A compromise circadian phase position for permanent night work improves mood, fatigue, and performance

Circadian adaptation to night shift work is associated with higher REM sleep duration

OBJECTIVE

To investigate the influence of the degree of circadian adaptation to night work on sleep architecture following night shift.

METHODS

Thirty four night workers (11 females; 33.8 ± 10.1years) completed a simulated night shift following 2-7 typical night shifts. Participants completed a laboratory-based simulated night shift (21:00-07:00 hours), followed by a recovery sleep opportunity (∼09:00-17:00 hours), recorded using polysomnography. Urinary 6-sulphatoxymelatonin (aMT6s) rhythm acrophase was used as a marker of circadian phase. Sleep duration and architecture were compared between individuals with aMT6s acrophase before (unadapted group, n = 22) or after (partially adapted group, n = 12) bedtime.

RESULTS

Bedtime occurred on average 2.16 hours before aMT6s acrophase in the partially adapted group and 3.91 hours after acrophase in the unadapted group. The partially adapted group had more sleep during the week before the simulated night than the unadapted group (6.47 ± 1.02 vs. 5.26 ± 1.48 hours, p = .02). After the simulated night shift, both groups had similar total sleep time (partially adapted: 6.68 ± 0.80 hours, unadapted: 6.63 ± 0.88 hours, p > .05). The partially adapted group had longer total rapid eye movement sleep duration than the unadapted group (106.79 ± 32.05 minutes vs. 77.90 ± 28.86 minutes, p = .01). After 5-hours, rapid eye movement sleep accumulation was higher in the partially adapted compared to the unadapted group (p = .02). Sleep latency and other stages were not affected by circadian adaptation.

DISCUSSION

Partial circadian adaptation to night shift was associated with longer rapid eye movement sleep duration during daytime sleep, highlighting the influence of entrainment between the sleep-wake cycle and the circadian pacemaker in night workers. The findings have important implications for sleep and subsequent alertness associated with shift work.

Sex-Dependent Effects of Chronic Circadian Disruption in AβPP/PS1 Mice

BACKGROUND

Chronic disruption of the circadian timing system, often reflected as a loss of restful sleep, also includes myriad other pathophysiological effects.

OBJECTIVE

The current study examined how chronic circadian disruption (CD) could contribute to pathology and rate of progression in the AβPP/PS1 mouse model of Alzheimer's disease (AD).

METHODS

A chronic CD was imposed until animals reached 6 or 12 months of age in AβPP/PS1 and C57BL/6J control mice. Home cage activity was monitored for a period of 3-4 weeks prior to the endpoint along with a single timepoint measure of glucose sensitivity. To assess long term effects of CD on the AD phenotype, animals were re-entrained to a no disruption (ND) schedule just prior to the endpoint, after which a Morris water maze (MWM) was used to assess spatial learning and memory.

RESULTS

Dampening of nighttime activity levels occurred in disrupted animals, and female animals demonstrated a greater adaptability to CD. Diminished arginine vasopressin (AVP) and vasoactive intestinal peptide (VIP) levels in the suprachiasmatic nucleus (SCN) of 12-month male AβPP/PS1 exposed to the CD paradigm were observed, potentially accounting for the diminished re-entrainment response. Similarly, CD worsened performance in the MWM in 12-month male AβPP/PS1 animals, whereas no effect was seen in females.

CONCLUSIONS

Collectively, these findings show that exposure to chronic CD impairs circadian behavioral patterns and cognitive phenotypes of AβPP/PS1 mouse model in a sex-dependent manner.

Time-of-day effects on speed and accuracy performance during simulated shiftwork

Performance on tasks involving speed and accuracy fluctuate throughout the 24-h day negatively affecting shift workers and organizations. Two simulated work shifts common in occupational settings were used to assess performance on a vigilance and math task. In study 1, 33 sleep-deprived participants completed a nightshift. In study 2, 32 partially sleep-deprived participants completed a dayshift. These studies found that performance differed between the type of task and the type of simulated shift where performance during the nightshift was worse than during the dayshift. In addition, collapsing speed and accuracy on the math task into inverse efficiency scores provided a unique measure that captured the impact of circadian rhythms during shiftwork. The current study also indicated that participants adopted cognitive strategies including speed-accuracy tradeoff and regulatory foci regarding work motivation (prevention focus and promotion focus) when completing the tasks depending on time-of-day, type of shift, circadian rhythms, and amount of sleep deprivation. This suggests that researchers and organizations should consider cognitive strategies in addition to the physiological components of sleep deprivation and circadian rhythms when investigating and documenting the impact of time-of-day due to different types of shiftwork conditions on performance and safety.

