers

Students who work during the school year face the potential of sleep deprivation and its effects, since they have to juggle between school and work responsibilities along with social life. This may leave them with less time left for sleep than their nonworking counterparts. Chronotype is a factor that may exert an influence on the sleep of student workers. Also, light and social zeitgebers may have an impact on the sleep-related problems of this population. This study aimed to document sleep, light exposure patterns, social rhythms, and work-related fatigue of student workers aged 19–21 yrs and explore possible associations with chronotype. A total of 88 student workers (mean?±?SD: 20.18?±?.44 yrs of age; 36 males/52 females) wore an actigraph (Actiwatch-L; Mini-Mitter/Respironics,Bend, OR) and filled out the Social Rhythm Metric for two consecutive weeks during the school year. Also, they completed the Morningness-Eveningness Questionnaire (MEQ), Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), and Occupational Fatigue Exhaustion/Recovery Scale (OFER). Repeated and one-way analyses of variance (ANOVAs), Pearson's chi-square tests, and correlation coefficients were used for statistical comparisons. Subjects slept an average of 06:28?h/night. Actigraphic sleep parameters, such as sleep duration, sleep efficiency, wake after sleep onset, and sleep latency, did not differ between chronotypes. Results also show that evening types (n?=?17) presented lower subjective sleep quality than intermediate types (n?=?58) and morning types (n?=?13). Moreover, evening types reported higher levels of chronic work-related fatigue, exhibited less regular social rhythms, and were exposed to lower levels of light during their waking hours (between 2 and 11 h after wake time) as compared to intermediate types and morning types. In addition, exposure to light intensities between 100 and 500 lux was lower in evening types than in intermediate types and morning types. However, bright light exposure (≥1000 lux) did not differ between chronotypes. In conclusion, results suggest that student workers may constitute a high-risk population for sleep deprivation. Evening types seemed to cope less well with sleep deprivation, reporting poorer sleep quality and higher levels of work-related fatigue than intermediate types and morning types. The higher chronic work-related fatigue of evening types may be linked to their attenuated level of light exposure and weaker social zeitgebers. These results add credence to the hypothesis that eveningness entails a higher risk of health-impairing behaviors. (Author correspondence: luc.laberge@uqac.ca)     

Assessment of a New Dynamic Light Regimen in a Nuclear Power Control Room Without Windows on Quickly Rotating Shiftworkers—Effects on Health,Wakefulness, and Circadian Alignment: A Pilot Study

The aim of the study was to test whether a new dynamic light regime would improve alertness, sleep, and adaptation to rotating shiftwork. The illumination level in a control room without windows at a nuclear power station was ～200 lux (straight-forward horizontal gaze) using a weak yellow light of 200 lux, 3000 K (Philips Master TLD 36 W 830). New lighting equipment was installed in one area of the control room above the positions of the reactor operators. The new lights were shielded from the control group by a distance of >6?m, and the other operators worked at desks turned away from the new light. The new lights were designed to give three different light exposures: (i) white/blue strong light of 745 lux, 6000 K; (ii) weak yellow light of 650 lux, 4000 K; and (iii) yellow moderate light of 700 lux, 4000 K. In a crossover design, the normal and new light exposures were given during a sequence of three night shifts, two free days, two morning shifts, and one afternoon shift (NNN?+?MMA), with 7 wks between sessions. The operators consisted of two groups; seven reactor operators from seven work teams were at one time exposed to the new equipment and 16 other operators were used as controls. The study was conducted during winter with reduced opportunities of daylight exposure during work, after night work, or before morning work. Operators wore actigraphs, filled in a sleep/wake diary, including ratings of sleepiness on the Karolinska Sleepiness Scale (KSS) every 2?h, and provided saliva samples for analysis of melatonin at work (every 2nd h during one night shift and first 3?h during one morning shift). Results from the wake/sleep diary showed the new light treatment increased alertness during the 2nd night shift (interaction group?×?light?×?time, p < .01). Time of waking was delayed in the light condition after the 3rd night shift (group?×?light, p < .05), but the amount of wake time during the sleep span increased after the 2nd night shift (p < .05), also showing a tendency to affect sleep efficiency (p < .10). Effects on circadian phase were difficult to establish given the small sample size and infrequent sampling of saliva melatonin. Nonetheless, it seems that appropriate dynamic light in rooms without windows during the dark Nordic season may promote alertness, sleep, and better adaptation to quickly rotating shiftwork. (Author correspondence: arne.lowden@stress.su.se)     

