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Abstract Sleep loss is one of the most common causes of accidents and errors in operational environments. Currently, no single method satisfies all of the requisite criteria of an effective system for assessing the risk of injury prior to safety being compromised. Research has concentrated towards the development of a biomarker for individualized assessment of sleepiness-related deficits in neurobehavioral alertness, with salivary alpha-amylase (sAA) recently reported as a potential biomarker during acute total sleep deprivation. The present study extends on previous research by investigating the association between sAA and neurobehavioral alertness during simulated night-shift work, during individuals are required to work at night when biological processes are strongly promoting sleep and sleep during the day when endogenous processes are promoting wakefulness. In a laboratory-controlled environment, 10 healthy non-shift working males aged 24.7 ± 5.3 years (mean ± SD) underwent four consecutive nights of simulated night-shift work. Between 17:30–04:30 h participants provided saliva samples and completed a 3 min psychomotor vigilance test (PVT-B), 40 min simulated driving task, and 3 min digit symbol substitution test (DSST). Higher sAA levels were associated with faster response speed on the PVT-B, reduced lane variability on the simulated driving task, and improved information processing speed on the DSST during the first night-shift. There were no associations between sAA levels and performance outcomes during subsequent night-shifts. Findings indicate that the usability of sAA to assess the risk of neurobehavioral deficits during shift-work operations is limited. However, the robust circadian rhythm exhibited by sAA during the protocol of circadian misalignment suggests that sAA could serve as a potential circadian marker. Highlights • Salivary alpha-amylase levels predict alertness during total sleep deprivation • Salivary alpha-amylase levels do not predict alertness during night-shift work. • Circadian rhythm of salivary alpha-amylase is robust. • Salivary levels of alpha-amylase may serve as an adjunct circadian marker [ABSTRACT FROM AUTHOR]

Abstract Adult Nothobranchius furzeri of the MZM-04/10 strain were individually kept and subjected to a "5 + 2" shifting lighting schedule (SHIFT) for 8 weeks in order to evaluate the desynchronizing effects of a simulated human-like shift-work schedule on the functioning of the circadian system (CS). With this aim, sixteen 21-week-old N. furzeri were placed into a Morning, Night and Evening schedule (lights on from 08:00 to 16:00, 00:00 to 08:00 and 16:00 to 00:00 h, respectively) and fed once a day in the middle of the corresponding photophase (12:00, 04:00 and 20:00 h, respectively). Then, in the weekends (2 days), fish were always returned to the Morning shift. As controls, 16 fish were maintained under a non-shifting LD cycle condition (CONTROL) throughout the whole experiment, with lights on from 08:00 to 16:00 h. Rest-activity rhythm (RAR) of fish subjected to SHIFT showed several symptoms of chronodisruption, such as a decrease in the percentage of diurnal activity and a reduction of the relative amplitude and the circadian function index with time. When a periodogram analysis was performed, RAR of N. furzeri under SHIFT conditions showed up to three separate circadian components: one longer than 24 h (26.5 h) that followed the weekly 8 h delays; a short-period component (~23 h) that was related to the weekend's phase advances, and finally, a 24 h component. The shifting LD schedule also affected fish CS at a molecular level, with several significant differences in the expression of core genes of the molecular clock (bmal1 , clock , rorα , rev - erbα) between SHIFT and CONTROL animals. RAR impairment along with changes in clock gene expression could be associated with high stress and accelerated aging in these fish. Highlights • This study proposes for the first time the use of a "5+2" shifting light-dark schedule on a diurnal vertebrate model; • Rest-activity rhythm of fish subjected to a shifting light-dark schedule showed several symptoms of chronodisruption; • The shifting light-dark schedule affected fish circadian system at a molecular level; • We found several differences in the expression of core genes of the molecular clock between control and shift animals. [ABSTRACT FROM AUTHOR]

