Successive Night Shifts Research Articles

The acute effects of working time patterns on fatigue and sleep quality using daily measurements of 6195 observations among 223 shift workers.

Objectives:This study aimed to estimate acute effects of roster characteristics on fatigue and sleep quality and investigated whether these effects differed by individual characteristics.Methods:Using an ecological measurement assessment survey, fatigue and sleep quality were daily measured among 223 shift workers for up to eight weeks. A questionnaire assessed baseline characteristics, and roster data were retrieved from the company registers to determine roster parameters. The effects between each shift parameter on fatigue and sleep quality were estimated with random- and fixed-effects models.Results:Compared to day shifts, night shifts were related to fatigue [β=0.22; 95% confidence interval (CI) 0.05–0.39] and poorer sleep quality (β =0.64; 95% CI 0.47–0.80), and more successive night shifts with more fatigue (up to β=0.68; 95% CI 0.49–0.87 for ≥2 nights). Fatigue was increased after a quick return (<11 hours) (β=1.94; 95% CI 1.57–2.31) or 11–16 hours (β=0.43; 95% CI 0.26–0.61) compared to >16 hours between shifts. Compared to forward rotation, stable (β=0.22; 95% CI 0.01–0.43) and backward rotation (β=0.49; 95% CI 0.23–0.74) were also associated with more fatigue. Workers with a morning or intermediate chronotype had poorer sleep quality after a night shift, while workers with poor health reported poor sleep quality as well as more fatigue after a night shift.Conclusions:To alleviate acute effects of shift work on fatigue, shift schedules should be optimized by ensuring more time to recover and rotate forwards.

Time course of recovery after two successive night shifts: A diary study among Austrian nurses.

To explore how nurses recover from night shift work during periods off duty. Given the large number of affected individuals globally, detrimental health outcomes of night shift work are an important public health issue. Sufficient recovery opportunities are essential to prevent prolonged fatigue associated with demanding tasks and high workload as experienced in nurses working long shifts during the night. Nurses (n=53, 96% females) who worked in two public nursing homes in Austria completed a 5-day diary to collect data on well-being conceptualized by fatigue, distress and vigour. Nurses experienced worse well-being post night shift days than during rest days. Well-being improved from post night shift day 2 to the following rest day 1 and continued improvement from rest day 1 to rest day 2. Nurses who work at nights are at risk for experiencing prolonged fatigue. Our results suggest that after two consecutive 12-hr night shifts full recovery needs at least threedays off work. Strategies for maintaining nurses' good health and caring attitudes as well as vigilance for patient safety should include fatigue management plans and optimised schedules for night shift work.

The normalization of the cortisol awakening response and of the cortisol shift profile across consecutive night shifts—An experimental study

This study tested the hypothesis that the cortisol awakening response (CAR) and the cortisol shift profile normalize with successive night shifts due to the shift of the circadian system. 18 students (9 women, 9 men, 19-29 years), worked first four consecutive morning- and then four consecutive night shifts. Each work shift was preceded by an 8-h sleep opportunity meaning that the sleep-activity cycle was advanced by 8 h. The advance of the circadian system was promoted by a 2-h bright light pulse at the end of each night shift and quantified by 24-h phase assessment procedures (PA) before and after the four day shifts and again after the four night shifts. Saliva samples were taken 0, 15, 30, 45, and 60 min post-awakening, hourly during each work shift and each PA. During the night shift sequence, the CAR, indicated by the area under curve with respect to increase (AUC(I)), increased gradually across the 4-day sleep periods. Baseline levels were reached after 3 days in men and 4 days in women. The increase of the CAR was associated with a gradually increasing decline of cortisol levels during the night shifts. This adjustment was--at least not only--related to the advance of the circadian system which was 5 h. A contributor to the increase of the CAR might be the anticipation of the upcoming demands of the following work shifts.

