Shift work: Coping with the biological clock

Centre for Chronobiology, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK.
Occupational Medicine (Impact Factor: 1.03). 01/2010; 60(1):10-20. DOI: 10.1093/occmed/kqp162
Source: PubMed


The internal circadian clock adapts slowly, if at all, to rapid transitions between different shift schedules. This leads to misalignment (desynchrony) of rhythmic physiological systems, such as sleep, alertness, performance, metabolism and the hormones melatonin and cortisol, with the imposed work-rest schedule. Consequences include sleep deprivation and poor performance. Clock gene variants may influence tolerance of sleep deprivation. Shift work is associated with an increased risk of major disease (heart disease and cancer) and this may also, at least in part, be attributed to frequent circadian desynchrony. Abnormal metabolism has been invoked as a contributory factor to the increased risk of heart disease. There is recent evidence for an increased risk of certain cancers, with hypothesized causal roles of light at night, melatonin suppression and circadian desynchrony. Various strategies exist for coping with circadian desynchrony and for hastening circadian realignment (if desired). The most important factor in manipulating the circadian system is exposure to and/or avoidance of bright light at specific times of the 'biological night'.

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    • "One exception is number of nights worked the last year, where nurses with SWD worked on average nearly 32 nights per year, while the nurses without SWD worked about 22 nights per year. Also, morning types are reported to have more difficulties adjusting their circadian rhythms to night work [29]. However, in this study the nurses with SWD scored lower on the morningness dimension compared to the nurses with SWD. "
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    ABSTRACT: Background Shift work is associated with sleep problems and impaired health. The main aim of the present study was to explore predictors of developing shift work disorder (SWD) among Norwegian nurses using a longitudinal design. Methods A total of 1533 nurses participating in a survey on shift work, sleep and health responded to questionnaires at baseline and about two years later at follow-up. SWD was defined as problems of excessive sleepiness and/or complaints of insomnia related to the work schedule. Results and Conclusions There was a significant reduction (p<.001) in the prevalence of SWD from baseline to follow-up, from 35.7% to 28.6%. Logistic regression analyses showed significant risks of having SWD at follow-up and the following variables measured at baseline; number of nights worked the last year (OR=1.01, 95% CI=1.01-1.02), having SWD (OR=5.19, 95% CI=3.74-7.20), composite score on the Epworth Sleepiness Scale (OR=1.08, 95% CI=1.04-1.13), use of melatonin (OR=4.20, 95% CI=1.33-13.33), use of bright light therapy (OR=3.10, 95% CI 1.14-8.39), and symptoms of depression measured by the Hospital Anxiety and Depression Scale (OR=1.07, 95% CI=1.00-1.14). In addition, leaving night work between baseline and follow-up was associated with a significant reduced risk of SWD at follow-up (OR=0.12, 95% CI=0.07-0.22).
    Full-text · Article · Sep 2014 · Sleep Medicine
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    • "Alterations in circadian clocks via genetic circadian disruption [15] or circadian desynchrony [16] (defined as modified phase relationships among internal biological rhythms or between internal rhythms and the external environment) are associated with the development of a number of diseases. These include, but are not limited to, cancer [17], metabolic syndrome [9], [15], diabetes [18] and cardiovascular disease [19]. "
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    ABSTRACT: Chronic ethanol consumption disrupts several metabolic pathways including β-oxidation and lipid biosynthesis, facilitating the development of alcoholic fatty liver disease. Many of these same metabolic pathways are directly regulated by cell autonomous circadian clocks, and recent studies suggest that disruption of daily rhythms in metabolism contributes to multiple common cardiometabolic diseases (including non-alcoholic fatty liver disease). However, it is not known whether ethanol disrupts the core molecular clock in the liver, nor whether this, in turn, alters rhythms in lipid metabolism. Herein, we tested the hypothesis that chronic ethanol consumption disrupts the molecular circadian clock in the liver and potentially changes the diurnal expression patterns of lipid metabolism genes. Consistent with previous studies, male C57BL/6J mice fed an ethanol-containing diet exhibited higher levels of liver triglycerides compared to control mice, indicating hepatic steatosis. Further, the diurnal oscillations of core clock genes (Bmal1, Clock, Cry1, Cry2, Per1, and Per2) and clock-controlled genes (Dbp, Hlf, Nocturnin, Npas2, Rev-erbα, and Tef) were altered in livers from ethanol-fed mice. In contrast, ethanol had only minor effects on the expression of core clock genes in the suprachiasmatic nucleus (SCN). These results were confirmed in Per2(Luciferase) knock-in mice, in which ethanol induced a phase advance in PER2::LUC bioluminescence oscillations in liver, but not SCN. Further, there was greater variability in the phase of PER2::LUC oscillations in livers from ethanol-fed mice. Ethanol consumption also affected the diurnal oscillations of metabolic genes, including Adh1, Cpt1a, Cyp2e1, Pck1, Pdk4, Ppargc1a, Ppargc1b and Srebp1c, in the livers of C57BL/6J mice. In summary, chronic ethanol consumption alters the function of the circadian clock in liver. Importantly, these results suggest that chronic ethanol consumption, at levels sufficient to cause steatosis, disrupts the core hepatic clock as well as the diurnal rhythms of key lipid metabolism genes.
    Full-text · Article · Aug 2013 · PLoS ONE
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    • "More importantly, sickness absence may be an important and convenient index of workers' morbidity or general wellbeing (Alexopoulos et al., 2008; Kivimäki et al., 2003; Labriola, 2008; Luz & Green, 1997; Vahtera et al., 2004) but it is not a simple function of ill-health (Duijts et al., 2007; Eriksen et al., 2003). It is commonly hypothesized that shiftwork is linked to sick leave absence via disruption of the sleep-wake cycle and other important biological rhythms (e.g., hormones such as melatonin and cortisol, alertness, performance, body temperature, and metabolism), which consequently leads to increased chronic health problems (e.g., CVD, diabetes, metabolic syndrome, cancer, stomach problems) or injury (Andrzejczak et al., 2011; Arendt, 2010; Kaerlev et al., 2004). However, whether or not shiftwork causes more sickness absence is unclear and the underlying causal pathway is uncertain . "
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    ABSTRACT: Shiftwork, regarded as a significant occupational stressor, has become increasingly prevalent across a wide range of occupations. The adverse health outcomes associated with shiftwork are well documented. Shiftwork is an integral part of law enforcement, a high-stress occupation with elevated risks of chronic disease and mortality. Sickness absence is an important source of productivity loss and may also serve as an indirect measure of workers' morbidity. Prior studies of shiftwork and sickness absenteeism have yielded varying results and the association has not been examined specifically among police officers. The objective of this study was to compare the incidence rate of sick leave (any, ≥3 consecutive days) among day-, afternoon-, and night-shift workers in a cohort of police officers and also examine the role of lifestyle factors as potential moderators of the association. Participants (N = 464) from the Buffalo Cardio-Metabolic Occupational Police Stress (BCOPS) study examined between 2004 and 2009 were used. Daily work history records that included the shift schedule, number of hours worked, and occurrence of sick leave were available for up to 15 yrs starting in 1994 to the date of the BCOPS study examination for each officer. Poisson regression analysis for ungrouped data was used to estimate incidence rates (IRs) of sick leave by shift, and comparison of IRs across shifts were made by computing incidence rate ratios (IRRs) and their 95% confidence intervals (CIs). Sick leave occurred at a higher rate on the night shift (4.37 per 10 000 person-hours) compared with either day (1.55 per 10 000 person-hours) or afternoon (1.96 per 10 000 person-hours) shifts. The association between shiftwork and sickness absence depended on body mass index (BMI). For overweight individuals (BMI ≥ 25 kg/m(2)), the covariate-adjusted incidence rate of sick leave (≥1 day) was twice as large for night-shift officers compared with those working on the day (IRR = 2.29, 95% CI: 1.69-3.10) or afternoon (IRR = 1.74, 95% CI: 1.29-2.34) shift. The IR of three or more consecutive days of sick leave was 1.7 times larger for those working on night shift (IRR = 1.65, 95% CI: 1.17-2.31) and 1.5 times larger for those working on afternoon shift (IRR = 1.50, 95% CI: 1.08-2.08) compared with day shiftworkers. For subjects with normal BMI (<25 kg/m(2)), the incidence rates of sick leave did not differ significantly across shifts. In conclusion, shiftwork is independently associated with sickness absence, with officers who work the night shift having elevated incidence of sick leave. In addition, overweight officers who work the night shift may be at additional risk for sickness absence.
    Full-text · Article · Jun 2013 · Chronobiology International
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