Comparing the acute effects of shiftwork on mothers and fathers.

BACKGROUND: Shift work may impact women more negatively than men due to the increased burden of coping with demanding work schedules while also undertaking more of the domestic chores, including childcare. AIMS: To examine whether the combination of shift working and caring for children affects the sleep, fatigue and work-family conflict experienced by women more than it affects men. METHODS: Using data from a survey of the Swedish working population, mixed linear regression models examined work schedule (daywork, shift work with nights, shift work without nights), gender and presence of children <13 years at home as predictors of sleep insufficiency, sleep disturbance, fatigue and work-family conflict, over up to three successive measurement occasions. Adjustments were made for age, education, full/part-time working and baseline year. RESULTS: In fully adjusted models (N = 8938), shift work was associated with insufficient sleep (P < 0.01), disturbed sleep (P < 0.01), fatigue (P < 0.05) and work-family conflict (P < 0.001). Interactions in the analyses of sleep disturbance (P < 0.001) and work-family interference (P < 0.05) indicated that among participants with no children, females reported more disturbed sleep and more work-family conflict than their male counterparts, irrespective of schedule; while among participants with children, female dayworkers reported more disturbed sleep than their male counterparts, and females working shifts without nights reported more work-family interference. CONCLUSIONS: Having young children did not exacerbate negative effects of shift work, in either men or women. This may reflect high levels of gender equality and childcare provision in Sweden.

The impact of work time control on physicians' sleep and well-being.

Physicians' work schedules are an important determinant of their own wellbeing and that of their patients. This study considers whether allowing physicians control over their work hours ameliorates the effects of demanding work schedules. A questionnaire was completed by hospital physicians regarding their work hours (exposure to long shifts, short inter-shift intervals, weekend duties, night duties, unpaid overtime; and work time control), sleep (quantity and disturbance) and wellbeing (burnout, stress and fatigue). Work time control moderated the negative impact that frequent night working had upon sleep quantity and sleep disturbance. For participants who never worked long shifts, work time control was associated with fewer short sleeps, but this was not the case for those who did work long shifts. Optimizing the balance between schedule flexibility and patient needs could enhance physicians' sleep when working the night shift, thereby reducing their levels of fatigue and enhancing patient care.

Sleep disturbances, work stress and work hours: a cross-sectional study.

OBJECTIVE: The study examined the multivariate relationship between disturbed sleep and different work-related and background/life style factors. METHODS: 5720 healthy employed men and women living in the greater Stockholm area participated. A factor analysis of eight items provided one main factor: "disturbed sleep." The data were analyzed using a multiple logistic regression analysis against the index disturbed sleep as well as the separate items "not well rested" and "difficulties awakening." RESULTS: The results showed that high work demands [odds ratio (OR) = 2.15] and physical effort at work (OR = 1.94) are risk indicators for disturbed sleep, while high social support is associated with reduced risk (OR = 0.44). In addition, higher age (45+), female gender, a high body mass index (BMI) and lack of exercise are background/life style risk indicators. Introducing into the model an item representing inability to stop thinking about work during free time yielded the highest OR (3.20) and forced work demands out of the regression. With regard to not feeling well rested, the same significant predictors, except physical effort, were obtained, as well as for having night work and being married. In addition, the age effect was reversed--high age predicted reduced risk of not feeling well rested. Difficulties awakening was predicted by high work demands, low social support, being male, low age and smoking. It is notable that, whereas subjective sleep quality decreased with age, the difficulties awakening and feelings of not being well rested after sleep increased with age. CONCLUSION: It was concluded that stress and the social situation at work are strongly linked to disturbed sleep and impaired awakening, that gender and, even more so, age may modify this and that the inability to stop worrying about work during free time may be an important link in the relation between stress and sleep.

Work organisation and unintentional sleep: results from the WOLF study.

BACKGROUND: Falling asleep at work is receiving increasing attention as a cause of work accidents. AIMS: To investigate which variables (related to work, lifestyle, or background) are related to the tendency to fall asleep unintentionally, either during work hours, or during leisure time. METHODS: 5589 individuals (76% response rate) responded to a questionnaire. A multiple logistic regression analysis of the cross sectional data was used to estimate the risk of falling asleep. RESULTS: The prevalence for falling asleep unintentionally at least once a month was 7.0% during work hours and 23.1% during leisure time. The risk of unintentional sleep at work was related to disturbed sleep, having shift work, and higher socioeconomic group. Being older, being a woman, and being a smoker were associated with a reduced risk of unintentionally falling asleep at work. Work demands, decision latitude at work, physical load, sedentary work, solitary work, extra work, and overtime work were not related to falling asleep at work. Removing "disturbed sleep" as a predictor did not change the odds ratios of the other predictors in any significant way. With respect to falling asleep during leisure time, disturbed sleep, snoring, high work demands, being a smoker, not exercising, and higher age (>45 years) became risk indicators. CONCLUSION: The risk of involuntary sleep at work is increased in connection with disturbed sleep but also with night work, socioeconomic group, low age, being a male, and being a non-smoker.