Characterizing Recovery of Sleep after Four Successive Night Shifts

The purpose of this study was to characterize the recovery pattern of sleep following simulated, four successive night shifts in ten healthy men (22.9 + or - 3.2 yr). Poor sleep was defined as sleep efficiency of 80% or lower as determined actigraphically. The results showed that four (rapid, slow, pseudo, and incomplete) patterns of sleep recovery were observed over three recovery sleep periods. The rapid and slow recovery pattern represented immediate and slow return to baseline level prior to the nightshifts, respectively. The pseudo recovery pattern demonstrated poor sleep at the 3rd recovery sleep period, despite transient recovery at the 2nd sleep period. The incomplete recovery pattern was characterized by consistently poorer sleep during the entire recovery period. The correlation analysis indicated that sleep habits (bed time and variation of wake time) prior to the experiment were significantly related to the recovery patterns, rather than performance and alertness during the night shifts.

Laparoscopic Skills Suffer on The First Shift of Sequential Night Shifts: Program Directors Beware and Residents Prepare

Research evaluating fatigue-induced skills decline has focused on acute sleep deprivation rather than the effects of circadian desynchronization associated with multiple shifts. As a result, the number of consecutive night shifts that residents can safely be on duty without detrimental effects to their technical skills remains unknown. A prospective observational cohort study was conducted to assess the impact of 7 successive night shifts on the technical surgical performance of junior residents. The interventional strategy included training 21 residents from surgery and allied disciplines on a virtual reality surgical simulator, towards the achievement of preset benchmark scores, followed by 294 technical skills assessments conducted over 1764 manpower night shift hours. Primary outcomes comprised serial technical skills assessments on 2 tasks of a virtual reality surgical simulator. Secondary outcomes included assessments of introspective fatigue, duration of sleep, and prospective recordings of activity (number of "calls" received, steps walked, and patients evaluated). Maximal deterioration in performance was observed following the first night shift. Residents took significantly longer to complete the first (P = 0.002) and second tasks (P = 0.005) compared with baseline. They also committed significantly greater numbers of errors (P = 0.025) on the first task assessed. Improved performance was observed across subsequent shifts towards baseline levels. Newly acquired technical surgical skills deteriorate maximally after the first night shift, emphasizing the importance of adequate preparation for night rotas. Performance improvements across successive shifts may be due to ongoing learning or adaptation to chronic fatigue. Further research should focus on assessments of both technical procedural skills and cognitive abilities to determine the rotas that best minimize errors and maximize patient safety.

Shift Work, Safety, and Aging

It has long been recognized that older shift workers may have shorter and more disturbed day sleeps between successive night shifts than their younger colleagues. This has given rise to considerable concern over the safety of aging shift workers because of the increasing age of the work force and increases in retirement age. Because there have been no direct studies of the combined effects of shift work and age on safety, the present paper begins by reviewing the literature relating safety to features of shift systems. It then considers the general effect of age on occupational injury rates before examining existing evidence of the combined effects of shift work and age on performance capabilities. The results of the literature review indicate that when the a priori risk is constant, there is reasonably clear evidence that injury rates are higher at night, and that they increase over successive night shifts more rapidly than over successive day shifts. Further, although occupational injuries are less frequent in older workers, those that do occur tend to be more serious. Finally, there is some suggestive evidence from studies of objectively measured performance capabilities that older workers may be less able to both maintain their performance over the course of a night shift and cope with longer spans of successive night shifts. It is concluded that it seems possible, even though unproven as yet, that older workers may be at greater risk both to injury and accident on the night shift. There is a strong need for future epidemiological studies of the combined effects of shift work and age on injuries and accidents, and that these should attempt to separate the effects of age per se from those of generation.

