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.     

Sleep Disturbances Among Female Nurses: Comparing Shift to Day Work

Recently, attention has focused in Israel on the possible legal and health consequences of shift work. We decided to study sleep disorders among female nursing personnel working a shift schedule, in comparison with day nurses, in a large metropolitan general hospital. The study population was composed of 131 female certified nurses working shifts and 44 working days only. Inclusion criteria for the survey was at least 1 year of shift work alternating between day, evening, and night shifts, or at least 1 year of day work. All participants completed a self-report sleep questionnaire encompassing (a) demographic data, (b) sleep survey, and (c) employment details. Statistical analysis was performed using the Pearson correlation test and analysis of variance multiple range test (according to Scheffe's procedure). No significant correlation was found between sleep disorders and age of subjects. No sleep disorders were reported by 19.8% of shift workers versus 76.5% of day workers. Statistically significant findings were that the number of shifts per week >4.1 (p = 0.001) and duration of shift work >13.6 years (p = 0.007) correlated with the presence of sleep disorders. An additional significant finding (p = 0.014) was the impact of evening shifts on sleep disorders. The present small study confined to women supports the growing body of data on sleep complaints among shift workers.     

Occupational stress and work efficiency of nursing staff engaged in rotating shift work

Occupational stress and stress-related performance impairment is a common feature among hospital nurses engaged in rotating shift work, particularly night work. This cross-sectional survey determined workplace stress and cognitive efficiency of nursing staff engaged in rotating shift work. One hundred twenty-two full-time staff nurses in three different government hospitals in West Bengal, India, were the participants. Perceived exertion, alertness, sleep duration and various performance tests were performed. Sleep duration was least between repeated night shifts in comparison with the other shifts. Though alertness and performance of the staff nurses varied on different shifts, the late portion of the night shift as well as the early portion of the morning shift was most prone to impairment of work efficiency.     

The Shift-Work Accident Rate is More Related to the Shift Type than to Shift Rotation

The current study investigated the accident rates across morning, late, and night shifts in rotating shift-workers employed in two different shift rotations at the same steel work factory. A retrospective analysis has been performed of accident data (N = 578) over a 5-year period (2003 through 2007) of 730 male shift-workers employed in either a clockwise (mean age of the workers 38.1 ± SD 9.8 years) or counterclockwise rotation (mean age 38.0 ± SD 10.1 years) with comparable work conditions. The overall accident rate across the 24-h day was not significantly different between clockwise and counterclockwise shift rotation. In both shift-work rotations, morning shifts as opposed to night shifts exhibited a significantly higher accident rate. There was no significant difference between late shifts and morning or night shifts in either shift rotation. The increased accident rate in the morning shift at this steel factory could be related to the early starting time of the shift and to this shift being more labor intensive in both shift rotations. These findings suggest that work-related factors must be considered in addition to shift-work schedules when investigating accident rates in rotating shift-workers.     

The influences of sleep duration,chronotype, and nightwork on the ovarian cycle

ABSTRACT

Despite research indicating that sleep disorders influence reproductive health, the effects of sleep on reproductive hormone concentrations are poorly characterized. We prospectively followed 259 regularly menstruating women across one to two menstrual cycles (the BioCycle Study, 2005–2007), measuring fasting serum hormone concentrations up to eight times per cycle. Women provided information about daily sleep in diaries and chronotype and night/shift work on a baseline questionnaire. We evaluated percent differences in mean hormone concentrations, the magnitude of shifts in the timing and amplitude of hormone peaks, and the risk for sporadic anovulation associated with self-reported sleep patterns and night/shift work. We estimated chronotype scores – categorizing women below and above the interquartile range (IQR) as “morning” and “evening” chronotypes, respectively. For every hour increase in daily sleep duration, mean estradiol concentrations increased by 3.9% (95% confidence interval [CI] 2.0, 5.9%) and luteal phase progesterone by 9.4% (CI 4.0, 15.2%). Receiving less than 7 hours of sleep per day was associated with slightly earlier rises in peak levels for several hormones. Women reporting night/shift work (n = 77) had lower testosterone relative to women employed without night/shift work (percent difference: ?9.9%, CI ?18.4, ?0.4%). Women with morning chronotypes (n = 47) had earlier rises in estradiol during their cycles and potentially an earlier rise in luteinizing hormone. Compared to those who had intermediate chronotypes, women with evening chronotypes (n = 42) had a later luteinizing hormone peak of borderline statistical significance. A reduced risk for sporadic anovulation was suggested, but imprecise, for increasing hours of daily sleep leading up to ovulation (risk ratio 0.79, CI 0.59, 1.06), while an imprecise increased risk was observed for women with morning chronotypes (risk ratio 2.50, CI 0.93, 6.77). Sleep-related hormonal changes may not greatly alter ovarian function in healthy women, but have the potential to influence gynecologic health.     

