Permanent Night Shift Research Articles

P1086 常夜勤務に従事する女性労働者の生活実態と健康影響の評価手法の検討(第1報)(一般演題:ポスター,地方の時代の産業保健,第79回日本産業衛生学会)

P1086 常夜勤務に従事する女性労働者の生活実態と健康影響の評価手法の検討(第1報)(一般演題:ポスター,地方の時代の産業保健,第79回日本産業衛生学会)

A Compromise Phase Position for Permanent Night Shift Workers: Circadian Phase after Two Night Shifts with Scheduled Sleep and Light/Dark Exposure

Night shift work is associated with a myriad of health and safety risks. Phase‐shifting the circadian clock such that it is more aligned with night work and day sleep is one way to attenuate these risks. However, workers will not be satisfied with complete adaptation to night work if it leaves them misaligned during days off. Therefore, the goal of this set of studies is to produce a compromise phase position in which individuals working night shifts delay their circadian clocks to a position that is more compatible with nighttime work and daytime sleep yet is not incompatible with late nighttime sleep on days off. This is the first in the set of studies describing the magnitude of circadian phase delays that occurs on progressively later days within a series of night shifts interspersed with days off. The series will be ended on various days in order to take a “snapshot” of circadian phase. In this set of studies, subjects sleep from 23:00 to 7:00 h for three weeks. Following this baseline period, there is a series of night shifts (23:00 to 07:00 h) and days off. Experimental subjects receive five 15 min intermittent bright light pulses (∼3500 lux; ∼1100 µW/cm2) once per hour during the night shifts, wear sunglasses that attenuate all visible wavelengths—especially short wavelengths (“blue‐blockers”)—while traveling home after the shifts, and sleep in the dark (08:30–15:30 h) after each night shift. Control subjects remain in typical dim room light (<50 lux) throughout the night shift, wear sunglasses that do not attenuate as much light, and sleep whenever they want after the night shifts. Circadian phase is determined from the circadian rhythm of melatonin collected during a dim light phase assessment at the beginning and end of each study. The sleepiest time of day, approximated by the body temperature minimum (Tmin), is estimated by adding 7 h to the dim light melatonin onset. In this first study, circadian phase was measured after two night shifts and day sleep periods. The Tmin of the experimental subjects (n=11) was 04:24±0.8 h (mean±SD) at baseline and 7:36±1.4 h after the night shifts. Thus, after two night shifts, the Tmin had not yet delayed into the daytime sleep period, which began at 08:30 h. The Tmin of the control subjects (n=12) was 04:00±1.2 h at baseline and drifted to 4:36±1.4 h after the night shifts. Thus, two night shifts with a practical pattern of intermittent bright light, the wearing of sunglasses on the way home from night shifts, and a regular sleep period early in the daytime, phase delayed the circadian clock toward the desired compromise phase position for permanent night shift workers. Additional night shifts with bright light pulses and daytime sleep in the dark are expected to displace the sleepiest time of day into the daytime sleep period, improving both nighttime alertness and daytime sleep but not precluding adequate sleep on days off.

Effects of working permanent night shifts and two shifts on cognitive and psychomotor performance

The study aimed to clarify whether cognitive and psychomotor performance, which are important for occupational and traffic safety, are impaired by working permanent night shifts (NSs) compared with early-late two shifts (TSs) and whether age and chronobiological type influences the relationship between shift and performance. The study included 44 male automobile workers, 20 working TSs and 24 working NSs. Chronobiological type was determined by questionnaire (D-MEQ). Each subject was tested at the beginning and end of the shift for alertness [by a visual analogue scale (VAS)]; feeling of well-being (Basler); concentration and accuracy (d2); reaction speed, orientation and reaction to stress (Vienna System). TS workers were more frequently morning types whereas the NS workers were more frequently evening types. In the performance tests, the TS and NS workers did not differ at shift start or shift end. Over the course of the shift, concentration and accuracy improved in both groups, as did reaction to stress. Chronobiological type alone or in combination with shift type had no effect on performance. The results of this study indicate that-if chosen voluntarily-working NSs has no immediate negative effects on cognitive and psychomotor performance when compared with working TSs. There was no indication of an increased risk of accidents after working NSs. The unequal distribution of the circadian types in the shift groups may indicate selection.

