Individual differences in tolerance to shiftwork: a review

Individual differences in the subjective health effects of shiftwork are reviewed. Circadian regulation and brain restitution (sleep) are the crucial mechanisms by which inter-individual factors can affect tolerance to shiftwork. On the other hand, shiftworkers can use different coping mechanisms by trying to schedule their lives and especially their sleeping habits to work at unusual hours. Individual factors related to shiftwork tolerance are discussed in two groups; first, the factors which affect primarily the circadian adjustment; and, second, the factors which mainly relate to the ability to sleep at unusual hours. The significance of circadian adjustment in shiftwork tolerance is outlined.     

Main and interactive effects of shiftwork, age and work stress on health in an Italian sample of healthcare workers

Among healthcare workers, shiftwork (mostly if nightwork is also included), ageing and work-related stress may be factors leading to impaired health. Such risk factors may also operate in interaction, resulting in an even increased harm for health. The present study aims at evaluating these relationships in a sample of 1842 hospital workers in Northern Italy. Subjects were mainly women, 33.1% were aged > or = 45 yr, and they were almost evenly distributed between dayworkers and rotating shiftworkers (nights included). Shiftwork was associated with poor sleep, while it was protective against gastrointestinal disorders, poor work ability and job dissatisfaction. Work stress was the risk factor with the highest relevance for poor health. Ageing was associated with lower physical health. Few significant interactions were observed. Shiftwork with nights and high work stress significantly interacted in increasing the risk for poor sleep. The "healthy worker effect" may have played a strong role in study findings.     

Sleep patterns,shiftwork, and individual differences: a comparison of onshore and offshore control-room operators

Abstract

The sleep patterns of offshore control-room operators were compared with those of personnel carrying out similar work onshore, taking into account individual differences in age, number of years of shiftwork, and neuroticism. The dependent variables were self-reported sleep quality and duration for day-shift (D-S) and night-shift (N-S) work, and during leave periods (L-P) Offshore workers reported longer N-S sleep duration, and lower D-S sleep quality than those onshore, but the two groups did not differ in L-P measures. The effects of environmental differences (onshore versus offshore) on sleep patterns were more marked than those of the two different shift systems (weekly rotation and fast rotation) in operation onshore. Age was negatively related to both duration and quality of sleep; over and above age, number of years of shiftwork was negatively related to sleep duration. Neuroticism was also negatively related to sleep duration and, more strongly, to sleep quality. These findings are discussed in relation to the literature on shiftwork and sleep in general, and the characteristics of the offshore environment in particular     

Gender influences on performance,mood and recovery sleep in fatigued aviators

Female aviators now are able to serve in combat roles, but few studies have addressed potential differences between the ability of males and females to withstand combat stressors. This study examined responses of men and women to one operational stressor, sleep deprivation. Pilots were tested on flight performance and mood during 40-h periods of sustained wakefulness. Baseline and recovery sleep also were examined. Gender produced no operationally significant effects on flight performance or recovery sleep. Although mood tests showed that women felt less tense and more energetic than men, there were no interactions between sleep deprivation and gender on either flight performance or psychological mood.     

The relationship between circadian,personality, and temperament characteristics and attitude towards shiftwork

This study aimed to find out whether and to what extent circadian and personality characteristics contribute in determining attitude towards shiftwork. Two groups of female steel plant shift- (n = 54) and dayworkers (n = 54) were matched for age, job tenure, marital status, number, and age of children. The control group was made up of 2 subgroups of dayworkers with (n = 29) and without (n = 25) shiftwork experience. The subjects answered questionnaires on morningness, flexibility, languidity, neuroticism, extroversion, reactivity, and attitude towards shiftwork. Correlation analysis and multiple regression analysis were performed on the data of experimental group and control subgroups separately. Amongst current shiftworkers, the best predictors of attitude towards shiftwork were flexibility of sleeping habits and the ability to overcome drowsiness. Amongst former shiftworkers attitude was determined primarily by reactivity, but in the dayworkers without shiftwork experience no predictors of the attitude were found. The results imply that circadian and personality characteristics related to shiftwork adjustment contribute in determining attitude towards shiftwork.     