Sleep Length as a Function of Morning Shift‐Start Time in Irregular Shift Schedules for Train Drivers: Self‐Rated Health and Individual Differences

Forty‐six male train drivers (mean age=46.5, SD=5.1) were recruited to participate in a diary study for 14 consecutive days with questions about their sleep and working hours. A polynomial mixed‐effect regression model showed a curvilinear relation (p <. 001) between shift‐start time and sleep duration for shifts starting at 03∶00–12∶00 h and with a near linear increase for ones starting between 04∶30 and 09∶00 h of approximately 0.7 h for every 1 h the shift was delayed. The longest sleeps were estimated at ～8 h before shifts that started at ～10∶00 h. The shortest sleeps were found for shifts that started before 04∶30 h and were estimated at ～5 h. Individual differences were estimated with a random-effect standard deviation of 0.51 h, independent of shift‐start time (p =.005). One‐half of the between‐subject variance was explained by subjective health. A one‐step decrease in health was associated with a 26 min increase in sleep length. The results have practical implications for constructing shift schedules. Early morning shifts reduced sleep length substantially and should be mixed with later start hours to avoid the accumulation of sleep dept. Delaying the shift‐start past 10∶00 h had little effect on sleep opportunity; however, delaying shift‐start to between 04∶30 and 9∶00 h had a strong impact on sleep length, with 70% of the extra time used for sleep, suggesting large positive effects for this range of shift‐start times.     

Sleep length as a function of morning shift-start time in irregular shift schedules for train drivers: self-rated health and individual differences

Forty-six male train drivers (mean age = 46.5, SD = 5.1) were recruited to participate in a diary study for 14 consecutive days with questions about their sleep and working hours. A polynomial mixed-effect regression model showed a curvilinear relation ( p < .001) between shift-start time and sleep duration for shifts starting at 03:00-12:00 hand with a near linear increase for ones starting between 04:30 and 09:00 h of approximately 0.7 h for every 1 h the shift was delayed. The longest sleeps were estimated at approximately 8 h before shifts that started at approximately 10:00 h. The shortest sleeps were found for shifts that started before 04:30 h and were estimated at approximately 5 h. Individual differences were estimated with a random-effect standard deviation of 0.51 h, independent of shift start time ( p = .005). One-half of the between-subject variance was explained by subjective health. A one-step decrease in health was associated with a 26 min increase in sleep length. The results have practical implications for constructing shift schedules. Early morning shifts reduced sleep length substantially and should be mixed with later start hours to avoid the accumulation of sleep dept. Delaying the shift-start past 10:00 h had little effect on sleep opportunity; however, delaying shift-start to between 04:30 and 9:00 h had a strong impact on sleep length, with 70% of the extra time used for sleep, suggesting large positive effects for this range of shift-start times.     

Effects of shift changes on female workers at a dish factory

This study investigated the effects of working night shifts on social and family life by examining changes in workers' daily life before and after a change in their shifts. Subjects were 40 women aged 27-59 years, working at a dish factory. During the health examination of night workers in autumn of 2000, the subjects were directly interviewed about changes in their lives induced by the shift change. Question parameters consisted of 8 items including 30 sub-items related to social and family life, such as sleep, rest, meals, sports, family time, hobbies, neighborhood association and social activities. The subjects selected one of four response categories: "becoming worse", "no change", "becoming better" and "difficult to determine." With regard to the percentage of "becoming worse", meal-related items ranked high in all of the shift types. "Family time" and "hobbies" showed high percentages in the subjects transferring from day shifts to night shifts, and in those transferring from early-morning shifts to night shifts. "Rest", "sports" and "hobbies" showed high percentages in the subjects transferring from night shifts to midnight shifts. Decreased sleeping hours were confirmed in all of the shift types, while the subjects tended to sleep more soundly. As the workers transfer to shifts at earlier hours, they were obliged to make sacrifices in various aspects of their social and family life. Therefore, much assistance in this regard should be given to them.     