Disturbed light–dark (LD) cycles are associated with circadian disruption of physiological and behavioural rhythms and in turn with an increased risk of disease development. However, direct causal links and underlying mechanisms leading to negative health consequences still need to be revealed. In the present study, we exposed male Wistar rats to repeated phase shifts of LD cycle and analysed their ability to cope with mild emotional stressors. In experiment 1, rats were submitted to either a regular 12:12 LD cycle (CTRL rats) or 8-h phase delay shifts applied every 2 days for 5 weeks (SHIFT rats). Subsequently, the behaviour was examined in the open-field, black–white box and elevated plus maze tests. In experiment 2, changes in blood pressure (BP), heart rate (HR) as well as the activity of autonomic nervous system were measured in telemeterised rats in response to open-field and black–white box tests before and after 5-week exposure to shifted LD regime. Locomotor activity was consistently higher in SHIFT than CTRL rats in in the open-field and black–white box tests. Interestingly, in the elevated plus maze, SHIFT rats displayed increased risk assessment and decreased grooming compared to CTRL rats. Anxiety measures were affected only in the black–white box, where SHIFT rats displayed reduced anxiety-like behaviour compared to CTRL rats. Differences in behavioural reactivity between SHIFT and CTRL rats did not correspond with BP and HR changes. However, exposure to phase shifts increased the sympathovagal reactivity in the black–white box. Together, our results demonstrated that disturbed LD conditions decreased emotional reactivity of rats and affected their ability to cope with emotional stressors denoting an additional risk mechanism linking disrupted circadian organisation to adverse health effects. [ABSTRACT FROM AUTHOR]

Background: Obesity is associated with productivity loss, but little is known about how obese workers function at work and also the role of working-time arrangements on this association is lacking. Therefore, the aim of this study was to examine the association of overweight and obesity with work functioning (WF), and to determine whether the associations differ between workers with different working-time arrangements.Methods: A cross-sectional study was conducted within the sampling frame of the 'Shift Your Work' study that examined the effect of irregular working-times in relation to health and functioning at work. We included N = 622 Dutch employees, of which N = 384 (62%) were shift-workers, N = 171 (27%) on-call workers and N = 67 (11%) day-workers. Overweight and obesity were defined as BMI 25-30 and ≥30, respectively. WF was assessed using the Work-Role Functioning Questionnaire.Results: The prevalences of overweight and obesity were 48% and 10% in all workers, 49% and 11% in shift-workers, 45% and 10% in on-call workers, and 49% and 6% in day workers, respectively. In all workers, obesity was associated with lower WF scores for physical demands (adjusted estimate, aB = -5.5). In shift-workers, obesity was associated with lower WF scores for output and physical demands (aB = -8.8 and -6.8, respectively). In day and on-call workers, overweight and obesity were not associated with WF.Conclusions: Overweight and obesity are highly prevalent in the working population. Obesity might reduce the executive function performance beyond physical limitations, and limit the ability to accomplish tasks successfully, especially in shift workers. [ABSTRACT FROM AUTHOR]

Highlights: [•] Environmental perturbations in circadian rhythm may increase the risk of selected cancers. [•] Physiologic and cellular molecular clocks exist. [•] Molecular clocks interact with the cell cycle. [•] Theoretically novel compounds that affect the molecular clock may be used to treat cancer or ameliorate cancer risk. [Copyright &y& Elsevier]

Abstract: By the end of the first night on a 12h night-shift, wakefulness may have lasted up to 24h since the previous sleep. Although most work situations requiring critical decisions are foreseen and effectively resolved by well trained staff, such wakefulness can produce impairments in dealing with unexpected challenging situations involving uncertainty, change, distractions and capacity to evaluate risks. Also compromised can be the ability to engage in and keep abreast of protracted negotiations undertaken throughout the night. These effects, which are not just ‘sleepiness’, seem due to deteriorations with ‘supervisory executive functions’ of the prefrontal cortex; a region that appears particularly vulnerable to prolonged wakefulness. Recent research findings are presented to support this case, and some evidence-based recommendations made about practical countermeasures. [Copyright &y& Elsevier]