Biological and psychological responses to two rapid shiftwork schedules

This study presents the biological responses to shiftwork in two groups of workers with different shiftwork rotas. Biological responses were studied by recording the heart rate and the changes in the circadian profile of salivary cortisol over 24?h (RIA assays). Various items were recorded through questionnaires aimed at determining self appreciation of sleep quantity, stress, health, satisfaction at work and in private lives. Thirty two male subjects aged from 23 to 56, working for the same company, having given their informed consent, took part in the study. The study was carried out under realistic conditions (at the work place) under the control of an occupational physician. Sixteen day-workers (8 am?–?6?pm) served as a reference group. Eight shiftworkers included in alternate schedules (morning M 4 am?–?12 am, evening E 12 am?–?8?pm, night N 8?pm?–?4 am) according to a system M, S, N 3/2, (3 work, 2 rest) and eight according to a system 7/5 (3M/2S/2N/5R, 2/3/2/5, 2/2/3/5) constituted the groups of shiftworkers respectively named 3/2 and 7/5. All subjects had comparable ages and BMIs. Shiftworkers expressed a higher stress level and frequency of health problems and a lower satisfaction at work than the control. Among the three groups, the 7/5 group had the best health and fitness score and was in need of less sleep. Heart rate was not affected by shift work. Conversely, consistent changes appeared in cortisol circadian profiles, the greatest changes appearing for the night shift and among the two groups of shiftworkers, more particularly for the 7/5 group. These changes correlated with self-perceived constraints of work and showed the difficulties of adaptation to shiftwork.     

The reliability and stability of various individual difference and tolerance to shiftwork measures

The aim of the study was to evaluate the reliability and temporal stability of various individual difference and tolerance to shiftwork measures which were used in an extensive study on relationships between shiftworkers' features and tolerance to shiftwork. The study was conducted in a Croatian oil refinery where 604 male shift workers, working in a 2:2:3 continuous three-shift system were examined by means of various questionnaires. A subsample of 61 shift workers were re-examined using the same questionnaires and the same administration procedure nine years later. The questionnaires were: Jenkins Activity Survey, Eysenck Personality Inventory, Momingness-Eveningness Questionnaire, Behavioural Arousal Questionnaire, Orcadian Type Questionnaire and Inventory, Way of Life Questionnaire, Health Information Questionnaire, Sleep Quality Scale. The questionnaires were scored for 14 individual difference measures and eight tolerance to shiftwork measures. In addition to these scores sleep durations on night, morning, afternoon shifts, and on days off were used as tolerance to shiftwork measures. The reliability of each measure was determined by means of Cronbach alpha coefficients computed on a total of 604 shiftworkers and temporal stability by means of correlation coefficients between the scores obtained on two occasions on the subsample of 61 shiftworkers. The internal consistency coefficients for most of the measures ranged between moderate to high, and were considered to be satisfactory. The correlations between the scores obtained twice over a period of nine years proved both the individual difference and tolerance to shiftwork measures to be temporally stable. The only measure that had insignificant correlation was the sleep duration on days off.     

A field study of sleep and fatigue in a regular rotating 12-h shift system

The aim of this study was to examine a regular rotating 12-h shift system (2D2N4Off) at an Australian Smelter. Sleep behavior, subjective fatigue and neurobehavioral performance were investigated over a 14-day period for 20 employees. Activity monitors, sleep/wake diaries, and 5-min psychomotor vigilance tasks were used. Sleep data showed differences between day and night shifts. While sleep prior to night1 was increased relative to day shifts, a reduced sleep length carried into the period leading to night2. Total wakefulness at the end of shift, and subjective fatigue were increased for night shifts, particularly night1. Decrements in performance data supported these findings. Both prior wakefulness and prior sleep are important in a 12-h shift system. Employees may “sleep in” after day shifts, rather than taking extra sleep prior to night work. Thus, sleep between day and night shifts is based on recovery rather than preparation.     

Individual differences in circadian rhythm parameters and short-term tolerance to shiftwork: a follow-up study

The relationship between individual differences in the phase and amplitude of circadian rhythms and tolerance to shiftwork has been the subject of several studies. Those studies recorded circadian rhythms and shiftwork tolerance at approximately the same time. The present study aimed to examine the predictive relationships between the amplitude, phase, and mesor of 24 h rhythms obtained before exposure to shiftwork, and subsequent indices of tolerance measured after one and three years of shiftwork. The results revealed some stable relations between the various rhythm parameters and subsequent tolerance measures. Workers who had a higher mesor of positive moods, and a lower mesor of negative moods and fatigue, before entering shiftwork tended to tolerate shiftwork better. Further, those whose heart rate rhythm showed an earlier acrophase had better subsequent sleep quality scores, while those with a smaller amplitude of their temperature, negative mood and fatigue rhythms showed better night-shift tolerance.     