Age, gender and early morning highway accidents.

Accident register data, time budget studies and road traffic flow data were used to compute the age and gender-dependent relative risk [odds ratio (OR)] of being involved in a driving accident in which the driver was injured or killed. Alcohol-related accidents were excluded from the analysis. The results showed that the night-time risk, compared with that of the forenoon, was dramatically increased (OR=5) for young drivers (18--24 years) and reduced for old (65+) drivers. In direct comparison, the young drivers had 5-10 times higher risk of being involved in an accident during late night than during the forenoon, with the excess risk during the daytime being considerably lower. Women had a less pronounced night-time peak than men. In direct comparison, men had twice as high a risk as women during the late night hours. The results clearly demonstrate a strong effect of young age on night-time accident risk, together with a moderate effect of (male) gender.

Night driving, season, and the risk of highway accidents.

Official accident and traffic density statistics on Swedish highways were used to compute the relative risk (Odds Ratio - OR) of being injured or killed in a traffic accident at different times of day. After removing accidents due to alcohol 10344 accidents remained for computations, and the period 10:00h-11:00h was used as the reference point. The highest total risk was seen at 0400h (OR=5.7, Confidence interval = 5.6-5.8), with an OR of 11.4 (Ci=10.3-12.5) for fatal accidents at the same point. The same pattern was exhibited by single vehicle, head-on, and "other" (e.g., turning off the road) accidents, whereas overtaking and rear-end accidents did not show clear 24 hour patterns. Retaining alcohol-related accidents approximately doubled the nighttime peak for total accidents. During the winter, the peak of total accidents occurred at 03:00h (OR=3.8, Ci=3.5-4.0), five hours before sunrise, whereas the summer peak occurred at 04:00h (OR=11.6, Ci=11.3-11.9), shortly after the early summer sunrise and with consistently higher nighttime risk than for winter driving. It was concluded that early morning driving is several times more dangerous than driving during the forenoon. Apart from alcohol the effect seems related to sleepiness, but not to darkness.

The effects of double-shifts (15.5 hours) on sleep, fatigue and health.

The aim of the present study was to investigate how "double-shifts" (15.5 hours) affects sleep, fatigue and self-rated health. The study was carried out on male construction workers of which 80% were long-distance commuters. The schedule involved two work periods and each work period involved two double shifts in a row. The subjects filled in a sleep/wake diary at 8 times across a year and a questionnaire at 3 times. They also wore an actigraph during one shift cycle. The results showed that sleepiness, and to a certain extent, mental fatigue increased during double shifts and accumulated across days. The short rest time (8.5 hours) between days caused insufficient sleep and approximately 5.5 hours of sleep was obtained between double shifts. Questionnaire data showed that complaints of insufficient sleep, exhaustion on awakening and pain symptoms increased across the year. It was concluded that a shift system involving double shifts has a negative effect on fatigue, recovery and health-related well-being.

A 6-hour working day--effects on health and well-being.

The effect of the total amount of work hours and the benefits of a shortening is frequently debated, but very little data is available. The present study compared a group (N = 41) that obtained a 9 h reduction of the working week (to a 6 h day) with a comparison group (N = 22) that retained normal work hours. Both groups were constituted of mainly female health care and day care nursery personnel. The experimental group retained full pay and extra personnel were employed to compensate for loss of hours. Questionnaire data were obtained before and 1 year after the change. The data were analyzed using a two-factor ANOVA with the interaction term year*group as the main focus. The results showed a significant interaction of year*group for social factors, sleep quality, mental fatigue, and heart/respiratory complaints, and attitude to work hours. In all cases the experimental group improved whereas the control group did not change. It was concluded that shortened work hours have clear social effects and moderate effects on well-being.

Bright light treatment used for adaptation to night work and re-adaptation back to day life. A field study at an oil platform in the North Sea.