Emergency Medicine Personnel's Preparation, Performance and Perception of Their Night Shifts: A Cross-Sectional Study from Saudi Arabia

PURPOSE

This study aimed to investigate the perceptions and habits of different emergency department (ED) workers (nurses, residents, and attending physicians) and their pre- or post-shift routines. The study also examined the effect of night shifts on personal life, social life, and health.

PATIENTS AND METHODS

An anonymous, online, cross-sectional, multiple-choice, self-rating (5-point Likert scale) survey was administered to the participants. All analyses were performed using the SPSS version 22.0. Ethical approval was obtained from the Institutional Review Board (IRB) of King Saud University Medical City (KSUMC) in Riyadh, Saudi Arabia.

RESULTS

Thirty-three nurses, 51 residents, and 39 attending physicians participated in the survey (response rates of 21%, 100%, and 100%, respectively). A significant difference was noted in the need to use physical sleeping aids between the three groups (P < 0.003), with more nurses using humidifiers as a sleeping aid (21.2%) than residents or attending physicians. However, there was no difference in the use of pharmacological aids between the three groups. All groups utilized coffee as the preferred stimulant, especially residents (76.5%, P <0.032). Nurses and attending physicians wake up 2 hours before their shift, while residents prefer 3 hours (P <0.001). Attending physicians reported the highest accident rates post-night shifts of 17.9% (P < 0.001). Residents reported satisfaction while working night shifts and were least in agreement with night shifts reducing life span. Attending physicians were more in agreement with the increasing risk of drug/alcohol misuse and the incidence of depression in relation to night shifts.

CONCLUSION

Participants shared many commonalities, yet residents were less likely to use sleeping aids and enjoy night shifts more than the other groups. All groups consumed coffee for stimulation. Attending physicians reported the highest accident rates post night shifts.

Circadian Rhythm Sleep-Wake Disorders

PURPOSE OF REVIEW

This article provides an overview of circadian physiology and discusses common presentations and treatment strategies for the circadian rhythm sleep-wake disorders.

RECENT FINDINGS

Circadian rhythms are present throughout the body, and appreciation for the role that circadian dysregulation plays in overall health is increasing, with mounting associations between circadian disruption and cardiometabolic disease risk.

SUMMARY

It is important to recognize the ubiquitous role that circadian rhythms play throughout the brain and body. An understanding of circadian neurophysiology will provide insight into the means by which patients with a variety of neuropathologies at the level of the retina, optic nerve, or hypothalamus may also be at risk for circadian dysfunction.

Predicting circadian misalignment with wearable technology: validation of wrist-worn actigraphy and photometry in night shift workers

STUDY OBJECTIVES

A critical barrier to successful treatment of circadian misalignment in shift workers is determining circadian phase in a clinical or field setting. Light and movement data collected passively from wrist actigraphy can generate predictions of circadian phase via mathematical models; however, these models have largely been tested in non-shift working adults. This study tested the feasibility and accuracy of actigraphy in predicting dim light melatonin onset (DLMO) in fixed night shift workers.

METHODS

A sample of 45 night shift workers wore wrist actigraphs before completing DLMO in the laboratory (17.0 days ± 10.3 SD). DLMO was assessed via 24 hourly saliva samples in dim light (<10 lux). Data from actigraphy were provided as input to a mathematical model to generate predictions of circadian phase. Agreement was assessed and compared to average sleep timing on non-workdays as a proxy of DLMO. Model code and an open-source prototype assessment tool are available (www.predictDLMO.com).

RESULTS

Model predictions of DLMO showed good concordance with in-lab DLMO, with Lin's concordance coefficient of 0.70, which was twice as high as agreement using average sleep timing as a proxy of DLMO. The absolute mean error of the predictions was 2.88 h, with 76% and 91% of the predictions falling with 2 and 4 h, respectively.

CONCLUSION

This study is the first to demonstrate the use of wrist actigraphy-based estimates of circadian phase as a clinically useful and valid alternative to in-lab measurement of DLMO in fixed night shift workers. Future research should explore how additional predictors may impact accuracy.