Do the work stress factors of women telephone operators change with the shift schedules?

The work stresses of women VDT-cum-telephone operators ( N=136), including the effects of permanent (day, evening and night) and rotating shifts on the behavioral responses and health disturbances were examined. The operators responded to an ergonomics checklist on work system analysis (e.g., job characteristics, physical and psychosocial stresses of work, workplace constraints, musculo-skeletal and visual strains, environmental hazards, and operator–VDT and telecommunication equipment interaction). The effects of shift schedules on health and well being were examined using questionnaires on sleep quality and quantity, physical health symptoms, chronic fatigue, cognitive and somatic anxiety, social and domestic disruption, composite morningness score, circadian type inventory (languidness and flexibility) and Eysenck personality inventory. The principal component factor analysis of the ergonomics checkpoints yielded five aspects of work. Factor 1 (organizational) describes job design needs, workplace interventions and constraints of VDT workstations. Factor 2 (environmental) covers illumination, climate and noise-related hazards. Factor 3 (mechanistic) refers to job specialization, pace of work, information handling, etc. Factor 4 (perceptual and motor) describes visual and auditory displays and controls. Factor 5 (motivational) refers to personal job characteristics and core dimensions, such as job autonomy, task significance and recognition. Factors 1–3 represented 45% of the total variance; Factors 4 and 5 represented 19% of the total variance. Long hours of seated work resulted in musculo-skeletal strains, however, the evening and night shift operators had highest back-related complaints (45–48%), compared to those in the day (28%) and rotating shifts (34%). The operators in the rotating and permanent night shifts had higher prevalence of visual strain. The loading of the work stressors explained in Factors 1–3 appeared autonomous, irrespective of the shift schedules. ANOVA and Tukey's HSD test indicated that the operators in the rotating shift had greater sensitivity to the stressors related to Factor 4. While the day shift operators responded greater to the stressors related to the core job dimensions that reflect growth needs (Factor 5), the night shift operators were less responsive to those dimensions. The scores on sleep disturbance, flexibility to sleeping habits and personality dimension (neuroticism) were negatively correlated to Factor 1. The digestive problems, social and domestic disruption and languidity dimensions were positively correlated to Factors 4 and 5. As noted in case of the rotating shift, the increased demand in the perceptual and motor, and the motivational aspects of work caused greater negative influence on physical health symptoms, and social and domestic disruption. The somatic anxiety was greater among women in night work. Findings of the multiple aspects of work supported that the behavioural response to the work stressors, and health and well-being dimensions did vary with the shift schedules. The job design interventions tailoring to the type of work and workplace ergonomics might improve the work stressors. The overlapping schedules of the rotating shift, including night work are the documented risk factors. Delayed morning shift for the operators in the rotating shift and adjustment of shift length based on the work and climatic load (e.g., reduce work hours in the evening shift to avoid peak workload, extend work hours in the day shift during the extremely hot summer months) might alleviate work stresses and enhance health and well-being. Relevance to industry Macroergonomic analysis of work in the telecommunication sector elucidates the multiple aspects of work stressors, including the shift schedules. In the light of cumulative health effects of the women VDT-cum-telephone operators, the study explores intervention and management of work to alleviate work stresses and enhance health and well being of the people involved.

Analysis of the relationship between nurse influences over flexible working and commitment to nursing.