Shift-specific associations between age,chronotype and sleep duration

The objective of this study was to examine the association of age with chronotype and sleep duration in day workers and rotating shift workers, including night shift work. Between October 2012 and February 2015, a cross-sectional study was conducted in a German chemical company. Using the “Munich ChronoType Questionnaire” (MCTQ), data about sleep onset and sleep offset during workdays and work-free days were retrieved and the chronotype was computed during regular voluntary occupational health check-ups. Associations between age and chronotype, as well as sleep duration, were assessed using linear regression analyses. Potential effect modification by the working time system was examined. Within the study period, 4,040 employees (82.3% and 17.7% were engaged in day work and rotating shift work, respectively) completed the questionnaire. Study participants were on average 41.8 years old (Min = 18.0, Max = 65.0, SD = 10.2) and predominantly male (75.4%). Mean chronotype and overall sleep duration was 03:22 (SD = 54 min) and 7.2 h (SD = 1.0 h) respectively. Older age was associated with earlier chronotype and reduced overall sleep duration in both day workers and rotating shift workers (p < 0.001 for all models). Compared to day workers, employees whom engaged in rotating shift work were later chronotypes and had overall a longer sleep duration. With older age, the difference between day and rotating shift workers regarding chronotype increased, while the difference regarding overall sleep duration decreased (p_interaction<0.005 for both models). This finding could indicate that both changes in circadian physiology and exposure to certain work schedules contribute to the age-related changes. Older rotating shift workers, with early chronotypes may have issues with night shifts, while day work and morning shifts may be best compatible to earlier chronotypes. Differences in sleep timing across age groups, might indicate that the same work hours will affect shift workers differently, dependent on their age, suggesting that more flexible and chronotype-adapted work hours could provide useful; especially for older employees. Sleep education in the form of courses and health campaigns could be a way to raise awareness of the importance of a healthy sleep pattern. This could be achieved by learning strategies to better adjust individual sleep patterns to work hours.     

Health Care Utilisation and Out-of-Pocket Expenditure Associated with Back Pain: A Nationally Representative Survey of Australian Women

Background

Back pain impacts on a significant proportion of the Australian population over the life course and has high prevalence rates among women, particularly in older age. Back pain care is characterised by multiple practitioner and self-prescribed treatment options, and the out-of-pocket costs associated with consultations and self-prescribed treatments have not been examined to date.

Objective

To analyse the extent of health care practitioner consultations and self-prescribed treatment for back pain care among Australian women, and to assess the self-reported costs associated with such usage.

Methods

Survey of 1,310 women (response rate 80.9%) who reported seeking help for back pain from the ‘1946-51 cohort’ of the Australian Longitudinal Study on Women’s Health. Women were asked about their use of health care practitioners and self-prescribed treatments for back pain and the costs associated with such usage.

Results

In the past year 76.4% consulted a complementary and alternative practitioner, 56% an allied health practitioner and 59.2% a GP/medical specialist. Overall, women consulted with, on average, 3.0 (SD = 2.0) different health care practitioners, and had, on average, 12.2 (SD = 9.7) discrete health care practitioner consultations for back pain. Average self-reported out-of-pocket expenditure on practitioners and self-prescribed treatments for back pain care per annum was AU$873.10.

Conclusions

Multiple provider usage for various but distinct purposes (i.e. pain/mobility versus anxiety/stress) points to the need for further research into patient motivations and experiences of back pain care in order to improve and enhance access to and continuity of care. Our results suggest that the cost of back pain care represents a significant burden, and may ultimately limit women’s access to multiple providers. We extrapolate that for Australian working-age women, total out-of-pocket expenditure on back pain care per annum is in excess of AU$1.4billion, thus indicating the prominence of back pain as a major economic, social and health burden.     