Lighting the Patient Room of the Future: Evaluating Different Lighting Conditions for Performing Typical Nursing Tasks

PURPOSE

This study explores how aspects of lighting in patient rooms are experienced and evaluated by nurses while performing simulated work under various lighting conditions. The lighting conditions studied represent design standards consistent with different environments of care-traditional, contemporary, and future.

BACKGROUND

Recent advances in lighting research and technology create opportunities to use lighting in hospital rooms to improve everyday experience and provide researchers with opportunities to explore a new set of research questions about the effects of lighting on patients, guests, and staff. This study focuses on the experience of nurses delivering simulated patient care.

METHOD

Perceptions of each of the 13 lighting conditions were evaluated by nurses using rating scales for difficulty of task completion, comfort, intensity, appropriateness of the lighting color, and naturalness of the lighting during the task. The nurses' ratings were analyzed alongside qualitative reflections to provide insight into their responses.

RESULTS

Significant differences were found for several a priori hypotheses. Interesting findings provide insight into lighting to support circadian synchronization, lighting at night, the distribution of light in the patient room and the use of multiple lighting zones, and the use of colored lighting.

CONCLUSION

The results of this study provide insight into potential benefits and concerns of these new features for patient room lighting systems and reveal gaps in the existing evidence base that can inform future investigations.

Does the compromised sleep and circadian disruption of night and shiftworkers make them highly vulnerable to 2019 coronavirus disease (COVID-19)?

Rotating and permanent night shiftwork schedules typically result in acute and sometimes chronic sleep deprivation plus acute and sometimes chronic disruption of the circadian time structure. Immune system processes and functionalities are organized as circadian rhythms, and they are also strongly influenced by sleep status. Sleep is a vital behavioral state of living beings and a modulator of immune function and responsiveness. Shiftworkers show increased risk for developing viral infections due to possible compromise of both innate and acquired immunity responses. Short sleep and sleep loss, common consequences of shiftwork, are associated with altered integrity of the immune system. We discuss the possible excess risk for COVID-19 infection in the context of the common conditions among shiftworkers, including nurses, doctors, and first responders, among others of high exposure to the contagion, of sleep imbalance and circadian disruption.

ABBREVIATIONS

ACE2: Angiotensin-converting enzyme 2; APC: Antigen.-presenting .cells; CCL: Chemokine (C-C motif) ligand; CD⁺: .Adhesion molecule expression; COVID-19: 2019 coronavirus disease; DCs: Dendritic cells; GH: Growth hormone; HPA: Hypothalamic-pituitary-adrenal; HSF: Heat shock factor; HSP70: Heat shock protein 70; HSP90: Heat shock protein 90; IL: Interleukin; INFγ: Interferon-gamma; LT/LB: T/B lymphocytes; MHC: Major histocompatibility complex; NK: Natural .killer; RAAS: renin-angiotensin-aldosterone system; SARS: .Severe acute respiratory syndrome; SCN: Suprachiasmatic nucleus;SD: Sleep deprivation; SNS: Sympathetic nervous system; Th1/Th2: T helper lymphocytes 1/2; TLR2/TLR4: Toll-like receptor 2/4; TNF-α: Tumor .necrosis .factor alpha; VEGF: Vascular endothelial growth factor.

The Effect of Shift Work and Poor Sleep on Self-Reported Skin Conditions: A Survey of Call Center Agents in the Philippines

Night shift workers may have a disrupted circadian rhythm, which may contribute to the development of skin disease. The purpose of this study was to determine whether there is a significant difference in the prevalence and severity of self-reported skin disease between "regular" day shift workers compared to "graveyard" night shift workers. We conducted surveys from 630 call center agents in Manila, the Philippines, and they were analyzed regarding demographics, medical history, dermatologic history, lifestyle, and sleep. No difference was found in the prevalence of skin disease between shifts. However, night shift workers were worse sleepers. When compared to good sleepers, poor sleepers had a higher prevalence of skin disease with worse severity. Graveyard shift workers with poor sleep may have increased skin disease severity.

Night shift preparation, performance, and perception: are there differences between emergency medicine nurses, residents, and faculty?

Objective

Determine differences between faculty, residents, and nurses regarding night shift preparation, performance, recovery, and perception of emotional and physical health effects.