Do Permanent Night Workers Show Circadian Adjustment? A Review Based on the Endogenous Melatonin Rhythm

“Permanent” or “fixed” night shifts have been argued to offer a potential benefit over rotating shift systems in that they may serve to maximize circadian adjustment and hence minimize the various health and safety problems associated with night work. For this reason, some authors have argued in favor of permanent shift systems, but their arguments assume at least a substantial, if not complete, adjustment of the circadian clock. They have emphasized the finding that the day sleeps taken between successive night shifts by permanent night workers are rather longer than those of either slowly or rapidly rotating shift workers, but this could simply reflect increased pressure for sleep. The present paper reviews the literature on the adjustment to permanent night work of the circadian rhythm in the secretion of melatonin, which is generally considered to be the best known indicator of the state of the endogenous circadian body clock. Studies of workers in “abnormal” environments, such as oil rigs and remote mining operations, were excluded, as the nature of these unique settings might serve to assist adjustment. The results of the six studies included indicate that only a very small minority (<3%) of permanent night workers evidence “complete” adjustment of their endogenous melatonin rhythm to night work, less than one in four permanent night workers evidence sufficiently “substantial” adjustment to derive any benefit from it, there is no difference between studies conducted in normal or dim lighting, and there is no evidence of gender difference in the adjustment to permanent night work. It is concluded that in normal environments, permanent night‐shift systems are unlikely to result in sufficient circadian adjustment in most individuals to benefit health and safety.

The suitability of a caffeinated energy drink for night-shift workers

Past research has indicated that caffeinated ‘functional energy drinks’ (FEDs) are effective in counteracting sleepiness. It is not known however, what impact FEDs have on sleep itself. FEDs contain several active ingredients, including caffeine. They may therefore impact negatively on sleep and hence subsequent performance, deeming their use counterproductive. In a randomised cross-over design, 15 young adults participated in a simulated first night-shift protocol with 2 conditions, Functional Energy Drink (FED) and Non Functional Energy Drink (NonFED). Both involved a period of extended wakefulness (0700–0730 h—24.5 h) followed by an 8-h daytime ‘recovery’ sleep (0730–1530 h). During the FED condition, a commercially available FED was administered twice during the night. Sleepiness was assessed during the period of extended wakefulness and for a further 6 h after waking. Sleep periods were recorded using a standard 5 channel polysomnogram. Comparison of the sleep periods showed that sleep onset latency remained unchanged as did stage 2 and slow wave sleep. Total sleep time however, was 29.1 min shorter ( p < .05) in the FED condition. Sleep efficiency was also significantly reduced from 91.8 ± .9% to 84.7 ± 2.7% ( p < .05). It is evident that the residual effects of the FED's active ingredients impact on some aspects of daytime sleep following a simulated night-shift. Subsequent performance however was unaffected. The results deem FEDs to be effective for a single night-shift and warrant investigation into their use over successive night-shifts.

Self-Reported Health and Sleep Complaints Among Nursing Personnel Working Under 12 h Night and Day Shifts

This cross-sectional exploratory study involved health care workers of various skill types and levels. We tested the hypothesis that the prevalence of diseases, sleep complaints, and insufficient time for nonprofessional activities (family, leisure, and rest) are higher among night than day workers. Data collection was carried out in two public hospitals using questionnaires and other forms. Night work was explored as a risk factor, considering a night worker as one who had at least one night job on the occasion of the research. Data were assessed by a univariate analysis. The association between work schedule and the dependent variables—health conditions, sleep complaints, and insufficient time for nonprofessional activities—was evaluated through the estimation of the prevalence ratio, with a confidence interval of 95%. Two hundred and fifty-eight female nursing personnel participated; 41.5% were moonlighters, and only 20 worked a shift of less than 12 h in length. Reports of migraine and need of medical care the 2 weeks before the survey were more prevalent among day than night workers (PR = 0.71; CI = 0.55–0.92 and PR = 0.71; CI = 0.52–0.95, respectively). Migraine headaches occurred less frequently among night than day workers as confirmed by comparing the reports of the night workers and day workers whose work history was always day shifts (PR = 0.74; CI = 0.57–0.96). Reports of mild emotional disorders (mild depression, tension, anxiety, or insomnia) were less frequent among night (PR = 0.76; CI = 0.59–0.98) and ex-night workers (PR = 0.68; CI = 0.50–0.91) than day workers who never had worked a night job. The healthy worker effect does not seem to explain the results of the comparisons between day and night workers. The possible role of exposure by day workers to some risk factors, such as stress, was suggested as an explanation for these results. No significant difference was observed between night and day workers as to sleep complaints, a result that may have been influenced by the nature of the shift-work schedule (no successive night shifts) and possibly nap taking during the night shift. Moreover, the long work hours and moonlighting of the healthcare workers, which is common in Brazil, may have masked other possible differences between the day and night workers. Among night workers, a significant relation was found between years working nights (more than 10 yrs) and high cholesterol values (PR = 2.58; CI = 1.07–6.27), a result that deserves additional study. Working nights more than four times per 2-week span was related to complaints about insufficient time for children (PR = 1.96; CI = 1.38–2.78) and rest/leisure (PR = 1.54; CI = 1.20–1.99). These results can be related to the “social value of time,” as evenings and nights are when families usually spend time together. The complexity of the professional life and the consequent heterogeneity of the group of workers under shift-work schemes confound the results. More in-depth study of the questions raised here demands a more sophisticated epidemiological treatment and larger sample size.