The paper explores the theoretical and practical bases of both commitment and control within the context of temporal aspects of flexible working in nursing. The aims of the paper are to examine the relationships between nurses' shift patterns, influence over shift pattern and realization of shift preference and commitment to nursing. Data were collected through a postal questionnaire completed by 2987 British nurses employed in hospitals, care homes and hospices. Principal components analysis was used to identify common factors among responses to a series of 33 statements about working life. Data were analysed using ANOVA and multiple regression techniques. Permanent night shift nurses reported lower levels of commitment to nursing. As predicted, influence over shift patterns and realization of preferred shift pattern were positively associated with commitment to nursing, although the relationship was weak. Positive perceptions of career development opportunities were a stronger predictor of commitment to nursing. Results are discussed in light of previous ethnographic research on nurses' shift patterns. The opportunity to explore quantitatively the effects of shift-related decisions on commitment using a large sample is useful. While influence and shift type were predictors of commitment, the positive impact they were expected to have was smaller than expected. Similarly, the negative effects of not having influence or of working permanent night shifts were smaller than expected and the statistical significance of such small effects relies heavily on the large sample obtained. Other variables, particularly career development prospects, outweigh the influence of shift-related variables on commitment. The research gives a clear message to human resource managers involved with nurse management: so long as nurses have a strong perception of career development potential the otherwise negative influences of shift impact can be minimized.

‘Doing Life’: Gender Relations in a Night Nursing Sub‐Culture

This paper explores a night nursing sub‐culture which is struggling to survive. The context is the NHS in the UK. This exclusively female group within an organization numerically dominated by women evokes hostile reactions from other cultural groups within the NHS, based on its perceived espousal of ‘female’ ways of being. Increasingly threatened by the new managerialism of the NHS, the permanent night shift faces extinction as a group. This paper describes the night nurse culture as it exists in a general hospital and offers some insights into the way that gender relations evolve to sustain male power in an organization where women are numerically dominant.

Differential Effects of Permanent and Rotating Shifts on Self-Report Sleep Length: A Meta-Analytic Review

The current study used the meta-analytic technique to quantitatively assess the effects of permanent and rotating shift-work schedules on sleep length. A meta-analysis was completed on 36 primary studies resulting in 165 effect sizes. Effect sizes comparing shift-workers to a permanent day shift control group were calculated for permanent evening shifts, permanent night shifts, and morning, evening, and night shifts worked as part of slowly and rapidly rotating shift systems. NA PATIENTS OR PARTICIPANTS: NA INTERVENTIONS: NA RESULTS: Permanent night shifts resulted in a decrease, whereas permanent evening shifts resulted in an increase in sleep length. The shifts within rotating schedules followed the same pattern, with the addition of morning shifts having a moderate detrimental effect on sleep length. Furthermore, the speed of shift rotation had an impact. Slowly rotating shifts, in general, had the least detrimental effect on sleep length of the permanent and rotating shift-work schedules studied here. The pattern of effects among morning, evening, and night shifts was the same for rapidly and slowly rotating shifts, with night shifts having the greatest detrimental effect, morning shifts having a moderate detrimental effect and evening shifts having a positive effect on sleep length. In addition, nights on rotating shifts had a greater negative effect on sleep length than permanent night shifts. Slowly rotating shifts have the least negative impact on sleep length of shift-work schedules including a night shift. However, permanent night shifts could be an alternative shift-work schedule in operational settings that require many workers at night.

Rapid Shift in Peak Melatonin Secretion Associated With Improved Performance in Short Shift Work Schedule