Methods

Survey study performed at an urban university medical center emergency department with an accredited residency program in emergency medicine.

Results

Forty-seven faculty, 37 residents, and 90 nurses completed the survey. There was no difference in use of physical sleep aids between groups, except nurses utilized blackout curtains more (69%) than residents (60%) and faculty (45%). Bedroom temperature preference was similar. The routine use of pharmacologic sleep aids differed: nurses and residents (both 38%) compared to faculty (13%). Residents routinely used melatonin more (79%) than did faculty (33%) and nurses (38%). Faculty preferred not to eat (45%), whereas residents (24%) preferred a full meal. The majority (>72%) in all groups drank coffee before their night shift and reported feeling tired despite their routine, with 4:00 a.m. as median nadir. Faculty reported a higher rate (41%) of falling asleep while driving compared to residents (14%) and nurses (32%), but the accident rate (3% to 6%) did not differ significantly. All had similar opinions regarding night shift-associated health effects. However, faculty reported lower level of satisfaction working night shifts, whereas nurses agreed less than the other groups regarding increased risk of drug and alcohol dependence.

Conclusion

Faculty, residents, and nurses shared many characteristics. Faculty tended to not use pharmacologic sleep aids, not eat before their shift, fall asleep at a higher rate while driving home, and enjoy night shift work less.

Sleep and cognitive performance of African-Americans and European-Americans before and during circadian misalignment produced by an abrupt 9-h delay in the sleep/wake schedule

We conducted two studies of circadian misalignment in non-Hispanic African and European-Americans. In the first, the sleep/wake (light/dark) schedule was advanced 9 h, similar to flying east, and in the second these schedules were delayed 9 h, similar to flying west or sleeping during the day after night work. We confirmed that the free-running circadian period is shorter in African-Americans compared to European-Americans, and found differences in the magnitude and direction of circadian rhythm phase shifts which were related to the circadian period. The sleep and cognitive performance data from the first study (published in this journal) documented the impairment in both ancestry groups due to this extreme circadian misalignment. African-Americans slept less and performed slightly worse during advanced/misaligned days than European-Americans. The current analysis is of sleep and cognitive performance from the second study. Participants were 23 African-Americans and 22 European-Americans (aged 18-44 years). Following four baseline days (8 h time in bed, based on habitual sleep), the sleep/wake schedule was delayed by 9 h for three days. Sleep was monitored using actigraphy. During the last two baseline/aligned days and the first two delayed/misaligned days, beginning 2 h after waking, cognitive performance was assessed every 3 h using the Automated Neuropsychological Assessment Metrics (ANAM) battery. Mixed model ANOVAs assessed the effects of ancestry (African-American or European-American) and condition (baseline/aligned or delayed/misaligned) on sleep and performance. There was decreased sleep and impaired cognitive performance in both ancestry groups during the two delayed/misaligned days relative to baseline/aligned days. Sleep and cognitive performance did not differ between African-Americans and European-Americans during either baseline/aligned or delayed/misaligned days. While our previous work showed that an advance in the sleep/wake schedule impaired the sleep of African-Americans more than European-Americans, delaying the sleep/wake schedule impaired the sleep and cognitive performance of African-Americans and European-Americans equally.

Advancing the sleep/wake schedule impacts the sleep of African-Americans more than European-Americans

There are differences in sleep duration between Blacks/African-Americans and Whites/European-Americans. Recently, we found differences between these ancestry groups in the circadian system, such as circadian period and the magnitude of phase shifts. Here we document the role of ancestry on sleep and cognitive performance before and after a 9-h advance in the sleep/wake schedule similar to flying east or having a large advance in sleep times due to shiftwork, both of which produce extreme circadian misalignment. Non-Hispanic African and European-Americans (N = 20 and 17 respectively, aged 21-43 years) were scheduled to four baseline days each with 8 h time in bed based on their habitual sleep schedule. This sleep/wake schedule was then advanced 9 h earlier for three days. Sleep was monitored using actigraphy. During the last two baseline/aligned days and the first two advanced/misaligned days, beginning 2 h after waking, cognitive performance was measured every 3 h using the Automated Neuropsychological Assessment Metrics (ANAM) test battery. Mixed model ANOVAs assessed the effects of ancestry (African-American or European-American) and condition (baseline/aligned or advanced/misaligned) on sleep and cognitive performance. There was decreased sleep and impaired performance in both ancestry groups during the advanced/misaligned days compared to the baseline/aligned days. In addition, African-Americans obtained less sleep than European-Americans, especially on the first two days of circadian misalignment. Cognitive performance did not differ between African-Americans and European-Americans during baseline days. During the two advanced/misaligned days, however, African-Americans tended to perform slightly worse compared to European-Americans, particularly at times corresponding to the end of the baseline sleep episodes. Advancing the sleep/wake schedule, creating extreme circadian misalignment, had a greater impact on the sleep of African-Americans than European-Americans. Ancestry differences in sleep appear to be exacerbated when the sleep/wake schedule is advanced, which may have implications for individuals undertaking shiftwork and transmeridian travel.