Effects of tryptophan-rich breakfast and light exposure during the daytime on melatonin secretion at night

Background

The purpose of the present study is to investigate effects of tryptophan intake and light exposure on melatonin secretion and sleep by modifying tryptophan ingestion at breakfast and light exposure during the daytime, and measuring sleep quality (by using actigraphy and the OSA sleep inventory) and melatonin secretion at night.

Methods

Thirty three male University students (mean ± SD age: 22 ± 3.1 years) completed the experiments lasting 5 days and 4 nights. The subjects were randomly divided into four groups: Poor*Dim (n = 10), meaning a tryptophan-poor breakfast (55 mg/meal) in the morning and dim light environment (<50 lx) during the daytime; Rich*Dim (n = 7), tryptophan-rich breakfast (476 mg/meal) and dim light environment; Poor*Bright (n = 9), tryptophan-poor breakfast and bright light environment (>5,000 lx); and Rich*Bright (n = 7), tryptophan-rich breakfast and bright light.

Results

Saliva melatonin concentrations on the fourth day were significantly lower than on the first day in the Poor*Dim group, whereas they were higher on the fourth day in the Rich*Bright group. Creatinine-adjusted melatonin in urine showed the same direction as saliva melatonin concentrations. These results indicate that the combination of a tryptophan-rich breakfast and bright light exposure during the daytime could promote melatonin secretion at night; further, the observations that the Rich*Bright group had higher melatonin concentrations than the Rich*Dim group, despite no significant differences being observed between the Poor*Dim and Rich*Dim groups nor the Poor*Bright and Rich*Bright groups, suggest that bright light exposure in the daytime is an important contributor to raised melatonin levels in the evening.

Conclusions

This study is the first to report the quantitative effects of changed tryptophan intake at breakfast combined with daytime light exposure on melatonin secretion and sleep quality. Evening saliva melatonin secretion changed significantly and indicated that a tryptophan-rich breakfast and bright light exposure during the daytime promoted melatonin secretion at this time.     

Association between delayed bedtime and sleep-related problems among community-dwelling 2-year-old children in Japan

Background

Although delayed sleep timing causes many socio-psycho-biological problems such as sleep loss, excessive daytime sleepiness, obesity, and impaired daytime neurocognitive performance in adults, there are insufficient data showing the clinical significance of a ‘night owl lifestyle’ in early life. This study examined the association between habitual delayed bedtime and sleep-related problems among community-dwelling 2-year-old children in Japan.

Methods

Parents/caregivers of 708 community-dwelling 2-year-old children in Nishitokyo City, Tokyo, participated in the study. The participants answered a questionnaire to evaluate their child’s sleep habits and sleep-related problems for the past 1 month.

Results

Of the 425 children for whom complete data were collected, 90 (21.2%) went to bed at 22:00 or later. Children with delayed bedtime showed significantly more irregular bedtime, delayed wake time, shorter total sleep time, and difficulty in initiating and terminating sleep. Although this relationship indicated the presence of sleep debt in children with delayed bedtime, sleep onset latency did not differ between children with earlier bedtime and those with delayed bedtime. Rather, delayed bedtime was significantly associated with bedtime resistance and problems in the morning even when adjusting for nighttime and daytime sleep time.

Conclusions

Even in 2-year-old children, delayed bedtime was associated with various sleep-related problems. The causal factors may include diminished homeostatic sleep drive due to prolonged daytime nap as well as diurnal preference (morning or night type) regulated by the biological clock.     