Shift work, safety and productivity.

The arguments in favour of introducing shift work clearly depend on productivity and safety being maintained at an acceptable level. However, the evidence reviewed in this paper clearly indicates that both productivity and safety may be compromised at night. More specifically, safety declines over successive night shifts, with increasing hours on duty and between successive rest breaks. The only known way to minimize these problems is to improve shift systems with respect to these factors. However, these factors need to be considered in combination with one another since, for example, a long night shift that includes frequent rest breaks might well prove safer than a shorter night shift with less frequent breaks.

The Use of Actimetry to Assess Changes to the Rest–Activity Cycle

The endogenous circadian oscillator (the body clock) is slow to adjust to altered rest–activity patterns. As a result, several negative consequences arise during night work and after time‐zone transitions. The process of adjustment can be assessed by measurements of the sleep electroencephalogram (EEG), core temperature or melatonin secretion, for example, but these techniques are very difficult to apply in field studies, and make very great demands upon both experimenters and subjects. We have sought to establish if the activity record, measured conveniently and unobtrusively by a monitor attached to the wrist, can be treated in ways that enable estimates to be made of the disruption caused by changes to the rest–activity cycle, and the process of adjustment to them. In Part A, we describe the calculation and assessment of a series of “activity indices” that measure the overall activity pattern, activity when out of bed or in bed, or the activity in the hours adjacent to going to bed or getting up. The value of the indices was assessed by measuring changes to them in subjects undergoing night work or undergoing time‐zone transitions. In both cases, there is a large body of literature describing the changes that would be expected. First, night workers (working 2 to 4 successive night shifts) were investigated during rest days and night shifts. The indices indicated that night work was associated with lower activity when the subjects were out of bed and higher activity when in bed. Some indices also measured when subjects took an afternoon nap before starting a series of night shifts and gave information about the process of adjustment to night work and recovery from it. Second, in studies from travelers crossing six or more time zones to the east or west, the indices indicated that there were changes to the rest–activity cycle immediately after the flights, both in its overall profile and when activity of the subjects in bed or out of bed was considered, and that adjustment took place on subsequent days. By focusing on those indices describing the activity records during the last hour in bed (LHIB) and the first hour out of bed (FHOB), some evidence was found for incomplete adjustment of the body clock, and for differences between westward and eastward flights. In Part B, the battery of indices are applied to the activity records of long‐haul pilots, whose activity patterns showed a mixture of effects due to night work and time‐zone transitions. Actimetry was performed during the flights themselves and during the layover days (which were either rest or work days). The indices indicated that all pilots had disrupted rest–activity cycles caused by night flights, and that there were added problems for those who had also undergone time‐zone transitions. Rest days were valuable for normalizing the activity profile. For those pilots who flew to the west, adjustment was by delay, though not all aspects of the rest–activity cycle adjusted immediately; for those who flew to the east, some attempted to advance their rest–activity cycle while others maintained home‐based activity profiles. The indices indicated that the activity profile was disrupted more in those pilots who attempted to advance their rest–activity cycle. We conclude that objective estimates of the disruption caused to the rest–activity cycle and the circadian system can be obtained by suitable analysis of the activity record.