Influence of Flexibility and Variability of Working Hours on Health and Well‐Being

Flexible working hours can have several meanings and can be arranged in a number of ways to suit the worker and/or employer. Two aspects of “flexible” arrangement of working hours were considered: one more subjected to company control and decision (variability) and one more connected to individual discretion and autonomy (flexibility). The aim of the study was to analyze these two dimensions in relation to health and well‐being, taking into consideration the interaction with some relevant background variables related to demographics plus working and social conditions. The dataset of the Third European Survey on working conditions, conducted in 2000 and involving 21,505 workers, was used. Nineteen health disorders and four psycho‐social conditions were tested by means of multiple logistic regression analysis, in which mutually adjusted odds ratios were calculated for age, gender, marital status, number of children, occupation, mode of employment, shift work, night work, time pressure, mental and physical workload, job satisfaction, and participation in work organization. The flexibility and variability of working hours appeared inversely related to health and psycho‐social well‐being: the most favorable effects were associated with higher flexibility and lower variability. The analysis of the interactions with the twelve intervening variables showed that physical work, age, and flexibility are the three most important factors affecting health and well‐being. Flexibility resulted as the most important factor to influence work satisfaction; the second to affect family and social commitment and the ability to do the same job when 60 years old, as well as trauma, overall fatigue, irritability, and headache; and the third to influence heart disease, stomachache, anxiety, injury, and the feeling that health being at risk because of work. Variability was the third most important factor influencing family and social commitments. Moreover, shift and night work confirmed to have a significant influence on sleep, digestive and cardiovascular troubles, as well and health and safety at work. Time pressure also showed a relevant influence, both on individual stress and social life. Therefore, suitable arrangements of flexible working time, aimed at supporting workers' coping strategies, appear to have a clear beneficial effect on worker health and well‐being, with positive consequences also at the company and social level, as evidenced by the higher “feeling to be able to work until 60 years of age”.     

Influence of flexibility and variability of working hours on health and well-being

Flexible working hours can have several meanings and can be arranged in a number of ways to suit the worker and/or employer. Two aspects of “flexible” arrangement of working hours were considered: one more subjected to company control and decision (variability) and one more connected to individual discretion and autonomy (flexibility). The aim of the study was to analyze these two dimensions in relation to health and well-being, taking into consideration the interaction with some relevant background variables related to demographics plus working and social conditions. The dataset of the Third European Survey on working conditions, conducted in 2000 and involving 21,505 workers, was used. Nineteen health disorders and four psycho-social conditions were tested by means of multiple logistic regression analysis, in which mutually adjusted odds ratios were calculated for age, gender, marital status, number of children, occupation, mode of employment, shift work, night work, time pressure, mental and physical workload, job satisfaction, and participation in work organization. The flexibility and variability of working hours appeared inversely related to health and psycho-social well-being: the most favorable effects were associated with higher flexibility and lower variability. The analysis of the interactions with the twelve intervening variables showed that physical work, age, and flexibility are the three most important factors affecting health and well-being. Flexibility resulted as the most important factor to influence work satisfaction; the second to affect family and social commitment and the ability to do the same job when 60 years old, as well as trauma, overall fatigue, irritability, and headache; and the third to influence heart disease, stomachache, anxiety, injury, and the feeling that health being at risk because of work. Variability was the third most important factor influencing family and social commitments. Moreover, shift and night work confirmed to have a significant influence on sleep, digestive and cardiovascular troubles, as well and health and safety at work. Time pressure also showed a relevant influence, both on individual stress and social life. Therefore, suitable arrangements of flexible working time, aimed at supporting workers' coping strategies, appear to have a clear beneficial effect on worker health and well-being, with positive consequences also at the company and social level, as evidenced by the higher “feeling to be able to work until 60 years of age”.     

The Relation between Occupational Sitting and Mental,Cardiometabolic, and Musculoskeletal Health over a Period of 15 Years – The Doetinchem Cohort Study

Objective

Sedentary behaviors are reported to impose health risks. Since occupational exposure is a major proportion of total sedentary time, we studied the association between occupational sitting and a number of health problems.