Subjective Sleep Quality Exclusively Mediates the Relationship Between Morningness-Eveningness Preference and Self-Perceived Stress Response

Eveningness preference has been associated with lower sleep quality and higher stress response compared with morningness preference. In the current study, female morning (n?=?27) and evening (n?=?28) types completed the Pittsburgh Sleep Quality Index (PSQI) and were additionally challenged with an arithmetic stress-induction task. Evening types reported lower subjective sleep quality and longer sleep latency than morning types. Furthermore, evening types reported higher self-perceived stress after the task than morning types. Subjective sleep quality fully mediated the relationship between morningness-eveningness preference and stress response. Poor sleep quality may, therefore, contribute to the elevated health risk in evening types. (Author correspondence: karolin.roeser@uni-wuerzburg.de)     

Time-of-Day Mediates the Influences of Extended Wake and Sleep Restriction on Simulated Driving

Although a nonlinear time-of-day and prior wake interaction on performance has been well documented, two recent studies have aimed to incorporate the influences of sleep restriction into this paradigm. Through the use of sleep-restricted forced desynchrony protocols, both studies reported a time-of-day?×?sleep restriction interaction, as well as a time-of-day?×?prior wake?×?sleep dose three-way interaction. The current study aimed to investigate these interactions on simulated driving performance, a more complex task with ecological validity for the problem of fatigued driving. The driving performance of 41 male participants (mean?±?SD: 22.8 ±2.2 yrs) was assessed on a 10-min simulated driving task with the standard deviation of lateral position (SDLAT) measured. Using a between-group design, participants were subjected to either a control condition of 9.33?h of sleep/18.66?h of wake, a moderate sleep-restriction (SR) condition of 7?h of sleep/21?h of wake, or a severe SR condition of 4.66?h of sleep/23.33?h of wake. In each condition, participants were tested at 2.5-h intervals after waking across 7?×?28-h d of forced desynchrony. Driving sessions occurred at nine doses of prior wake, within six divisions of the circadian cycle based on core body temperature (CBT). Mixed-models analyses of variance (ANOVAs) revealed significant main effects of time-of-day, prior wake, sleep debt, and sleep dose on SDLAT. Additionally, significant two-way interactions of time-of-day?×?prior wake and time-of-day?×?sleep debt, as well as significant three-way interactions of time-of-day?×?prior wake?×?sleep debt and time-of-day?×?sleep debt?×?sleep dose were observed. Although limitations such as the presence of practice effects and large standard errors are noted, the study concludes with three findings. The main effects demonstrate that extending wake, reducing sleep, and driving at poor times of day all significantly impair driving performance at an individual level. In addition to this, combining either extended wake or a sleep debt with the early morning hours greatly decreases driving performance. Finally, operating under the influence of a reduced sleep dose can greatly decrease performance at all times of the day. (Author correspondence: raymond.matthews@unisa.edu.au)     

Elevated Variance in Heart Rate During Slow-Wave Sleep After Late-Night Physical Activity

This study investigates the effect of mild physical activity before bedtime on the sleep pattern and heart rate during the night. Nine healthy subjects underwent a habituation night, a reference night, and a physical induction night. The physical induction night did not alter the sleep pattern. Physical activity before bedtime resulted in higher heart rate variance during slow-wave sleep. The low-frequency/high-frequency component (LF/HF) ratio during slow-wave sleep in the physical induction night was significantly higher than during the reference night. Increased mean heart rate and higher LF/HF ratio are related to decreased parasympathetic dominance. Exercise up to 1?h before bedtime thus seems to modify the quality of sleep. (Author correspondence: Daniel.Berckmans@biw.kuleuven.be)     

Impact of Perinatal Photoperiod on the Chronotype of 11- to 18-Year-Olds in Northern European Russia

The study investigates the effect of the month of birth and ambient light conditions at birth on sleep length and chronotype among residents of high latitudes. The authors surveyed 1172 persons (609 girls, 563 boys) age 11 to 18 yrs living in five villages and four towns located between 59.5°N and 67.6°N latitude. Survey participation was voluntary and anonymous. Sleep length and chronotype were assessed using the Munich chronotype questionnaire (MCTQ). The study showed the sleep length and chronotype of the children and adolescents depended on sex, age, type of settlement (town/village), and latitude of residence. Latitude exerted a stronger impact on sleep length and chronotype of children and adolescents living in villages than on those of their urban counterparts. Month of birth had no effect on sleep length and chronotype. There was a significant effect of the time of sunrise, sunset, and day length at birth on the chronotype of children and adolescents. A later chronotype was observed in the sample of young persons living above the Arctic Circle who were born during the polar day and polar night. (Author correspondence: borisenkov@physiol.komisc.ru)     