We studied the performance and adaptability of 40 nurses (median age 35 years), 20 on permanent day shift and 20 on permanent night shift with fast rotation of work and days off, matched for age, gender, and socio-familial responsibilities. For 15 days prior to the study, subjects maintained sleep logs and trained for performance tests. Questionnaires were administered to evaluate adaptability to shift work. During the experimental phase, sleep/wake patterns were monitored using sleep logs and activity/inactivity with wrist actigraphy. Performance levels were measured with the four choice reaction time and memory test for seven letters, eight times/day during the wake period, days on and off. On the last day of work and first day off, 6-sulfatoxy-melatonin levels were assayed from urine samples collected every 2 hours. Estimated total sleep time during the 15-day experimental period was not significantly different in the dayshift and nightshift nurses. Night nurses shifted regularly to daytime activities on days off and, as a group, were significantly sleep deprived on work days with napping on the job in 9 of the 20 night shift nurses (mean of 114+/-45 minutes per shift) and a significant performance decrement during the work period. Further analysis revealed two subgroups of night nurses: The majority (14 nurses) had a mean peak of 6-sulfatoxy-melatonin at 0718 hours on days off and no peak during night work while the other 6 night shift nurses presented a fast melatonin shift with two clear peaks on both work and days off. Comparison of performance scores revealed that all nurses performed similarly on days off. Daytime nurses and fast-shifting night nurses had similar scores on work days, while nonshifting night nurses had significantly lower scores at work. Despite similar gender, age, social conditions, and light exposure levels, a minority of the nurses studied possessed the physiological ability to adapt to a fast-shifting sleep-wake schedule of more than 8 hours and were able to perform appropriately in both conditions. This shift was associated with a change in the acrophase of 6-sulfatoxy-melatonin.

The lights are bright? Debating the future of the permanent night shift.

Debates a controversial issue in healthcare management, that is, whether internal rotation (day-night) or permanent night shifts is an appropriate shift system for nursing staff. A multidisciplinary approach draws together international research from the fields of occupational psychology, management, ergonomics and medicine. Explores evidence on sleep, physical and mental health, job satisfaction, performance, absenteeism, and social and domestic disruption, all important factors in considering appropriate shift patterns. Suggests that both nurse choice (or non-choice) of shift and adjustment, or otherwise, of circadian rhythms are important causal factors influencing the debate. As no unequivocal picture emerges, recognizes some of the real and potential limitations of a paper of this kind; however, the balance of argument tends to favour the maintenance of permanent night shift nurses as opposed to the further extension of internal rotation systems. This is especially the case as many nurses will still be given a choice of shift pattern which may, in itself, negate some of the potential ill-effects of night working. Decisions further to extend internal rotation may, in the light of the complex, ambiguous and equivocal evidence, be informed by partial knowledge and influenced by a managerial perspective.

Shiftwork and the older worker.

The number of workers employed on shiftwork is large, and it appears to be increasing. The impact of shiftwork on the occupational safety and health of workers is complex and involves both biological and behavioral variables. Current conceptual models propose that the impact of shiftwork, where night work is involved, increases with exposure. At some point the worker is said to reach a tolerance limit beyond which shiftwork is no longer safe. Sleep variables have proven to be sensitive markers for the effects of night shiftwork. Data from U.S. workers show a statistically significant interaction among age, gender, and shift for the workday sleep length of workers on permanent day, afternoon/evening, and night shifts. Sleep length declines with age for both male and female night workers, as well as for male workers on afternoon/evening shifts. In addition, female night workers in the 18-49 age range sleep significantly less than same-age male night workers. Nap behavior also varies with shift, but age and gender effects do not appear to account for the variance. The results support the assumption that most night shiftworkers are at risk even though they often give the appearance of being able to tolerate nocturnal work hours. However, it is not yet clear how age and gender are related to the social, circadian, and environmental factors that influence the sleep length of shiftworkers.