Beyond the three-process model of alertness: estimating phase, time on shift, and successive night effects.

This paper starts by summarizing the development and refinement of the additive three-process model of alertness first published by Folkard and Akerstedt in 1987. It reviews some of the successes that have been achieved by the model in not only predicting variations in subjective alertness on abnormal sleep-wake schedules but also in accounting for objective measures of sleep latency and duration. Nevertheless, predictions derived from the model concerning alertness on different shifts, and over successive night shifts, are difficult to reconcile with published data on accident risk. In light of this, we have examined two large sets of alertness ratings with a view to further refining the model and identifying additional factors that may influence alertness at any given point in time. Our results indicate that, at least for the range of sleep durations and wake-up times commonly found on rotating shift systems, we may assume the phase of the endogenous circadian component of alertness (process C) to be "set" by the time of waking. Such an assumption considerably enhanced the predictive power of the model and yielded remarkably similar phase estimates to those obtained by maximizing the post-hoc fit of the model. We then examined the manner in which obtained ratings differed from predicted values over a complete 8-day cycle of two, 12-h shift systems. This revealed a pronounced "first night compensation effect" that resulted in shift workers rating themselves as progressively more alert than would be predicted over the course of the first night shift. However, this appeared to be achieved only at the cost of lowered ratings on the second night shift. Finally, we were able to identify a "time on shift" effect whereby, with the exception of the first night shift, alertness ratings decreased over the course of each shift before showing a modest "end effect." We conclude that the identification of these additional components offers the possibility that in the future we may be able to predict trends in accident risk on abnormal sleep-wake schedules.

Ageing, physical fitness and shiftwork tolerance

The effects of ageing and physical fitness on shiftwork tolerance are reviewed. Ageing is one of the most cited factors decreasing the health of shiftworkers. Although long-term prospective studies on ageing are few, shiftworkers over 40–45 years of age seem to sleep worse after night, but not after morning shifts. Sleepiness after successive night shifts is also decreased by age although older shiftworkers' ability to resist acute sleep loss seems to be even better. The reasons for the altered sleep and wakefulness of older shiftworkers are probably related to changes in circadian rhythms, especially higher ‘morningness’. Sleep need may also decrease with age which could explain some of the differences found in sleep length. Physical fitness as a factor increasing tolerance to shiftwork is a recent finding. Although the effects of physical activity on sleep have been studied in detail, the relationship of physical fitness to sleep is still a controversial issue. In shiftworkers, moderate physical training has been shown to increase sleep length and night-time alertness. It has not been shown, however, that exercise would quicken the circadian adjustment to night work. It is recommended that work time arrangements should take account of the older workers' changing personal references. Continuous night work should be voluntary after 40 years of age. Moderate physical exercise a few hours before the main sleep period is recommended.

Separating the endogenous and exogenous components of the circadian rhythm of body temperature during night work using some 'purification' models.

Ten nurses have been studied for a period of about ten days during which they had rest days and between two and seven successive night shifts. Rectal temperature and wrist movement were monitored throughout, and the nurses kept an activity log. The process of adjustment to night work was assessed by comparing shifts in body temperature with those in mid-sleep, using the mean of the values during rest days as a control in both cases. When raw temperature data were used, the measured shifts were significantly greater than when the temperature data were first modified or 'purified' by a series of methods that took into account the direct effects upon temperature of sleep and physical activity. The greater the 'purification' of the data--whether by using an activity profile derived from a wrist accelerometer or the subject's own log--the less rapid did adjustment to night work appear to be. We conclude that conventional measurements of the adjustment of the temperature rhythm to night work that make use of raw data over-estimate it due to masking effects. We suggest also that the purification methods that we have developed can be used in the field and enable estimates to be made of the size of masking effects caused by sleep and activity, as well as the shift of the endogenous component of the circadian rhythm.

Productivity on a weekly rotating shift system: circadian adjustment and sleep deprivation effects?