The NICU Lighted Environment

Lighting technologies are rapidly evolving, creating many opportunities for good lighting within the NICU. With the widespread adoption of advanced solid-state lighting technologies, lighting no longer needs to be static. Rather, lighting systems can be more easily adjusted to the different and changing visual and non-visual needs of the professional staff, infants and family members throughout the 24-hour day. This paper provides a conceptual framework for defining good lighting in the NICU, recognizing the needs of various constituent groups, each with very different needs from the lighting. Several other papers on the topic of lighting for various constituent groups at different times of the day in the NICU are summarized. Attention is given specifically to the Recommended Standards for Newborn ICU Design, a consensus standard developed by a wide range of experts, to help the reader translate this conceptual framework to practice.

Circadian rhythms of European and African-Americans after a large delay of sleep as in jet lag and night work

Jet travel and night shift work produce large changes in when people sleep, work and eat; a challenge that was not encountered during most of our evolution. Successful adaptation would require the internal, master, circadian clock to make large phase shifts to reduce the circadian misalignment between circadian rhythms and the times for sleep, work and meals. We compared African-Americans and non-Hispanic European-Americans in how much their circadian clocks shifted after a 9 hour phase delay of the light/dark, sleep/wake and meal schedule, which has similarities to flying west or sleeping in the daytime after night shifts. We also measured their free-running circadian periods using a forced desynchrony protocol with a 5-h day. European-Americans had longer free-running periods and larger phase delays than African-Americans. Correlations (among all subjects, just African-Americans and just European-Americans) showed that longer circadian periods were associated with larger phase delays. Larger phase delays, facilitated by longer circadian periods, reduce jet lag after westward travel and make it easier to work night shifts and sleep during the daytime after night work. On the other hand, a shorter circadian period, which makes one more of a morning-type person, is better for most people given our early-bird dominated society.

Sleep, immunity and shift workers: A review

To date, shift workers represent between 15% and 25% of the modern day workforce. Work time poses a great challenge to workers as it requires that they balance productivity and sleep time between shifts. As a result, these workers experience chronic sleep deprivation with increased fatigue and drowsiness due to this sleep deprivation. The impact of this kind of work on the immune system is not yet known. We conducted a literature review with the aim of evaluating articles on this specific type of work's effects on sleep and immunity.

Circadian Rhythm Sleep-Wake Disorders

The circadian system regulates the timing and expression of nearly all biological processes, most notably, the sleep-wake cycle, and disruption of this system can result in adverse effects on both physical and mental health. The circadian rhythm sleep-wake disorders (CRSWDs) consist of 5 disorders that are due primarily to pathology of the circadian clock or to a misalignment of the timing of the endogenous circadian rhythm with the environment. This article outlines the nature of these disorders, the association of many of these disorders with psychiatric illness, and available treatment options.

Phase advancing human circadian rhythms with morning bright light, afternoon melatonin, and gradually shifted sleep: can we reduce morning bright-light duration?

OBJECTIVE

Efficient treatments to phase-advance human circadian rhythms are needed to attenuate circadian misalignment and the associated negative health outcomes that accompany early-morning shift work, early school start times, jet lag, and delayed sleep phase disorder. This study compared three morning bright-light exposure patterns from a single light box (to mimic home treatment) in combination with afternoon melatonin.