Methods

From the longitudinal Doetinchem Cohort Study, we selected those working at baseline with complete data (n = 1,509). Participants were examined four times at 5 year-intervals between 1993 and 2012. We characterized occupational sitting as follows: 1) stable sitters and stable non sitters over a 15-year period, based on job characteristics and (2) having a job with a low, moderate or high amount of sitting, based on tertiles of self-reported number of hours per week of occupational sitting, measured at wave 5. Linear and logistic regression models were used. Outcomes were self-reported mental health, low-back or upper extremity pain, and objectively measured cardiometabolic health (overweight, hypertension, hypercholesterolemia).

Results

Compared to stable non sitters, a lower risk of chronic upper extremity pain was observed for stable sitters (OR 0.75, 95% CI: 0.57; 1.00) as well as for those in the two upper tertiles for hours of occupational sitting (>4 hr/wk) (OR 0.65; 95%CI 0.50–0.86). For the other health outcomes studied, no significant associations were found with occupational sitting.

Conclusion

Our findings do not support the hypothesis that occupational sitting is associated with health problems. The finding that occupational sitting is associated with less upper extremity pain might be due to the association of occupational sitting with less physical load.     

Increased Insomnia Symptoms Predict the Onset of Back Pain among Employed Adults

Background

Back pain is among the most prevalent pain disorders causing chronic disability among adults, and insomnia is a common co-morbidity. However, whether insomnia precedes back pain or vice versa remains unclear. The current study tested the temporal association between insomnia and back pain.

Methods

A longitudinal design was used to investigate whether changes in insomnia over time predict the onset of back pain and vice versa. The study was conducted on a cohort of active healthy working adults (N = 2,131, 34% women) at three time points (T1, T2, and T3) over a period of 3.7 years (range = 2.2–5.12) years. Logistic regression analysis was used to test whether increased insomnia symptoms from T1 to T2 predicted the onset of new back pain. Ordinary least squares regression was used to test whether the existence of back pain at T2 predicted an increase in insomnia from T2 to T3.

Results

The results indicated that after controlling for socioeconomic variables, self-reported health, lifestyle behaviors, and anthropometrics, a T1–T2 increase in insomnia symptoms was associated with a 1.40-fold increased risk of back pain at T3 (OR = 1.40; 95% CI = 1.10–1.71). No support was found for reverse causation; i.e., that back pain predicts subsequent increase in insomnia.

Conclusions

Insomnia appears to be a risk factor in the development of back pain in healthy individuals. However, no evidence of reverse causation was found.     

Musculoskeletal complaints among Italian X-ray technology students: a cross-sectional questionnaire survey

Background

There is a high prevalence of musculoskeletal disorders among healthcare professional students. Although recent studies show musculoskeletal disorders are a common problem among X-ray technologists, there are no data on these disorders among students of this healthcare profession. We have therefore estimated the prevalence of musculoskeletal complaints among a group of X-ray technology students.

Methods

The students (n = 109) currently attending the 3-year X-ray technologist school at a large University in the Apulia region of Southern Italy were recruited for the study, with a 100% participation rate. A questionnaire collected data concerning personal characteristics, physical exposure during training activities, and the presence of musculoskeletal symptoms in the neck, shoulders, low back, hand/wrist and legs.

Results

The prevalence of complaints in any body site over the previous 12 months was 37%. Low back pain was the most frequently reported symptom (27%), followed by neck (16%), shoulder (11%), leg (8%) and hand/wrist (5%) pain. Poor physical activity was associated with the complaints.

Conclusions

Our study showed prevalence rates of musculoskeletal complaints among X-ray technology students to be somewhat high, representing about half of those found in Italian technologists. The most common musculoskeletal problem was low back pain, which had also been found in research conducted among nursing students. Our research also showed a significant association between poor physical activity and the presence of musculoskeletal disorders in young university students.