Circadian Preference and Sleep-Wake Regularity: Associations With Self-Report Sleep Parameters in Daytime-Working Adults

The aim of this study was to explore how interindividual differences in circadian type (morningness) and sleep timing regularity might be related to subjective sleep quality and quantity. Self-report circadian phase preference, sleep timing, sleep quality, and sleep duration were assessed in a sample of 62 day-working adults (33.9% male, age 23–48 yrs). The Pittsburgh Sleep Quality Index (PSQI) measured subjective sleep quality and the Sleep Timing Questionnaire (STQ) assessed habitual sleep latency and minutes awake after sleep onset. The duration, timing, and stability of sleep were assessed using the STQ separately for work-week nights (Sunday–Thursday) and for weekend nights (Friday and Saturday). Morningness-eveningness was assessed using the Composite Scale of Morningness (CSM). Daytime sleepiness was measured using the Epworth Sleepiness Scale (ESS). A morning-type orientation was associated with longer weekly sleep duration, better subjective sleep quality, and shorter sleep-onset latency. Stable weekday rise-time correlated with better self-reported sleep quality and shorter sleep-onset latency. A more regular weekend bedtime was associated with a shorter sleep latency. A more stable weekend rise-time was related to longer weekday sleep duration and lower daytime sleepiness. Increased overall regularity in rise-time was associated with better subjective sleep quality, shorter sleep-onset latency, and higher weekday sleep efficiency. Finally, a morning orientation was related to increased regularity in both bedtimes and rise-times. In conclusion, in daytime workers, a morning-type orientation and more stable sleep timing are associated with better subjective sleep quality. (Author correspondence: asoehner@berkeley.edu)     

WORK HOURS AND SLEEP/WAKE BEHAVIOR OF AUSTRALIAN HOSPITAL DOCTORS

The objective of the study was to describe the work and sleep patterns of doctors working in Australian hospitals. Specifically, the aim was to examine the influence of work-related factors, such as hospital type, seniority, and specialty on work hours and their impact on sleep. A total of 635 work periods from 78 doctors were analyzed together with associated sleep history. Work and sleep diary information was validated against an objective measure of sleep/wake activity to provide the first comprehensive database linking work and sleep for individual hospital doctors in Australia. Doctors in large and small facilities had fewer days without work than those doctors working in medium-sized facilities. There were no significant differences in the total hours worked across these three categories of seniority; however, mid-career and senior doctors worked more overnight and weekend on-call periods than junior doctors. With respect to sleep, although higher work hours were related to less sleep, short sleeps (< 5 h in the 24 h prior to starting work) were observed at all levels of prior work history (including no work). In this population of Australian hospital doctors, total hours worked do impact sleep, but the pattern of work, together with other nonwork factors are also important mediators. (Author correspondence: sally.ferguson@unisa.edu.au)     

A Personal Light-Treatment Device for Improving Sleep Quality in the Elderly: Dynamics of Nocturnal Melatonin Suppression at Two Exposure Levels

Light treatment has been used as a non-pharmacological tool to help mitigate poor sleep quality frequently found in older people. In order to increase compliance to non-pharmacological light treatments, new, more efficacious light-delivery systems need to be developed. A prototype personal light-treatment device equipped with low brightness blue light-emitting diodes (LEDs) (peak wavelength near 470 nm) was tested for its effectiveness in suppressing nocturnal melatonin, a measure of circadian stimulation. Two levels of corneal irradiance were set to deliver two prescribed doses of circadian light exposure. Eleven older subjects, between 51 and 80 yrs of age who met the selection criteria, were exposed to a high and a low level of light for 90 min on separate nights from the personal light-treatment device. Blood and saliva samples were collected at prescribed times for subsequent melatonin assay. After 1 h of light exposure, the light-induced nocturnal melatonin suppression level was about 35% for the low-light level and about 60% for the high-light level. The higher level of blue light suppressed melatonin more quickly, to a greater extent over the course of the 90 min exposure period, and maintained suppression after 60 min. The constant exposure of the low-light level resulted in a decrease in nocturnal melatonin suppression for the last sampling time, whereas for the high-light level, suppression continued throughout the entire exposure period. The present study performed with healthy adults suggests that the tested personal light-treatment device might be a practical, comfortable, and effective way to deliver light treatment to those suffering from circadian sleep disorders; however, the acceptance and effectiveness of personal light-treatment devices by older people and by other segments of the population suffering from sleep disorders in a real-life situation need to be directly tested. (Author correspondence: figuem@rpi.edu)     