METHODS

Fifty adults (27 males) aged 25.9 ± 5.1 years participated. Sleep/dark was advanced 1 h/day for three treatment days. Participants took 0.5 mg of melatonin 5 h before the baseline bedtime on treatment day 1, and an hour earlier each treatment day. They were exposed to one of three bright-light (~5000 lux) patterns upon waking each morning: four 30-min exposures separated by 30 min of room light (2-h group), four 15-min exposures separated by 45 min of room light (1-h group), and one 30-min exposure (0.5-h group). Dim-light melatonin onsets (DLMOs) before and after treatment determined the phase advance.

RESULTS

Compared to the 2-h group (phase shift = 2.4 ± 0.8 h), smaller phase-advance shifts were seen in the 1-h (1.7 ± 0.7 h) and 0.5-h (1.8 ± 0.8 h) groups. The 2-h pattern produced the largest phase advance; however, the single 30-min bright-light exposure was as effective as 1 h of bright light spread over 3.25 h, and it produced 75% of the phase shift observed with 2 h of bright light.

CONCLUSIONS

A 30-min morning bright-light exposure with afternoon melatonin is an efficient treatment to phase-advance human circadian rhythms.

Daytime light exposure: effects on biomarkers, measures of alertness, and performance

Light can elicit an alerting response in humans, independent from acute melatonin suppression. Recent studies have shown that red light significantly increases daytime and nighttime alertness. The main goal of the present study was to further investigate the effects of daytime light exposure on performance, biomarkers and measures of alertness. It was hypothesized that, compared to remaining in dim light, daytime exposure to narrowband long-wavelength (red) light or polychromatic (2568K) light would induce greater alertness and shorter response times. Thirteen subjects experienced three lighting conditions: dim light (<5lux), red light (λmax=631nm, 213lux, 1.1W/m(2)), and white light (2568K, 361lux, 1.1W/m(2)). The presentation order of the lighting conditions was counterbalanced across the participants and each participant saw a different lighting condition each week. Our results demonstrate, for the first time, that red light can increase short-term performance as shown by the significant (p<0.05) reduced response time and higher throughput in performance tests during the daytime. There was a significant decrease (p<0.05) in alpha power and alpha-theta power after exposure to the white light, but this alerting effect did not translate to better performance. Alpha power was significantly reduced after red light exposure in the middle of the afternoon. There was no significant effect of light on cortisol and alpha amylase. The present results suggest that red light can be used to increase daytime performance.

Circadian adaptation to night shift work influences sleep, performance, mood and the autonomic modulation of the heart

Our aim was to investigate how circadian adaptation to night shift work affects psychomotor performance, sleep, subjective alertness and mood, melatonin levels, and heart rate variability (HRV). Fifteen healthy police officers on patrol working rotating shifts participated to a bright light intervention study with 2 participants studied under two conditions. The participants entered the laboratory for 48 h before and after a series of 7 consecutive night shifts in the field. The nighttime and daytime sleep periods were scheduled during the first and second laboratory visit, respectively. The subjects were considered "adapted" to night shifts if their peak salivary melatonin occurred during their daytime sleep period during the second visit. The sleep duration and quality were comparable between laboratory visits in the adapted group, whereas they were reduced during visit 2 in the non-adapted group. Reaction speed was higher at the end of the waking period during the second laboratory visit in the adapted compared to the non-adapted group. Sleep onset latency (SOL) and subjective mood levels were significantly reduced and the LF∶HF ratio during daytime sleep was significantly increased in the non-adapted group compared to the adapted group. Circadian adaptation to night shift work led to better performance, alertness and mood levels, longer daytime sleep, and lower sympathetic dominance during daytime sleep. These results suggest that the degree of circadian adaptation to night shift work is associated to different health indices. Longitudinal studies are required to investigate long-term clinical implications of circadian misalignment to atypical work schedules.

Circadian and behavioural responses to shift work-like schedules of light/dark in the mouse

Background

Disruption of circadian rhythms is associated with several deleterious health consequences and cognitive impairment. It is estimated that as many as one in five workers are exposed to this risk factor due to experiencing some degree of chronodisruption by way of recurring patterns of shift work. It is not presently clear therefore how efficiently the mammalian circadian system entrains to alternative light/dark cycles such as those found in shift work schedules.

Methods

The present study examines male CD-1 mice exposed to three different paradigms of rapidly rotating shift work-like light/dark manipulations compared to control animals maintained on a standard 12:12 h light/dark cycle.