Night workers complain of sleepiness, reduced performance and disturbed sleep due to lack of adjustment of the circadian rhythm. In simulated night-work experiments scheduled exposure to bright light has been shown to reduce these complaints. Here we studied the effects of bright light treatment on the adaptation to 14 days of consecutive night work at an oil platform in the North Sea, and the subsequent readaptation to day life at home, using the Karolinska sleep/wake diary. Bright light treatment of 30 min per exposure was applied during the first 4 nights of the night-shift period and the first 4 days at home following the shift period. The bright light exposure was scheduled individually to phase delay the circadian rhythm. Bright light treatment modestly facilitated the subjective adaptation to night work, but the positive effect of bright light was especially pronounced during the re-adaptation back to day life following the return home. Sleepiness was reduced and the quality of day was rated better after exposure to bright light. The modest effect of bright light at the platform was, possibly, related to the finding that the workers seemed to adapt to night work within a few days even without bright light. These results suggest that short-term bright light treatment may help the adaptation to an extended night-work period, and especially the subsequent re-adaptation to day life.

Rapid adaptation to night work at an oil platform, but slow readaptation after returning home.

Previous research indicates that night workers' circadian rhythms do not adapt to night work and that disturbed sleep and wakefulness persist, even after weeks of working on night shift. We studied adjustment to 14 days of consecutive night work at an oil platform and the readjustment to day life at home, using the Karolinska sleep/wake diary. The platform workers adapted to night work within a few days, as indicated by the rapid reduction of night-work sleepiness, and by the gradual delay of bedtime to an hour commensurate with the behavior of day workers. Readaptation to day life was slower and more difficult, adding evidence of a complete adaptation to night work. We conclude that the lack of conflicting exposure to daylight in the morning may have facilitated the rapid adjustment to night work.

Effects of alternating 8- and 12-hour shifts on sleep, sleepiness, physical effort and performance.

OBJECTIVES: The aim of the present study was to compare 12-hour shifts during weekends with 8-hour shifts during weekdays with respect to sleep, sleepiness, physical effort, and performance. METHODS: Thirty-one subjects at a power plant participated. Sleep, sleepiness, and physical effort were measured with a diary. About half of the subjects carried out a reaction-time test during both 8- and 12-hour morning and night shifts. The remaining subjects carried out a vigilance task. RESULTS: Sleepiness was higher and physical effort lower on the 12-hour night shift than on the 8-hour night shift. However, the subjects who had the same level of physical effort on 8- and 12-hour night shifts did not differ with respect to sleepiness. During the 12-hour morning shift, sleepiness was lower and the sleep length was longer than on the 8-h morning shift. The subjects who had the same amount of sleep for 8- and 12-hour morning shifts showed no difference in sleepiness. Sleep did not differ between 8- and 12-hour night shifts. There was no difference between 8- and 12-hour shifts with respect to performance. CONCLUSIONS: It was suggested that the difference in sleepiness between 8- and 12-hour shifts is related to differences in sleep length for the morning shift, and to differences in physical effort for the night shift, rather than to shift duration. Thus the most likely conclusion is that 12-hour shifts do not cause increased sleepiness or impaired performance or disturbed sleep.

Change from an 8-hour shift to a 12-hour shift, attitudes, sleep, sleepiness and performance.

OBJECTIVES: The present study sought to evaluate the effect of a change from a rotating 3-shift (8-hour) to a 2-shift shift (12 hour) schedule on sleep, sleepiness, performance, perceived health, and well-being. METHODS: Thirty-two shift workers at a chemical plant (control room operators) responded to a questionnaire a few months before a change was made in their shift schedule and 10 months after the change. Fourteen workers also filled out a diary, carried activity loggers, and carried out reaction-time tests (beginning and end of shift). Fourteen day workers served as a reference group for the questionnaires and 9 were intensively studied during a week with workdays and a free weekend. RESULTS: The questionnaire data showed that the shift change increased satisfaction with workhours, sleep, and time for social activities. Health, perceived accident risk, and reaction-time performance were not negatively affected. Alertness improved and subjective recovery time after night work decreased. The quick changes in the 8-hour schedule greatly increased sleep problems and fatigue. Sleepiness integrated across the entire shift cycle showed that the shift workers were less alert than the day workers, across workdays and days off (although alertness increased with the 12-hour shift). CONCLUSIONS: The change from 8-hour to 12-hour shifts was positive in most respects, possibly due to the shorter sequences of the workdays, the longer sequences of consecutive days off, the fewer types of shifts (easier planning), and the elimination of quick changes. The results may differ in groups with a higher work load.