Educational programmes for shiftworkers,their families,and prospective shiftworkers

The concept of educational programmes for shiftworkers has good face validity, but research verification is not evident in the literature. Efforts to date to provide users with extensive information are commendable, but they do not appear to be adequate for the education of shiftworkers. In some cases, this information may impede, distract, or mislead users. As a response to these deficits, seven principles are proposed to guide the designing of educational programmes for shiftworkers. These principles focus on the process of designing programmes, rather than on the specific behavioural techniques or variables to be used. Together, these principles form a process theory. This theory requires validity testing, and can serve as a useful guide for the design of shiftworker educational programmes.     

Sleep in a live-in mining operation: The influence of start times and restricted non-work activities

The amount of sleep obtained between shifts is influenced by numerous factors including the length of work and rest periods, the timing of the rest period relative to the endogenous circadian cycle and personal choices about the use of non-work time. The current study utilised a real-world live-in mining environment to examine the amount of sleep obtained when access to normal domestic, family and social activities was restricted. Participants were 29 mining operators (26 male, average age 37.4 ± 6.8 years) who recorded sleep, work and fatigue information and wore an activity monitor for a cycle of seven day shifts and seven night shifts (both 12 h) followed by either seven or fourteen days off. During the two weeks of work participants lived on-site. Total sleep time was significantly less (p < 0.01) while on-site on both day (6.1 ± 1.0 h) and night shifts (5.7 ± 1.5 h) than days off (7.4 ± 1.4 h). Further, night shift sleep was significantly shorter than day-shift sleep (p < 0.01). Assessment of subjective fatigue ratings showed that the sleep associated with both days off and night shifts had a greater recovery value than sleep associated with day shifts (p < 0.01). While on-site, participants obtained only 6 h of sleep indicating that the absence of competing domestic, family and social activities did not convert to more sleep. Factors including shift start times and circadian influences appear to have been more important.     

Balancing shiftwork and life outside work: do 12-h shifts make a difference?

Twelve-hour shifts are a popular alternative to 8-h shifts as many consider these shift arrangements superior in terms of facilitating a better social and family life. This view is largely based on anecdotal evidence, however as few studies have examined longitudinal relations between work/non-work conflict and shift length. Using self-report data from 137 machine operators, this study examined whether 8- and 12-h shifts have a differential impact on work/non-work conflict. Relationships between work/non-work conflict and subjective health were also examined. Profile analysis revealed no significant relationships between shift length and work/non-work conflict. Results of regression analyses indicated that work/non-work conflict was positively related to psychological health on 8 and 12-h shifts (p<.01) but not to physical health. These results suggest that 12-h shifts did not offer any benefits or disadvantages for workers trying to reconcile their work and non-work life during the 13-month study period.     

A polysomnographic study of morning and afternoon sleep quality during simulated night shift work

Shiftworkers differ as to scheduling their day sleep between night shifts. An experimental study was carried out to compare the effects of morning and afternoon sleep behaviour on sleep quality within and after a period of seven night shifts. Twelve young males participated in a repeated–measures design, six sleeping in the morning and six in the afternoon after night shifts. Sleep quality was evaluated by polysomnographic and subjective measures. Morning and afternoon sleepers showed some differences in the trend of sleep changes over successive sleep periods. However, at the end of the night shift week, there were no marked differences in sleep quality. Both morning and afternoon sleep were characterized by deep sleep, and short sleep onset latencies.     

Sleep and circadian rhythms in mining operators: limited evidence of adaptation to night shifts

Cumulative sleep deprivation is often associated with work patterns involving night shift or early morning shifts. Adaptation of the circadian system to the shift pattern is reported to promote improved duration and quality of sleep and a concurrent improvement in performance. The current study followed twenty-nine operators at a live-in mining operation working to a seven-day, seven-night shift pattern who collected saliva samples for melatonin measurement, recorded sleep using activity monitors and diaries, and underwent performance testing (psychomotor vigilance task) for one complete roster cycle. The time of onset of melatonin secretion changed significantly (P=0.022) across the week of both Day and Night shifts (2104 h ± 16 min versus 2130 h ± 16 min, respectively), but the small magnitude of the change indicates a lack of true circadian rhythm adaptation to the lifestyle. Total sleep time was longer following the seventh Day shift (associated with a period of 24 h off prior to the commencement of Night shifts). There were no other changes in total sleep time. Further, there were no improvements in sleep onset latency or sleep efficiency on Day or Night shifts. However, reaction times recorded at the end of the shifts slowed across the seven Day and seven Night shifts indicative of impairments in psychomotor performance (F(6,168)=6.087, P<0.001). The results suggest that previous reports of adaptation to consecutive night shifts cannot necessarily be applied to onshore or Australian environments. Adaptation is dependent on factors such as light exposure, environmental conditions, shift parameters such as wake-up, work start and work end times and individual characteristics.     