Abstract: Background: Working outside normal daytime hours is increasing worldwide and is now one of the most widespread potential carcinogenic occupational exposures. There is sufficient evidence in experimental animals that light exposure during the biologic night increases tumour growth and limited epidemiologic evidence that night shift-work cause breast cancer. Existing studies had crude definitions of shift-work and did not discriminate between shift-work systems (e.g. permanent versus rotating or evening versus night). Methods: We performed an interview based nested case–control study within a nationwide cohort of Danish nurses, including detailed information on lifetime shift-work and potential confounders. Cases of primary breast cancer (n =310) were identified from the nationwide Danish Cancer Registry. Four control nurses were selected for each case by incidence density sampling. Odds rations (ORs) and 95% confidence intervals (CIs) were estimated by conditional logistic regression, with adjustment for potential confounders. Findings: Overall, nurses who worked rotating shifts after midnight had a significantly increased OR (1.8; CI 1.2–2.8) for breast cancer compared to nurses with permanent day work. No association was found in a small group of nurses with evening work and no night work (OR=0.9; 0.4–1.9). The subgroup of nurses with periods of permanent night shift in addition to rotating night and day shifts experienced an OR of 2.9 (1.1–8.0). For nurses working after midnight compared to nurses never ending work before midnight, OR in the third tertile of cumulative number of shifts was 2.2 (1.5–3.2). In an analysis of different rotating shift systems, the highest OR (2.6; 1.8–3.8) was observed for long-term day–night rotating shifts. Interpretation: The results provide further evidence that night shift-work may increase the risk for breast cancer and suggest that the largest impact on risk is associated with the most disruptive shifts. Funding: Danish Cancer Society and National Programme of Environmental Health Research. [Copyright &y& Elsevier]

Abstract: Levels of numerous hormones vary across the day and night. Such fluctuations are not only attributable to changes in sleep/wakefulness and other behaviors but also to a circadian timing system governed by the suprachiasmatic nucleus of the hypothalamus. Sleep has a strong effect on levels of some hormones such as growth hormone but little effect on others which are more strongly regulated by the circadian timing system (e.g., melatonin). Whereas the exact mechanisms through which sleep affects circulating hormonal levels are poorly understood, more is known about how the circadian timing system influences the secretion of hormones. The suprachiasmatic nucleus exerts its influence on hormones via neuronal and humoral signals but it is now also apparent that peripheral tissues contain circadian clock proteins, similar to those in the suprachiasmatic nucleus, that are also involved in hormone regulation. Under normal circumstances, behaviors and the circadian timing system are synchronized with an optimal phase relationship and consequently hormonal systems are exquisitely regulated. However, many individuals (e.g., shift-workers) frequently and/or chronically undergo circadian misalignment by desynchronizing their sleep/wake and fasting/feeding cycle from the circadian timing system. Recent experiments indicate that circadian misalignment has an adverse effect on metabolic and hormonal factors such as circulating glucose and insulin. Further research is needed to determine the underlying mechanisms that cause the negative effects induced by circadian misalignment. Such research could aid the development of novel countermeasures for circadian misalignment. [Copyright &y& Elsevier]

When entering the job market, nurses choose among different kind of jobs. Each of these jobs is characterized by wage, sector (primary care or hospital) and shift (daytime work or shift). This paper estimates a multi-sector-job-type random utility model of labor supply on data for Norwegian registered nurses (RNs) in 2000. The empirical model implies that labor supply is rather inelastic; 10% increase in the wage rates for all nurses is estimated to yield 3.3% increase in overall labor supply. This modest response shadows for much stronger inter-job-type responses. Our approach differs from previous studies in two ways: First, to our knowledge, it is the first time that a model of labor supply for nurses is estimated taking explicitly into account the choices that RN's have regarding work place and type of job. Second, it differs from previous studies with respect to the measurement of the compensations for different types of work. So far, it has been focused on wage differentials. But there are more attributes of a job than the wage. Based on the estimated random utility model we therefore calculate the expected value of compensation that makes a utility maximizing agent indifferent between types of jobs, here between shift work and daytime work. It turns out that Norwegian nurses working shifts may be willing to work shift relative to daytime work for a lower wage than the current one. [Copyright &y& Elsevier]