Authors' response

At Arctic and Antarctic latitudes, personnel are deprived of natural sunlight in winter and have continuous daylight in summer: light of sufficient intensity and suitable spectral composition is the main factor that maintains the 24-h period of human circadian rhythms. Thus, the status of the circadian system is of interest. Moreover, the relatively controlled artificial light conditions in winter are conducive to experimentation with different types of light treatment. The hormone melatonin and/or its metabolite 6-sulfatoxymelatonin (aMT6s) provide probably the best index of circadian (and seasonal) timing. A frequent observation has been a delay of the circadian system in winter. A skeleton photoperiod (2?×?1-h, bright white light, morning and evening) can restore summer timing. A single 1-h pulse of light in the morning may be sufficient. A few people desynchronize from the 24-h day (free-run) and show their intrinsic circadian period, usually >24?h. With regard to general health in polar regions, intermittent reports describe abnormalities in various physiological processes from the point of view of daily and seasonal rhythms, but positive health outcomes are also published. True winter depression (SAD) appears to be rare, although subsyndromal SAD is reported. Probably of most concern are the numerous reports of sleep problems. These have prompted investigations of the underlying mechanisms and treatment interventions. A delay of the circadian system with “normal” working hours implies sleep is attempted at a suboptimal phase. Decrements in sleep efficiency, latency, duration, and quality are also seen in winter. Increasing the intensity of ambient light exposure throughout the day advanced circadian phase and was associated with benefits for sleep: blue-enriched light was slightly more effective than standard white light. Effects on performance remain to be fully investigated. At 75°S, base personnel adapt the circadian system to night work within a week, in contrast to temperate zones where complete adaptation rarely occurs. A similar situation occurs on high-latitude North Sea oil installations, especially when working 18:00–06:00?h. Lack of conflicting light exposure (and “social obligations”) is the probable explanation. Many have problems returning to day work, showing circadian desynchrony. Timed light treatment again has helped to restore normal phase/sleep in a small number of people. Postprandial response to meals is compromised during periods of desynchrony with evidence of insulin resistance and elevated triglycerides, risk factors for heart disease. Only small numbers of subjects have been studied intensively in polar regions; however, these observations suggest that suboptimal light conditions are deleterious to health. They apply equally to people living in temperate zones with insufficient light exposure. (Author correspondence: arendtjo@gmail.com)     

EFFECTS OF ARTIFICIAL DAWN ON SUBJECTIVE RATINGS OF SLEEP INERTIA AND DIM LIGHT MELATONIN ONSET

The timing of work and social requirements has a negative impact on performance and well-being of a significant proportion of the population in our modern society due to a phenomenon known as social jetlag. During workdays, in the early morning, late chronotypes, in particular, suffer from a combination of a nonoptimal circadian phase and sleep deprivation. Sleep inertia, a transient period of lowered arousal after awakening, therefore, becomes more severe. In the present home study, the authors tested whether the use of an alarm clock with artificial dawn could reduce complaints of sleep inertia in people having difficulties in waking up early. The authors also examined whether these improvements were accompanied by a shift in the melatonin rhythm. Two studies were performed: Study 1: three conditions (0, 50, and 250 lux) and Study 2: two conditions (0 lux and self-selected dawn-light intensity). Each condition lasted 2 weeks. In both studies, the use of the artificial dawn resulted in a significant reduction of sleep inertia complaints. However, no significant shift in the onset of melatonin was observed after 2 weeks of using the artificial dawn of 250 lux or 50 lux compared to the control condition. A multilevel analysis revealed that only the presence of the artificial dawn, rather than shift in the dim light melatonin onset or timing of sleep offset, is related to the observed reduction of sleep inertia complaints. Mechanisms other than shift of circadian rhythms are needed to explain the positive results on sleep inertia of waking up with a dawn signal. (Author correspondence: m.c.gimenez@rug.nl)