Gender, identity and CMC

This paper re‐examines a number of recent discussions of computer‐mediated communication (CMC) in the light of debates concerning gender, identity and inequality. There have been many claims made by disparate groups and institutions, from educators and technologists, through to the advertising of communications companies, which have claimed that CMC‐based interactions lack the overt structures of inequality found in other communicative situations. This ideology of 'on‐line equality' is partly based upon a number of research findings, as well as popularised accounts of 'life on the screen'. Set against this is a growing body of research into CMC and gender, as well as other structures of inequality, which has made apparent the differences in both access and practice. By re‐examining the various claims underlying both positions, as well as deploying recent research into the cultural aspects of gender identities, this paper aims to make clear the centrality of gender to CMC interactions.     

Nutrition and shiftwork: the use of meal classification as a new tool for qualitative/quantitative evaluation of dietary intake in shiftworkers

Established nutritional science methods and a new concept for meal–classification were applied to shiftworker (rotating 3-shift) data. The frequency of meals and snacks of different nutritional quality as a function of work schedule was evaluated, as well as the content of selected nutrients (energy, fat, sucrose, dietary fibres, ascorbic acid) in these meals and snacks. The results do not indicate that rotating 3-shift work affects the nutritional quality of the diet or the frequency of different types of meals and snacks. A qualitative classification of meals and snacks might be a cost–effective strategy for data–evaluation in field studies of shift workers' eating habits when quantitative estimations of the dietary intake are to be complicated.     

Locomotive engineers and their spouses: coffee consumption,mood, and sleep reports

Locomotive engineers (train drivers) on irregular work schedules reported a general coffee consumption rate higher than that reported by a comparison sample of permanent shift factory workers. The present study examines the impact of this consumption on workday and non-workday sleep behaviour and mood ratings. Twenty-seven engineers and their spouses each completed daily logs for 30 consecutive days. Daily logs were then sorted into workday and non-workday categories. Workday sleep length was significantly shorter than non-workday sleep length for both engineers and spouses. For the engineers only, coffee consumption on workdays was higher than on non-workdays. This increased coffee consumption was correlated with longer sleep latency, increased negative mood, and decreased positive mood on both work and non-workdays. This was not true for spouses. These results may be related to a days-off carry-over effect of caffeine or a general consumption behaviour characteristic.     

Dissecting circadian performance rhythms: implications for shiftwork

Safety on shift systems will depend, at least in part, on the adjustment of shiftworkers' circadian (c.24h) rhythms in performance capabilities which will in turn depend on their underlying control. In the present study three volunteers lived on a 30h ‘day’ and performed a range of tasks every 2h (while awake) to allow estimates of the relative magnitude of the endogenous (body clock) and exogenous (masking) components of their rhythms to be made. Performance rhythms were found to differ considerably in this respect with, for example, speed on a 4–choice serial reaction time task appearing to be largely endogenously determined while that on a 5–target Sternberg task was more dependent on exogenous (i.e., 30h) factors. This implies that performance measures may adjust at very different rates to one another to night work, and hence that the optimal form of shift system may vary according to the precise demands of the shiftworker's task.     

Individual differences in night and continuously-rotating shiftwork: seeking anticipatory rather than compensatory strategy

Individual differences in adaptation to night or continuously-rotating shiftwork may reflect distinct strategies of coping with temporal challenges of the environment. Rather than studying compensatory mechanisms, we have chosen the anticipatory response of the sleep onset time preceding work in order to reveal the strategy used by workers submitted to those shift systems including night work. Comprehensive interviews, taking into account several aspects of the workers' lives, allowed for a classification of the subjects in terms of adaptation to their working schedules. Night workers go to bed once a day, whereas shiftworkers prefer to allocate their sleep onsets to two different periods of the day. For both cases, the more well-adapted an individual is, according to the classification obtained by the interviews, the more regular will be the choice of sleep onset times.     

Performance and alertness on 8 h and 12 h rotating shifts at a natural gas utility

Abstract

An 8 h/5-7 day shift schedule was compared with a newly instituted 12 h/2-4 day schedule in this, our second worksite study of extended workshifts. Workers completed a performance/alertness test battery, and a questionnaire on sleep patterns and other personal habits, 2-4 times a week on all shifts. After 10 months adaptation to the 12 h shift schedule, there were decrements in performance/ alertness attributable to the extra 4 h on the extended shift. There were also reductions in sleep across the workweek which were most apparent on 12 h night shifts. The results are consistent with our first worksite study of 12 h shifts and indicate extra caution should be exercised when scheduling critical activities for extended workshifts, especially extended night shifts.