Tolerance to shift work—how does it relate to sleep and wakefulness?

Objectives There is limited knowledge as to why some individuals tolerate shift work and others do not. As a consequence of their intolerance, many individuals develop dissatisfaction with their shift schedule. To evaluate if dissatisfaction with ones shift system was related to alterations of the daily pattern of sleep and sleepiness, we followed two groups of shift workers that were either highly satisfied or dissatisfied with their shift schedule, during an entire shift cycle.Methods Thirty-six male and 20 female shift workers were selected according to their satisfaction with their shift schedule. The shift cycle included seven work periods (triads of shifts; night shift—afternoon shift—morning shift), with only 8–9 hours off (quick returns) between shifts, but followed by a day off.Results Sleep length was reduced after night shifts (4.8 h) and afternoon shifts (5.4 h). Sleepiness was increased during all shifts, particularly night shifts. Sleepiness did not accumulate across the shift cycle even though sleepiness was slightly increased directly after the last triad of shifts. There were few significant gender differences. Dissatisfied shift workers reached much higher levels of sleepiness and reported less sufficient sleep, but not objectively poorer or shorter sleep. Amongst dissatisfied workers, this resulted in an increase of sleepiness problems across shifts within the triad of shifts. Dissatisfied workers also had more performance lapses at the end of the night shift.Conclusions Satisfaction with the shift schedule seems to reflect how well the shift workers were coping with the schedule. It is suggested that the increase of sleep/wake problems within the work period for the dissatisfied shift workers is related to increased sensitivity to curtailed and displaced sleep.     

Spectral analysis of sleep electroencephalography in rotating three-shift work

Fourteen male rotating three-shift workers were subjected to 24-h ambulatory polysomnographic recording in connection with morning, afternoon, and night shift work (at home and at work). Total sleep time, stage 2, rapid-eye-movement sleep, and slow-wave sleep (stages 3 + 4) were significantly reduced during sleep in connection with the night and morning shifts. Other visually scored sleep parameters and slow-wave energy (spectral power density integrated across sleep) were not affected. The content of the sleep cycles did not differ between shifts. The sleep before the morning shift was characterized by subjectively increased difficulties of sleep initiation and sleep termination, as well as by insufficient recuperation. The night shift was characterized by increased subjective difficulties of maintaining sleep, but also by increased ease of sleep initiation. It was concluded that both morning and evening shifts interfered with sleep, although no effects of sleep deprivation were found.     

Experimental shift work studies of permanent night,and rapidly rotating,shift systems

Summary In connection with experimental shift work 20 volunteers were examined while working on different rapidly or slowly rotating shift systems. Sleep was analysed over a total of 112 days.Sleep was disturbed by childrens' noise or traffic noise. Sleep duration and sleep quality were particularly badly affected by noise with a high information value (childrens' noise).The ultradian rhythmicity of sleep did not appear to be disrupted by the change from day to night work.There were no significant differences between morning sleep and afternoon sleep after night work.In the laboratory experiments with fixed sleep durations, no separate effects on sleep quality could be established for different shift systems.     

Characteristics of main and additional sleep time in workers on rotating shifts

Various sleep characteristics were examined among rotating shift workers (n = 603) and control workers (n = 113). The results showed the shift workers to have poorer sleep quality than the control group. In addition their main sleep episode was shorter on morning shift and longer on days off in comparison to controls. Shift workers' main sleep length and frequency of napping were affected by the situation in which they were taken (morning, afternoon, night shift or days off). In the group of shift workers the short main sleep episode on morning and night shifts was compensated by longer sleep on afternoon shift and days off. The short night shift sleep was additionally compensated by napping. However, naps taken on the morning shift did not prove to be compensatory. The length of the main sleep episode was affected by the situation in which sleep was taken also in the control group of workers. In this group only the longer main sleep episode on days off appeared to have a compensatory function for the short main sleep on working days. The relationship between sleep quality and main sleep duration was determined by the situation in which sleep was taken, while the relationship between sleep quality and napping was established only for the control group of workers.     

Quantitative and qualitative aspects of sleep in young self-selected four-shift workers

Summary For 4 of 5 weeks, 27 shift workers daily registered the times they went to sleep and awoke and sleep difficulties. The subjects are employed in a semi-continuous four-shift system. A complete cycle comprises: six morning, six afternoon, and six night shifts, and six free days. Sunday is always free.The mean duration of sleep per 24 h over the 4 weeks is 8 h. The amount of sleep is significantly larger during the free week (8 h 18 min) and significantly smaller during the night shift week (7 h 26 min), when compared to the amounts of sleep in each of the other 3 weeks. Difficulties in getting to sleep and sleep interruptions are more common during day-sleep in the nightshift. Subtracting some time for every sleep interruption does not noticeably change the sleep duration data yielded for the night shift.These results suggest that the duration and quality of sleep of these shiftworkers living in a rural region is quite satisfactory. This can perhaps be explained by the time schedules used in this shift system, by compensation for relative lack of sleep made possible by the free week, by some (self-)selection of the workers, and finally by their young age.     