The circadian melatonin and cortisol secretion pattern in permanent night shift workers

In permanent night shift workers the impact of environmental time cues on the circadian system is conflicting. Rhythm adjustments to the nocturnal work schedule have been described, and their significance for tolerance to shift work is under discussion. Reports concerning the effect of this work situation on the setting of the endogenous clock are, however, inconsistent. We examined nine healthy young male permanent shift workers with high work satisfaction at the end of a week on night work and seven male controls with normal diurnal working hours. All subjects were admitted to a research facility for 28 h, and blood was collected with a continuous-withdrawal pump in portions taken hourly for the estimation of the circadian melatonin (MT) and cortisol secretion pattern. One control did not exhibit a circadian secretion pattern. When compared with the other controls (n = 6), all except one of the shift workers showed no difference in the phase or phase relationship of their hormonal profiles. In the shift workers, a minor trend toward elevation of the MT amplitude and an increase in two indicators for the amount of MT secreted were noticed. One individual displayed inverse hormone rhythms with an undisturbed phase relationship of MT and cortisol and inconspicuous hormone amplitudes. He showed, however, an inverse day-night rhythm in his private life, too. The data collected suggest that even permanent night workers with a high degree of work satisfaction do not usually lose the diurnal orientation of their endogenous clock. Factors other than reorientation of the circadian system may be more important for high tolerance to shift work.

A classification of nursing and midwifery shift systems

A classification of 122 shift systems worked by nurses and midwives in the larger general hospitals (400 + beds) in England and Wales was made. The systems were classified along two main dimensions: the degree of flexibility for shift rostering (either regular, irregular or flexible); and the speed of rotation between night and day work (either a permanent night shift or systems of fast or slow internal rotation). This resulted in nine possible categories of shift systems. The most common shift system was a flexible day shift with a permanent night shift. Other features of the systems are discussed, e.g. the start times and durations of shifts, and the relative influence of flexible rostering on these features. This classification is a prerequisite for a further research project aimed at identifying those features of shift systems which are likely to cause the least detrimental effects for the individual nurses concerned.

Does individual choice determine shift system acceptability?

The relationship between individual control of hours of work and tolerance of shiftwork was examined in a group of nurses and midwives. Two levels of individual control were studied: (i) choosing to work on a regular shift system, e.g. a permanent night shift; and (ii) working on a flexible, rotating shift system where individual choice of shift-sequencing is taken into account. Greater tolerance to shiftwork was found to be associated with more control over hours of work. The advantages of flexible as opposed to irregular shift-rostering, and of choosing to work on a regular permanent night shift were highlighted clearly. The results offer some contribution to the permanent night versus rapidly-rotating shift system debate.

Effects of work organization on the mental health of nursing staff

A survey was carried out among a sample of 973 nurses in hospitals in the Valencian Community (Spain). The aim was to study the relation between work organization, sociodemographic and professional factors and the mental health of nursing staff. The information was collected by means of a questionnaire. Three indicators were used to study mental health: fatigue, sleep disturbance and psychological or psychosomatic indicators of mental suffering. Work organization affected the mental health of workers with varying impact according to the mental health indicator under consideration. Dissatisfaction due to work schedule, psychological and mental load increased the risk of showing signs of fatigue, with a prevalence odds ratio (POR) of 2.15, 2.00, 1.86, respectively, along with the risk of psychological symptoms with a POR of 2.36, 1.80, 2.10, respectively. Permanent night shifts or rotating night shifts increased the risk of sleep disturbance with a POR of 2.00 and 1.34 respectively.

Adaptation to permanent night work: the number of consecutive work nights and motivated choice.

To study the effects of different patterns of days on and days off duty within a permanent night shift schedule, we studied two groups of female permanent night nurses, one (n = 42) working 'many' nights in a row, and the other (n = 36) working 'few' nights in a row. The groups were matched for several important moderating variables. All nurses were interviewed individually, and they answered several questionnaires. A MANOVA revealed no statistically significant differences in subjective health between the two groups. Nor was any difference found for satisfaction measures. The many-night group however seemed to put more effort into dealing with their schedule; they used more active coping, had a higher cigarette consumption, and engaged more in sport. They also stayed one hour less in bed during the day after the last night shift. It is concluded that neither schedule was a clear threat to subjective health because the acceptance of permanent night work was the result of a motivated choice and because social support was high. The differences between the two schedules were not large enough to suggest that one of them should be favoured over the other.

