Daytime napping and its effects on alertness and short-term memory performance in shiftworkers

Summary Daytime napping and its effects on 145 female shiftworkers were studied by comparing the individual characteristics, alertness, and short-term memory performance of subjects who took or did not take naps. Of the subjects 56% (n = 82) took a nap before a night shift and 21% (n = 30) after a morning shift. After a morning shift, napping was more frequent among evening types and subjects living alone (not married). Before a night shift, daytime napping was not connected to individual characteristics, but the total sleep time of nappers during the preceding night was shorter than that of non-nappers. At 10.00 and at 04.00–08.00, at the end of the night shift, nappers were significantly more alert than subjects who had not taken naps. The length and timing of the daytime nap did not correlate to either alertness or performance during the following night. In a questionnaire, nappers before a night shift had less sleep disturbances than non-nappers.     

The nighttime nap strategies for improving night shift work in workplace

Nighttime napping is an effective measure to prevent adverse effects due to night shift work. A characteristic of nighttime nap is that it can result in considerably deeper sleep. Several studies have shown that taking nighttime naps suppressed increasing sleepiness, decreasing alertness during the period following awaking from a nap, and prevented disturbance of circadian rhythm ("anchor sleep"). The length of daytime sleep after night shift, when combined with a nighttime nap, is shorter than that without nap. This finding might be interpreted as a beneficial effect rather than a negative feature because workers can then spend time engaged in other activities rather than sleeping. Nevertheless, the introduction of nighttime sleep break in the workplace has not been widely accepted. To promote nighttime napping strategy in the workplace, consensus building while acting on conflicting interest is essential. Recently, participatory method for improvement of working condition has expanded worldwide. A characteristic of the activity is using action checklist and group work, and heightening motivation to improvement working condition between worker and manager. Through the activities, nighttime napping strategy would be spread more in the workplaces and play a role as one of the effective tools for improving working conditions, work performance and safety in the future.     

Effects of Two 15-min Naps on the Subjective Sleepiness,Fatigue and Heart Rate Variability of Night Shift Nurses

The purpose of this study was to examine the effects of two 15-min naps on nurses who work at night in a three-shift system. Of the 15 nurses who were included as study subjects on a night shift, eight took two short naps (the Nap condition), and seven worked without taking a nap (the No-nap condition) during the night shift. We measured sublingual temperature and the bispectral index (BIS), obtained heart rate and heart rate variability measures from an electrocardiogram (ECG), and evaluated sleepiness and fatigue levels every hour using the Visual Analog Scale (VAS). Both subjective sleepiness and fatigue increased between 4:00 and 5:00, with no significant differences observed between the two groups. However, the low- to high-frequency ratio (LF/HF) in the Nap condition group was found to be significantly lower than in the No-nap condition group. Furthermore, a sudden, brief increase in HF values was observed in the No-nap condition group in the morning. The results of this study suggest that taking two short naps may effectively reduce tension and prevent a brief increase in HF values by suppressing sympathetic nervous activity in the morning.     

Effects of 2-hour nighttime nap on melatonin concentration and alertness during 12-hour simulated night work

A nighttime nap is expected to mitigate melatonin suppression during night work by blocking light input to the retina, but it is unclear. In the present study, we investigated the effects of a nap break on melatonin level, subjective sleepiness, and vigilance performance during simulated night work. Eleven healthy young males (mean ± SD age: 22.2 ± 4.1 years) participated in counterbalanced crossover design experiments with two conditions (nap vs. no nap). The subjects performed 12-hour simulated night work from 21:00 to 09:00 h (illuminance: ∼500 lx). Subjects with a nap condition took a nap for 2 hours in a dark room from 03:00, while subjects with a no nap condition continued the simulated night work. The results showed that immediately after the 2-h nap break, the melatonin level at 05:00 h temporarily recovered from light-induced melatonin suppression during the simulated night work but significantly suppressed again at 07:00 and 09:00 h. Subjective alertness and vigilance performance were impaired immediately after the nap break but subsequently enhanced. The results suggest that a single nap break for 2 hours could be a strategy to enhance alertness during the last part of night shift but inadequate for mitigating melatonin suppression.     