Sleep in a truck berth.

The aim of the present pilot study was to study the effects of sleep in a truck berth. Experiment A included eight subjects who slept during two conditions (laboratory and in a truck berth during quiet conditions). Experiment B included two conditions (truck-berth sleep during quiet and noisy/disturbed conditions, respectively); six subjects participated. Polysomnography was recorded and ratings of sleep quality and postsleep sleepiness were made. During the truck-berth conditions, noise was continuously recorded. When two-tailed t tests were used, the results showed no significant effects (alpha level = 0.05) for any of the experiments. However, when one-tailed tests were used, experiment A showed a longer rapid eye movement (REM) latency for the truck-berth condition. Experiment B showed less-refreshing sleep for the disturbed condition (one-tailed test). The noise level was significantly higher during the disturbed condition. The results showed that electroencephalograph (EEG)-recorded sleep was not affected by sleeping in a truck, even when the truck was parked at a noisy location (truck terminal). However, considering some limitations of the experiments, for example small sample size, lack of adaptation night, etc., the present results should be interpreted with some caution and need to be replicated.

Morning work: effects of early rising on sleep and alertness.

The aim of the present study is to investigate how early morning work affects sleep and alertness. Twenty-two females, employed as airline cabin crew members, participated in the study. The design included two sleep conditions (work day and free day) for an early group and for a control group. The results show that early morning work reduced sleep to 5 hours and 12 minutes and that the reduction of sleep consisted of less stage 2 and rapid eye movement (REM) sleep. However, when the analysis was restricted to the first 5 hours, no differences in sleep stages, arousals, or sleep continuity were obtained between groups or conditions. Analysis of electroencephalogram (EEG) power density for the 0.5-16.5 Hz bands across nonREM periods showed no differences. With respect to the subjective ratings, early morning work was associated with more apprehension of difficulties in awakening and insufficient sleep. Daytime alertness and ease of awakening did not differ between groups, but the early group had significantly more sleepiness and complained more of unrefreshing sleep in connection with the work day compared to the free day. Ratings of insufficient sleep and high daytime sleepiness were mainly predicted (multiple regression analyses) by short total sleep time (TST), whereas apprehension of an unpleasant awakening was predicted by an early wake-up time. It was concluded that early morning work causes a reduction of sleep time and an increase in apprehension stress.

The effects of a short daytime nap after restricted night sleep.

Eight subjects participated on three occasions in a study investigating the effect of a 30 minute daytime nap opportunity on alertness/sleepiness. The baseline condition was a normal home sleep (7.5 hours, with bedtime at 2300 hours). Sleep during the other two conditions was between 2400 hours and 0400 hours. During one of the two 4-hour conditions, a short nap was allowed (between 1045 hours and 1115 hours). Self-ratings of sleepiness/alertness (Karolinska Sleepiness Scale) were recorded every hour. At 10, 12, and 15 hours, the subjects performed a 28-minute visual vigilance task. Electroencephalograms (EEG) and electrooculograms (EOG) were recorded continuously, including during a 10-minute standardized recording procedure at the beginning of each day. Mean total sleep time during the nap was 19.8 (standard error 2.4) minutes. Compared to baseline, EEG/EOG sleepiness and subjective sleepiness were significantly higher and vigilance performance at 10 hours lower, respectively, after the two short sleeps. The nap brought performance to baseline levels, and subjective sleepiness decreased significantly. It was concluded that the short nap had a clear positive effect on alertness.

Sleepiness and performance of professional drivers in a truck simulator--comparisons between day and night driving.

Previous research has shown that night driving performance may be seriously affected by sleepiness. The present study compared daytime and night-time performance of professional drivers on a simulated truck driving task. A secondary purpose was whether a nap or a rest pause would affect performance. Nine professional drivers participated in a counterbalanced design. The conditions were day driving (DAYDRIVE), night driving (NIGHTDRIVE), night driving with a 30 minute rest (NIGHTREST), and night driving with a 30 minute nap (NIGHTNAP). Each condition consisted of three consecutive 30-min periods. For the DAYDRIVE and NIGHTDRIVE all periods were spent driving while the second period was either a rest pause or a nap for the other two conditions. Mean speed, standard deviation of speed and, standard deviation for lane position were recorded. Self ratings of sleepiness were obtained before and after each 30-min period. Reaction time tests and 10 minute standardized EEG/EOG recordings were obtained before and after each condition. EEG/EOG were also recorded continuously during driving. The effects on driving were small but significant: night driving was slower, with a higher variability of speed, and had higher variability of lane position. Subjective and EEG/EOG sleepiness were clearly higher during the night conditions. Reaction time performance was not significantly affected by conditions. Neither the nap nor the rest pause had any effect.