Abstract There is little doubt that productivity and safety can be impaired on the night shift. Two main factors have been identified that may be responsible for this. On the one hand, the circadian rhythm in performance on at least simple tasks is at a low ebb at night, and adjusts only slowly over a span of night shifts. On the other, the day sleeps of shift workers taken between night shifts are of a reduced duration, and thus a cumulative sleep debt may accrue over successive night shifts. The former thus predicts that productivity should improve over a span of night duty, while the latter predicts that it should decline. We have examined the productivity of 53 female shift workers, and the sleeping habits of a sub-sample of 30 of them, on a weekly rotating shift system in order to assess the relative contribution of these two factors. Our results suggest that circadian adjustment to night work is the dominant factor for the first three or four successive nights shifts, but that sleep deprivation effe...

Effects of consecutive night-shift work on health conditions among car-cleaners of super-express trains.

The Shinkansen Super-Express trains of the Japanese National Railways, the so-called bullet trains, run from early morning until late at night. Accordingly the car-cleaners of the Shinkansen must do late night shift work. A self-administered questionnaire survey including items about health and work conditions was given to 246 workers at Osaka Station, who were then divided into 3 groups: Group A consisted of 102 night workers working 5 successive days with 2 days off, Group B consisted of 124 alternate-day 24-hour workers working 3 days a week, while Group C included 20 day-workers working 6 days a week. A subjective fatigue inventory was administered before and after work for a week to 20 workers selected from each of three groups, group A, B above group D whose shift was 2 times 2 successive night shifts with one day off, and one holiday a week. The results of the questionnaire survey revealed that the rates of complaints such as gastroenteric disorders and general fatigue were the highest in group A. The results of the subjective fatigue inventory show a tendency for the number of complaints in group A and B to increase significantly after the last work shift of the week, but not in the case of group D. The authors demonstrated that there was a close relationship between patterns of night-shift work and various kinds of health problems, and concluded that to insert a day off on the third day of the group D shift was effective in reducing the work load.

Physiological limits of locomotive drivers on successive night shifts in the People's Republic of China.

Physiological limits of locomotive drivers on successive night shifts in the People's Republic of China.

A study of weekly and rapidly rotating shiftworkers

Diary sleep and oral body temperature data are presented for two groups of experienced rotating shiftworkers (2 or 3, and 5 successive night shifts).

Re-entrainment of body temperature in experimental shift-work studies.

In a series of experimental shift work studies six subjects worked on continuous night shift for three weeks, four subjects worked on a 1-1-1 shift system (1st day morning shift, 2nd day afternoon shift, 3rd day night shift, 4th day off), and two subjects worked on an 2-2-2 shift system (the ‘metropolitan rota’). Rectal temperature was continuously recorded in each experiment. The greatest changes in the circadian rhythm of body temperature occurred on the second night shift day, and during the first week of continuous night shift working. The changes involved both shifts in the phasing of the rhythm, and alterations in its form. The re-entrainment of the rhythm to its normal phasing took two or more days after two or more successive night shifts, but only one day after a single night shift. Considerable individual differences in the rhythm adjustment to night work were observed. In a field validation of these findings, 34 shiftworkers in municipal gas and water supply undertakings measured their oral tem...

Short and long-term adjustment of circadian rhythms in 'permanent' night nurses.

Two studies are described in which differences were found in the adjustment of the circadian rhythms of full and part-time night nurses to night work. A distinction was drawn between short-term adjustment that takes place over successive night shifts, and long-term adjustment that may take the form either of a permanent ‘flattening’ of the rhythm, or of a facilitation of short-term adjustment. The results from the first study indicated that even when the potential for greater short-term adjustment was controlled for, the full-time staff showed greater adjustment to night work. The second study examined these differences in long-term adjustment in greater detail. No evidence was found of a permanent ‘flattening’ of the full-timers’ circadian rhythms, although they showed clear evidence of adjustment even on the first of a period of successive night shifts. The full-timers also showed more evidence of adjustment from the first to the second night shift. It is suggested that these differences in long-term ad...