Nurses function at the point of care and assume a significant role in intercepting errors. They work in a mentally and physically demanding profession that is comprised of shift-work, subjecting nurses to considerable fatigue. Yet, few studies constructed a comprehensive model that integrates personal and occupational factors to explore their relationship with various types of fatigue (acute, chronic, physical, mental, and total). Here, we examine this type of comprehensive fatigue-model, in a report that represents one aim of a larger, mixed-methods study. The study sample comprised of 1137 registered nurses working in eight hospitals in a Midwestern state. Nurses reported higher levels of acute and total fatigue than chronic and physical fatigue. Staffing and resource adequacy, exercise, and sleep were among the strongest predictors. Since fatigue is a multi-faceted construct, a comprehensive fatigue-management strategy that targets both day and night-shift nurses is the optimal way to manage nurse fatigue. [ABSTRACT FROM AUTHOR]

Abstract: Sleep–waking cycles are fundamental in human circadian rhythms and their disruption can have consequences for behaviour and performance. Such disturbances occur due to domestic or occupational schedules that do not permit normal sleep quotas, rapid travel across multiple meridians and extreme athletic and recreational endeavours where sleep is restricted or totally deprived. There are methodological issues in quantifying the physiological and performance consequences of alterations in the sleep–wake cycle if the effects on circadian rhythms are to be separated from the fatigue process. Individual requirements for sleep show large variations but chronic reduction in sleep can lead to immuno-suppression. There are still unanswered questions about the sleep needs of athletes, the role of ‘power naps’ and the potential for exercise in improving the quality of sleep. [Copyright &y& Elsevier]

Abstract: Individuals who work irregular or rotating shifts often use stimulants and sedatives to offset shift-change-related mood and performance decrements. During this simulated shift work study the acute effects of the stimulant, methamphetamine were examined, and the effects of the hypnotic, zolpidem, and the combination were assessed during the shift after drug administration. Eight volunteers completed this 21-day, within-participant, residential laboratory study during which they received a single oral methamphetamine dose (0 or 10 mg) 1 h after waking, i.e., before task performance, and a single oral zolpidem dose (0 or 10 mg) 1 h before bedtime under 2 shift conditions: day shift and night shift. When participants received placebo at both dosing times, performance on some psychomotor tasks (e.g., the digit-symbol substitution task) and on some measures of mood (e.g., ratings of “Energetic”) were disrupted during the night shift, relative to the day shift. Methamphetamine alone eliminated virtually all shift-related disruptions, while zolpidem alone and the drug combination produced few effects. These data indicate that shift changes produce performance impairments and mood alterations that are improved by a single low to moderate dose of methamphetamine. Zolpidem, given alone or in combination with methamphetamine, did not alleviate most shift-change mood and performance effects. [Copyright &y& Elsevier]

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Employing a field-based monitoring paradigm, the current study examined day-to-day fluctuations in actigraphy-based sleep recordings, cognitive performance (10-min psychomotor vigilance test; PVT), and self-reported recovery status among 14 submariners throughout a 67-day military mission. Mission averages reflected suboptimal sleep that was of short overall duration (5:46 ± 1:29 h per 24-h day) and relatively low efficiency (82.5 ± 9.9%); suboptimal levels of cognitive performance (PVT mRT = 283 ± 35 ms; PVT response errors = 5.3 ± 4.8); and moderate levels of self-reported recovery. Whilst self-reported recovery status remained stable across mission days, small but consistent day-to-day increases in sleep onset latency and PVT mRT accumulated to reflect meaningful deterioration in sleep and cognitive performance across the entire 67-day mission (i.e., 47% and 16% of the overall mission average, respectively). Future work is required to corroborate the current findings, firmly establish underlying causes, and make evidence-based suggestions for interventions to improve and uphold submariners' health and performance. [ABSTRACT FROM AUTHOR]

Almost all forms of life have predictable daily or circadian rhythms in molecular, endocrine, and behavioral functions. In mammals, a central pacemaker located in the suprachiasmatic nuclei coordinates the timing of these rhythms. Daily light exposure that affects the retina of the eye directly influences this area, which is required to align endogenous processes to the appropriate time of day. The present "Views and Reviews" articles discuss the influence of circadian rhythms, especially nightly secretion of melatonin, on reproductive function and parturition. In addition, an examination is made of problems that arise from recurrent circadian rhythm disruption associated with changes in light exposure patterns common to modern day society. Finally, a possible solution to prevent disruptions in circadian phase markers by filtering out short wavelengths from nocturnal light is reviewed. [ABSTRACT FROM AUTHOR]