Effects of timing of shifts on sleepiness and sleep duration.

This review summarizes the effects on sleep duration and sleepiness of (1) the timing of shifts (start and finishing times) and (2) the scheduling of free time between shifts. The results from the few studies available show that sleep duration is clearly determined by the change over time between the night and the morning shift-no more than 5 or 6 hours of sleep is obtained before the morning shift if the shift starts at 06.00 hours or earlier. Therefore, it is suggested that the morning shift should not start before 07.00 hours. A late start of the morning shift will however, increase the sleepiness at the end of the night shift, as well as decrease the duration of the daysleep after the night shift. On the other hand, one may argue that the short daysleep after a night shift may be compensated for by an evening nap, whereas a short night sleep before a morning shift cannot (no time for nap). The review of studies concerning free time between shifts suggests that at least 16 hours is needed and that quick change-overs should be avoided. The free time after a spell of night shifts should be at least 48 hours since the shiftworker needs two main sleep episodes to recover from night work.

Relations between performance and subjective ratings of sleepiness during a night awake.

The present study validated the nine-point Karolinska Sleepiness Scale (KSS) and the new Accumulated Time with Sleepiness (ATS) scale against performance of laboratory tasks. The ATS scale was designed as a method for integrating subjective sleepiness over longer time periods. The subjects were asked if certain symptoms of sleepiness had occurred and, if so, for how long. Six subjects participated twice. Each time they were kept awake during the night (except for a short nap occurring during one of the nights in a counterbalanced order) and were tested at 2200, 0200, 0400 and 0600 hours. The tests included a 10-minute rest period, a 28-minute visual vigilance task and an 11-minute single reaction time task. KSS and visual analogue scale (VAS) ratings were given before each test, and ATS ratings were given after. Performance deteriorated clearly, and all three rating scales reflected increased sleepiness with time of night. Scores on the KSS and VAS showed high correlations with performance tasks (mean intraindividual correlations were between 0.49 and 0.71). Performance correlated even higher with the ATS ratings (r = 0.73-0.79). Intercorrelations between rating scales were also high (r = 0.65-0.86). It was concluded that there were strong relations between ratings of sleepiness and performance, that the ATS rating scale was at least as good as the other scales and that the ratings were affected by type of task.

Sleepiness in long distance truck driving: an ambulatory EEG study of night driving.

Eighteen truck drivers had their EEG recorded continuously during a night or evening drive between southern Sweden and Stockholm (500 km). They also carried out self ratings of sleepiness and performance every hour. The EEG was subjected to spectral analysis. The drivers were divided into two groups with a night group (n = 7) who drove between 20:30 to 97:20 and an evening group (n = 11) who drove between 18:20 and 04:00. The night group showed higher subjective sleepiness and lower subjective performance, and increased alpha and theta burst activity during the last three hours of the drive. The groups did not differ for the first 2-3 h of the drive. For the night group, a significant intraindividual correlation was found between subjective sleepiness and EEG alpha burst activity. End-of-the-drive subjective sleepiness and alpha burst activity were significantly correlated with total work hours and arrival time but not with age, diurnal type, prior (rated) sleep length, total break time, drive time or prior time awake. A regression analysis showed that total work hours and total break time predicted 66% of the variance of alpha burst activity during the end of the drive.

The pattern of slow wave activity in spontaneously occurring long sleep.

The aim of the present study was to estimate the time course of slow wave activity (SWA) in naturally occurring long sleep episodes (ad lib). Sixteen male shift workers were subjected to 24 h ambulatory polysomnography in connection with an afternoon shift. The EEG was subjected to spectral analysis (FFT) as well as to traditional sleep stage scoring. SWA (0.5-4.5 Hz band, both nonREM and REM sleep) declined exponentially and reached an asymptote by the fifth or sixth sleep cycle. However, half the subjects showed a reduced SWA in the first cycle, with a subsequent recovery in the second cycle. The SWA reduction of the first cycle was associated with a reduced REM-latency and it was suggested that uncontrolled external influences of the real life settings may have affected SWA in the first cycle. It was concluded that the decline of SWA across time may deviate from an exponential shape under real life conditions.