Results

Analysis of circadian patterns of behaviour under such conditions reveals that for fast rotating schedules of light/dark there is minimal circadian entrainment. Further, when placed in constant conditions after a period under the “shift work” lighting conditions there were changes to circadian period associated with the shift work schedules. In contrast to previous studies the shift work-like conditions did not produce changes in animal body-weight. Behavioural testing suggests possible anxiogenic and hyperactive outcomes dependent on rotation speed as animals displayed open field thigmotaxis and hyperlocomotion.

Conclusion

These results indicate that exposure to alternating patterns of light and dark as experienced by millions of shift workers may produce long-lasting changes in both mammalian circadian and neurobehavioural systems.

Metabolism as an integral cog in the mammalian circadian clockwork

Circadian rhythms are an integral part of life. These rhythms are apparent in virtually all biological processes studies to date, ranging from the individual cell (e.g. DNA synthesis) to the whole organism (e.g. behaviors such as physical activity). Oscillations in metabolism have been characterized extensively in various organisms, including mammals. These metabolic rhythms often parallel behaviors such as sleep/wake and fasting/feeding cycles that occur on a daily basis. What has become increasingly clear over the past several decades is that many metabolic oscillations are driven by cell-autonomous circadian clocks, which orchestrate metabolic processes in a temporally appropriate manner. During the process of identifying the mechanisms by which clocks influence metabolism, molecular-based studies have revealed that metabolism should be considered an integral circadian clock component. The implications of such an interrelationship include the establishment of a vicious cycle during cardiometabolic disease states, wherein metabolism-induced perturbations in the circadian clock exacerbate metabolic dysfunction. The purpose of this review is therefore to highlight recent insights gained regarding links between cell-autonomous circadian clocks and metabolism and the implications of clock dysfunction in the pathogenesis of cardiometabolic diseases.

Health consequences of shift work and implications for structural design

The objective of the study was to perform a literature review on the health consequences of working rotating shifts and implications for structural design. A literature search was performed in June 2012 and a selection of the most relevant peer-review articles was included in the present review. Shift workers are more likely to suffer from a circadian sleep disorder characterized by sleepiness and insomnia. Shift work is associated with decreased productivity, impaired safety, diminished quality of life and adverse effects on health. Circadian disruption resulting from rotating shift work has also been associated with increased risk for metabolic syndrome, diabetes, cardiovascular disease and cancer. This article summarizes the known health effects of shift work and discusses how light can be used as a countermeasure to minimize circadian disruption at night while maintaining alertness. In the context of the lighted environment, implications for the design of newborn intensive care units are also discussed.

Shift work: health, performance and safety problems, traditional countermeasures, and innovative management strategies to reduce circadian misalignment

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.

Shift work and the assessment and management of shift work disorder (SWD)

Nearly 20% of the labor force worldwide, work shifts that include work hours outside 07:00 h to 18:00 h. Shift work is common in many occupations that directly affect the health and safety of others (e.g., protective services, transportation, healthcare), whereas quality of life, health, and safety during shift work and the commute home can affect workers in any field. Increasing evidence indicates that shift-work schedules negatively influence worker physiology, health, and safety. Shift work disrupts circadian sleep and alerting cycles, resulting in disturbed daytime sleep and excessive sleepiness during the work shift. Moreover, shift workers are at risk for shift work disorder (SWD). This review focuses on shift work and the assessment and management of sleepiness and sleep disruption associated with shift work schedules and SWD. Management strategies include approaches to promote sleep, wakefulness, and adaptation of the circadian clock to the imposed work schedule. Additional studies are needed to further our understanding of the mechanisms underlying the health risks of shift work, understanding which shift workers are at most risk of SWD, to investigate treatment options that address the health and safety burdens associated with shift work and SWD, and to further develop and assess the comparative effectiveness of countermeasures and treatment options.