孕前午睡与目前夜眠时长对孕晚期疲劳的相关性研究

目的 讨论孕前午睡与目前夜眠时长对孕晚期正常孕妇疲劳程度的影响.方法 收集2020年1～12月于厦门大学医学院第二附属医院就诊的正常孕晚期(孕28周～分娩)孕妇490例,收集其一般人口学信息与临床资料,记录孕前午睡与目前夜眠有效睡眠时长,排除3例缺失夜眠时长样本,有效样本487例.按孕前是否午睡分为午睡(n=332)和...     

Effects of consecutive night shifts with prolonged on-duty and overtime work on various sleep

The purpose of this research was to investigate the effect of consecutive night shifts upon various types of sleep. The subjects studied were 9 guards who usually worked on an alternate-day shift system. The nighttime nap EEG (3:00-6:30) during the 24-hr on-duty period was recorded, and then the subsequent day sleep EEG (11:00 to spontaneous awakening) and recovery night sleep (23:00 to spontaneous awakening) were also measured. These records were made for the nap, day sleep and recovery night under two different sets of conditions. The first was for the usual shift cycle (U), i.e. 24 hr duty (10:00-10:00)----off duty----24 hr duty----off duty. The other was for consecutive night shifts (CN) with overtime work (18:00-10:00) performed on the normal off day, i.e. 24 hr duty----8 hr off duty----40 hr duty----off duty. The results were as follows: There was no difference between U and CN conditions concerning time in bed and total sleep time in the nighttime nap, day sleep and recovery night. However, the total time of daytime sleep was significantly shortened under both U and CN conditions, as compared with the control night. The amount of REM sleep in the CN condition for both the nighttime nap and day sleep was significantly greater than in the U condition. In the recovery night, REM sleep continued to be slightly greater for the CN condition than for the U condition. Slow wave sleep (SWS) in the CN condition was slightly greater than in the U condition for the nighttime nap and day sleep, but in the recovery night, no difference was observed between the two conditions. In the U condition, the sleep onset REM period (SOREMP) was observed in 2 of the 9 cases, but only during the day sleep. In the CN condition, however, it occurred in 5 subjects during the nighttime nap, in 4 during the day sleep, and in 2 during the recovery night. The REM sleep latency in the CN condition thus tended to be diminished in each type of sleep compared with that in the U condition, but a significant difference between the two conditions was observed only in the nighttime nap. It is believed that the increase in the amount of REM sleep and in the frequency of SOREMP might be due to the repeated pattern of sleep loss and shortened periods of sleep during consecutive night shifts of prolonged duty, with partial sleep deprivation resulting from lack of REM sleep.     

An occupational health physician's report on the improvement in the sleeping conditions of night shift workers

This paper reviews briefly our research findings on sleep and health for shift workers at a bakery and a dish factory and aims to give some information on health protection with improved sleep. Our medical examinations revealed that rises in blood pressure (BP) were frequently observed in male bakery workers on the fixed night shift. They took a two-hour nap from 1:00 to 3:00 during the night shifts according to our advice. As a result, their diastolic BP significantly decreased in subsequent years. Women working shifts before 3:00 at a dish factory seemed to show more sleep disturbance, higher daytime sleepiness, and more fatigue than those working shits from 3:00. Total sleep hours taken during the daytime was similar between two groups. Among the dish, factory workers who switched to midnight or night shifts, 70% reported slow recovery from fatigue and 30% felt deteriorated health. These women also reported increased efforts to obtain a deep sleep, probably making up for shortened sleep. Occupational physicians can act to improve shift work conditions through monitoring the health of workers, applying naps, and designing possible schedules to secure deep, sufficient sleep.     

Sleepiness and road accidents among policemen on shif-work on Italian highways: study of the national highway network in the period of 1993-1997

Sleep disorders and daytime sleepiness are the most frequent disturbances reported by shift-workers. Sleepiness and fatigue can increase the risk of human errors and accidents especially during night work. In order to evaluate the time distribution and the possible role of sleepiness on road accidents in policemen on shift-work on highway patrols over 24 hours, we analyzed 1218 car accidents that occurred on the Italian highway network in the period 1993-1997. Accidents occurring during day shifts were significantly correlated with traffic density while accidents occurring during night shifts were not. During the 19:00-01:00 h shift the number of accidents showed a progressively increasing trend with two significant peaks around 23:00 and 01:00 h. Accidents occurring during the 01:00-07:00 h shift did not show significant trends. Information about sleep habits before starting night shifts were obtained by means of telephone interviews. While 85% of the subjects usually took a nap (30-90 min) before the 01:00-07:00 h shift only 15% took a short nap (< 30 minutes) before the 19:00-01:00 h shift. The data can be interpreted as a balance between circadian factors, homeostasis and fatigue related influences and spontaneously adopted counteracting strategies to increase the level of vigilance during night work hours. While a long nap seems to reduce the risk of accidents during the 01:00-07:00 h shift, policemen seem to underestimate the risk of sleepiness during the shift 19:00-01:00 h shift.     