     

Effects of Work and Orcadian Rhythm on Bus Drivers' Oral Temperature

The results described in this paper originate from a research project aiming at the development of a useful measuring instrument which can demonstrate the effect of work and work circumstances on the task performer. Among other physiological (and psychometric) variables, oral temperature data were obtained from eight younger and eight older bus drivers working in various shifts. Measurements were performed in an experimental design under standardized conditions in a mobile laboratory before starting, during some rest intervals, and after finishing work. The same measurements were performed on the bus drivers in a control condition at corresponding times on a day off. The results indicated that only during the working days a temperature pattern could be detected resembling the data found in the literature (low in the morning, a maximum in the late afternoon, then a decline). No clear pattern was discernible on work-free days. On working days the mean oral temperature values were significantly higher at corresponding hours of the day. Upward deviations of the temperature pattern were found before starting work (but also at the beginning of the day off), while lower values were obtained after finishing work (especially in the shifts starting in the morning). These results might be interpreted in terms of interaction between circadian rhythm and activating and de-activating tendencies connected with (structured) daily activities.     

Effects of Work and Orcadian Rhythm on Bus Drivers' Oral Temperature

The results described in this paper originate from a research project aiming at the development of a useful measuring instrument which can demonstrate the effect of work and work circumstances on the task performer. Among other physiological (and psychometric) variables, oral temperature data were obtained from eight younger and eight older bus drivers working in various shifts. Measurements were performed in an experimental design under standardized conditions in a mobile laboratory before starting, during some rest intervals, and after finishing work. The same measurements were performed on the bus drivers in a control condition at corresponding times on a day off. The results indicated that only during the working days a temperature pattern could be detected resembling the data found in the literature (low in the morning, a maximum in the late afternoon, then a decline). No clear pattern was discernible on work-free days. On working days the mean oral temperature values were significantly higher at corresponding hours of the day. Upward deviations of the temperature pattern were found before starting work (but also at the beginning of the day off), while lower values were obtained after finishing work (especially in the shifts starting in the morning). These results might be interpreted in terms of interaction between circadian rhythm and activating and de-activating tendencies connected with (structured) daily activities.     

The Relation of Shift Work Tolerance to the Circadian Adjustment

The amplitude and phasing of circadian rhythms are under discussion as possible predictors of tolerance to night work. In a field study, subjective sleepiness and oral temperature of 147 female nurses were measured at 2-hour intervals during a period with one morning shift and two consecutive night shifts. The nurses also filled out a questionnaire. Two types of tolerance indices were constructed: The “health index” was based on questions referring to general fatigue, gastrointestinal symptoms, and sleep disturbances, and the “sleepiness index” on the actual subjective ratings of sleepiness. According to the health index, the group with good tolerance had a larger circadian amplitude of the oral temperature rhythm on the day of the morning shift than the group with poor tolerance. However, with regard to the sleepiness index, the corresponding difference between the groups with good or poor tolerance was not significant. The data did not confirm the hypothesis that predicts a quick adjustment of the circadian rhythm when the circadian amplitude is small before the change to night work. The contradictory results found in this and in other studies do not yet permit prediction of tolerance to night work.     

Can Melatonin Improve Shift Workers' Tolerance of the Night Shift? Some Preliminary Findings

The pineal hormone melatonin is potentially useful in the treatment of disorders, especially sleep disorders, associated with circadian rhythm disturbance. We have examined its effects on sleep, mood, and behaviour in a double-blind, placebo-controlled study of a small group of police officers working spans of seven successive night shifts. Compared to placebo, and to no treatment, melatonin (5 mg) taken at the desired bedtime improved problems related to sleep and increased alertness during working hours, especially during the early morning. In letter-target performance tests visual search speed and accuracy were either unchanged or slightly improved. Memory scanning speed and perception of mental load were adversely affected. This preliminary study suggests that melatonin has beneficial effects on sleep and alertness, but that its effects on performance need careful evaluation.     

Can Melatonin Improve Shift Workers' Tolerance of the Night Shift? Some Preliminary Findings

The pineal hormone melatonin is potentially useful in the treatment of disorders, especially sleep disorders, associated with circadian rhythm disturbance. We have examined its effects on sleep, mood, and behaviour in a double-blind, placebo-controlled study of a small group of police officers working spans of seven successive night shifts. Compared to placebo, and to no treatment, melatonin (5 mg) taken at the desired bedtime improved problems related to sleep and increased alertness during working hours, especially during the early morning. In letter-target performance tests visual search speed and accuracy were either unchanged or slightly improved. Memory scanning speed and perception of mental load were adversely affected. This preliminary study suggests that melatonin has beneficial effects on sleep and alertness, but that its effects on performance need careful evaluation.