Treatment of shift work disorder and jet lag

OPINION STATEMENT

With the growth of the 24-hour global marketplace, a substantial proportion of workers are engaged in nontraditional work schedules and frequent jet travel across multiple time zones. Thus, shift work disorder and jet lag are prevalent in our 24/7 society and have been associated with significant health and safety repercussions. In both disorders, treatment strategies are based on promoting good sleep hygiene, improving circadian alignment, and targeting specific symptoms.Treatment of shift work must be tailored to the type of shift. For a night worker, circadian alignment can be achieved with bright light exposure during the shift and avoidance of bright light (with dark or amber sunglasses) toward the latter portion of the work period and during the morning commute home. If insomnia and/or excessive sleepiness are prominent complaints despite behavioral approaches and adequate opportunity for sleep, melatonin may be administered prior to the day sleep period to improve sleep, and alertness during work can be augmented by caffeine and wake-promoting agents.For jet lag, circadian adaptation is suggested only for travel greater than 48 h, with travel east more challenging than travel west. Although advancing sleep and wake times and circadian timing for eastward travel with evening melatonin and morning bright light several days prior to departure can help avoid jet lag at the new destination, this approach may be impractical for many people, Therefore, strategies for treatment at the destination, such as avoidance of early morning light and exposure to late-morning and afternoon light alone or in conjunction with bedtime melatonin, can accelerate re-entrainment following eastward travel. For westward travel, a circadian delay can be achieved after arrival with afternoon and early-evening light with bedtime melatonin.Good sleep hygiene practices, together with the application of circadian principles, can improve sleep quality, alertness, performance, and safety in shift workers and jet travelers. However, definitive multicenter randomized controlled clinical trials are still needed, using traditional efficacy outcomes such as sleep and performance as well as novel biomarkers of health.

Spectral modulation attenuates molecular, endocrine, and neurobehavioral disruption induced by nocturnal light exposure

The human eye serves distinctly dual roles in image forming (IF) and non-image-forming (NIF) responses when exposed to light. Whereas IF responses mediate vision, the NIF responses affect various molecular, neuroendocrine, and neurobehavioral variables. NIF responses can have acute and circadian phase-shifting effects on physiological variables. Both the acute and phase-shifting effects induced by photic stimuli demonstrate short-wavelength sensitivity peaking ≈450-480 nm. In the current study, we examined the molecular, neuroendocrine, and neurobehavioral effects of completely filtering (0% transmission) all short wavelengths <480 nm and all short wavelengths <460 nm or partially filtering (~30% transmission) <480 nm from polychromatic white light exposure between 2000 and 0800 in healthy individuals. Filtering short wavelengths <480 nm prevented nocturnal light-induced suppression of melatonin secretion, increased cortisol secretion, and disrupted peripheral clock gene expression. Furthermore, subjective alertness, mood, and errors on an objective vigilance task were significantly less impaired at 0800 by filtering wavelengths <480 nm compared with unfiltered nocturnal light exposure. These changes were not associated with significantly increased sleepiness or fatigue compared with unfiltered light exposure. The changes in molecular, endocrine, and neurobehavioral processes were not significantly improved by completely filtering <460 nm or partially filtering <480 nm compared with unfiltered nocturnal light exposure. Repeated light-dark cycle alterations as in rotating nightshifts can disrupt circadian rhythms and induce health disorders. The current data suggest that spectral modulation may provide an effective method of regulating the effects of light on physiological processes.

Using blue-green light at night and blue-blockers during the day to improves adaptation to night work: a pilot study

BACKGROUND

Bright light at night paired with darkness during the day seem to facilitate adaptation to night work. Considering the biological clock sensitive to short wavelengths, we investigated the possibility of adaptation in shift workers exposed to blue-green light at night, combined with using blue-blockers during the day.

METHODS

Four sawmill shift workers were evaluated during two weeks of night shifts (control and experimental) and one week of day shifts. Throughout the experimental week, ambient light (approximately 130 lx) was supplemented with blue-green light (200 lx) from 00:00 h to: 05:00 h on Monday and Tuesday, 06:00 h on Wednesday and 07:00 h on Thursday. Blue-blockers had to be worn outside from the end of the night shift until 16:00 h. For circadian assessment, salivary melatonin profiles were obtained between 00:00 h and 08:00 h, before and after 4 experimental night shifts. Sleep was continuously monitored with actigraphy and subjective vigilance was measured at the beginning, the middle and the end of each night and day shifts. The error percentage in wood board classification was used as an index of performance.

RESULTS

Through experimental week, melatonin profiles of 3 participants have shifted by at least 2 hours. Improvements were observed in sleep parameters and subjective vigilance from the third night (Wednesday) as performance increased on the fourth night (Thursday) from 5.14% to 1.36% of errors (p=0.04).

CONCLUSIONS

Strategic exposure to short wavelengths at night, and/or daytime use of blue-blocker glasses, seemed to improve sleep, vigilance and performance.