Meals, snacks and food choices in Brazilian shift workers with high energy expenditure

Objective To describe the food intake of garbage collectors, who works in three shifts, in terms of meal and snack frequency, content, time distribution and the contribution of various popular foods to the total diet. Methods Sixty‐six Brazilian garbage collectors, who work in morning, afternoon, and night shift, participated in the present study. The quantitative methods used were a combination of one 24‐h recall and two 24‐h records during three nonconsecutive work days. The qualitative method used was the food‐based classification of eating episodes model modified in order to define meals or snacks in three categories of events: meals with three food groups of high nutrient density (three HND meals), meals with two food groups of high nutrient density (two HND meals) and snacks, composed of only one food category of high nutrient density. Results The total number of eating events per day was significantly higher for night shift workers. Over 24‐h, ‘two HND meals’ were the most common events and contributed the most energy, in all three shifts. Night shift workers ate more at dawn and less in the morning than other shifts. In all three shifts, meat was the most important food contributing to energy intake. Conclusion Different work schedules did not affect the relative frequency of meal types and snacks or their contribution to daily energy intake, but affected the daily distribution of eating events, with a redistribution of intake from day to night in night shift workers.     

Effects of diurnal and seasonal sleep deficiency on work effort and fatigue of shift workers

Summary This study was designed to assess and compare the quantity and quality of sleep of morning, afternoon, and night shift workers during the winter and summer seasons, and to evaluate the effects of sleep deficiency on the work effort and fatigue of the workers. The subjects studied consisted of a sample of 150 textile workers, working on a monthly rotating 3-shift system: morning shift (06.00–11.00 and 14.00–17.00) afternoon shift (11.00–14.00 and 17.00–22.00), and night shift (22.00–06.00). Information concerning quantity and quality of sleep were registered daily over a week for every subject. The Ratings of Perceived Effort scale and the Feeling and Symptoms of Fatigue scale were used to collect information about feeling of effort and fatigue of the subjects. The results showed that the duration of sleep length is longest in the afternoon and shortest in the night shift both during summer and winter. The amount of sleep is shorter during summer during all three shifts. The workers spent more effort and felt more fatigued during summer than winter. The shift workers, particularly of the tropical region, like Bangladesh, seem to be worst affected in terms of quantity and quality of sleep, health and well-being due to extremely high temperature (30–45° Celsius) during summer than winter (5–25° Celsius). The workers think that the problems of shift work could be minimized by improving the quality of working and living conditions, reducing cycle of rotation, shortening working day and closing night shift during peak summer.     

A study of weekly and rapidly rotating shiftworkers

Summary Diary sleep and oral body temperature data are presented for two groups of experienced rotating shiftworkers (2 or 3, and 5 successive night shifts).The data analysis shows for both rotas: a flattened temperature curve on night shift; sleep loss on both morning and night shift; few breaks in sleep for either day or night sleeps, with no significant increase for day sleeps; a marked tendency for no-day sleep to be taken prior to the first night shift; and a shorter latency to sleep onset for day sleep.The night shift body temperature curves and diary sleep data are related to earlier studies. They are interpreted as reflecting partial—not chronic—sleep loss, and an ongoing normal circadian rhythmicity.No particular number of consecutive night shifts is recommended. Rather it is suggested that shift rota selection should be based on an assessment of how the rota will facilitate an acceptable balance between useful free time and sleep duration for individual work groups.     

Elevated salivary cortisol levels as a result of sleep deprivation in a shift worker

BACKGROUND: This paper reports a case from a group of 63 shift-workers for whom adaptation to shift-work was evaluated through measurement of salivary cortisol levels. METHODS: Workers' saliva was sampled and cortisol levels measured at intervals of 2 h during morning, evening and night shifts. RESULTS: For one subject among the 63, very high values of cortisol (an approximately 6-fold increase) were observed for the morning (M) shift, but with normal values found for evening (E) and night (N) shifts. Individual mean and peak cortisol values were 48.4 and 67.8 nmol/l against group mean and peak cortisol values of 8.9 and 11.0 nmol/l. Retrospective questioning showed that this subject was healthy and there were no indicators of long-term stress. CONCLUSION: This cortisol rise was deduced to be caused by sleep deprivation as a result of rapidly rotating shift patterns.     

The effects of the number of consecutive night shifts on sleep duration and quality

Objectives:The organization of night shift work affects sleep duration and quality. The aim of this study was to investigate the effects of the number of consecutive night shifts on sleep duration and quality among police officers with night shift work as part of their normal schedule.Methods:This quasi-experimental, within-subject crossover study included 73 police officers. All participants performed three work schedules: two, four and seven consecutive night shifts followed by the same number of recovery days, ie, day work or days off (2+2, 4+4, and 7+7). Sleep assessed through sleep diaries and actigraphy after all night shifts and recovery days (totaling 26 days) was compared by use of repeated measures analysis.Results:Participants experienced shorter sleep duration (with and without naps), more premature awakening, less difficulty falling asleep, and more non-refreshing sleep after night shifts compared with recovery days. Sleep duration and quality did not change with increasing number of consecutive night shifts. Sleep was shorter and of poorer quality after the last night shift in the 2+2 and 4+4 work schedule compared with the second and fourth night shift, respectively, in the 7+7 schedule.Conclusion:Sleep duration was reduced after night shift work and did not increase with more consecutive night shifts, which leads to accumulated sleep debt. Sleep duration was shortest and sleep quality was poorest after the last night shift in a series of night shifts.