How fast should the night shift rotate? A Rejoinder

The argument for greater use of permanent night shift does not match the three times greater use of rotating three-shift systems in Britain. Studies of industrial production show very slight differences between output on different shifts, unlike laboratory studies, suggesting that it is almost impossible to reproduce the practice, motivation, and real consequences of work in laboratory settings. People who prefer permanent night shift often prefer to avoid management, and few managements welcome this; or have important tasks to perform at home in the day-time. Some studies of adaptation have defined inversion of temperature curves poorly, and most night-workers never completely adapt. Social flexibility, which has been the main attraction of rapidly rotating shifts, can be reproduced on permanent night shifts, but then loses the possibility of adaptation.

Is there a ‘best compromise’ shift system?

In his review Wilkinson considers the question 'How fast should the night shift rotate? He concludes quite strongly that with the possible exception of social factors, most of the evidence favours the use of prolonged or permanent night shifts. In this reply I argue that in reaching this conclusion Wilkinson has (i) overestimated the problems associated with rapidly-rotating shift systems; and (ii) underestimated the problems that might be encountered in trying to implement effective permanent night shift systems. The evidence on the various problems reviewed by Wilkinson is reconsidered. Other aspects of shift systems that were ignored by Wilkinson are then also taken into account. It is concluded that the evidence does not allow a general choice to be made between the use of either permanent night shifts or rapidly rotating, delaying, shift system. Rather the choice between them would appear to depend on the relative importance attached to safety and social problems in any given workplace.

Melatonin rhythms in night shift workers.

For some time, it has remained uncertain whether the circadian rhythms of permanent night shift workers are adapted to their night-active schedule. Previous studies of this question have often been limited by "masking" (evoked) effects of sleep and activity on body temperature and cortisol, used as marker rhythms. In this study, the problem of masking was minimized by measuring the timing of melatonin production under dim light conditions. Nine permanent night shift workers were admitted to the Clinical Research Center (CRC) directly from their last work shift of the week and remained in dim light while blood samples were obtained hourly for 24 hours. Melatonin concentrations were measured in these samples using a gas-chromatographic mass-spectrometric method. Sleep diaries were completed for two weeks prior to the admission to the CRC. Overall, the onset of the melatonin rhythm was about 7.2 hours earlier (or 16.8 hours later) in the night workers compared to day-active controls. It was not possible to know whether the phase of the melatonin rhythm was the result of advances or delays. In night shift workers, sleep was initiated (on average) about three hours prior to the onset of melatonin production. In contrast, day-active subjects initiated sleep (on average) about three hours after their melatonin onset. Thus, the sleep times selected by night shift workers may not be well-synchronized to their melatonin rhythm, assumed to mark the phase of their underlying circadian pacemaker.

Alertness of night nurses: two shift systems compared.

The alertness of hospital trainee nurses during their night shift work was assessed by recording performance at night on an arousal-sensitive unprepared simple reaction time task. One group carried out a number of separate weeks on night shift throughout their three-year course. Here performance fell from first to seventh day of the week on night shift, implying progressive sleep deprivation. Another group covered their night work by a single three-month 'permanent' night shift of four (or three) nights on and three (or four) days off each week. Here initial performance level fell by the 45th night but had returned to normal by the last (90th) night. In both systems individuals varied considerably in their ability to maintain performance during sustained night work. These results strengthen the case for permanent night shifts, with careful selection of personnel, as a means of organizing night nursing in hospitals.

The many meanings of sleep

Abstract Reductions in sleep are concomitant with night shift work. Data are presented showing that these robust differences in sleep are even present in experienced permanent night shift workers who most prefer to work nights. A model is presented which relates these reductions to chronic sleep deprivation. This, in turn, may be associated with performance decrements, and lead to accidents and illness. Better work schedule selection, worker training programs, and preventive medical action are unproven but promising approaches to overturning this model.