Sleep strategies of 12-hour shift nurses with emphasis on night sleep episodes

OBJECTIVES: Episodes of sleep during a nightshift are frequently reported in various types of jobs. This phenomenon has been seldom documented so far. This field study investigated individual differences in the sleep-wake behavior of nurses. METHODS: A group of eight nurses working in an intensive care unit on a two 12-hour shift system kept a "sleep diary" for 1 month, recording main sleep periods and naps. They subjectively assessed sleepiness, sleep quality, and the need for sleep at various times of the day and night. Continuous actimetric measurements provided an evaluation of the rest-activity patterns and of the sleep parameters. RESULTS: Half of the nurses chose to take naps in 75% of their nightshifts. No differences between the night-nappers and nonnight-nappers were found for either total sleep length or the temporal patterns of subjective sleepiness at night but, during nightwork, night-nappers needed sleep earlier than nonnight-nappers. They had long naps during a worknight and short daytime sleep, sometimes followed by a late afternoon nap. This strategy probably favored the maintenance of a diurnal orientation. Nonnight-nappers had long daytime sleep and took preventive naps to anticipate sleepiness during nightwork. However, their readjustment to diurnal life seemed more difficult than that of night-nappers. CONCLUSIONS: Nurses use different sleep-wake strategies to cope with nightwork. These different strategies may be due to circadian influence although social factors cannot be totally excluded.     

Penile tumescence monitoring during morning naps to assess male erectile functioning: An initial study of healthy men of varied ages

Whether sleep erections occurred during morning naps (preceded by modest sleep deprivation) in healthy men whose ages were representative of clients in sexual health clinics was assessed. Subjects (N = 30) reduced their normal sleep time to increase the likelihood that they would experience rapid eye movement (REM) sleep [closely associated with nocturnal penile tumescence (NPT)]. They then reported to an outpatient psychophysiological laboratory for an early morning nap, during which sleep and penile tumescence measures were recorded continuously. All subjects were able to sleep during at least 1 of their 2 recording sessions, 24 (80%) experienced REM sleep, and 22 (73%) experienced tumescence episodes consistent with previous NPT studies. The magnitude of these erections could reduce concerns about the presence of organic pathology, and obviate the need for an NPT study. Results suggest that monitoring tumescence during naps may be useful as an inexpensive and convenient screening approach in the assessment of male erectile functioning.Supported in part by grants from Syracuse University to Christopher M. Gordon, and from the National Institute of Mental Health Grant 1-K21-MH01101 to Michael P. Carey.     

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

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

Actual conditions of work, fatigue and sleep in non-employed, home-based female information technology workers with preschool children

We conducted a study on time budget and fatigue feelings over a two-month period of 12 non-employed, home-based female workers using computers (mean age 35.2 yr). All of them had at least one preschool child. The actual amount of work done by these women and the related effects on the fatigue feelings and sleep were investigated. The results showed that the work done was characterized by involving many night hours, irrespective of the day of the week. The degree of subjective fatigue was not dependent on the number of hours worked, but affected by the time at which the work of the day was completed. This tendency was notable after one o'clock in the morning when the work was completed. Those who followed such a work pattern took daytime naps, although a quality of the subsequent nighttime sleep taken might be poor. They took a nap around 14:00 but not around 19:00. The sleep strategies were thus shown to be affected by home-based work. A need is suggested to support these workers in adjusting work time distribution and taking sleep patterns adapted to individual conditions.     

Sleepiness in various shift combinations of irregular shift systems

The present study examined the occurrence of sleepiness in various shift combinations ending with a night or morning shift. Three weeks' sleep/work shift diary data, collected from 126 randomly selected train drivers and 104 traffic controllers, were used in statistical analyses. The occurrence of sleepiness at work (i.e., Karolinska Sleepiness Scale 7 or higher) was tested with a generalised linear model with repeated measurements including explanatory factors related to shifts, sleep, and individual characteristics. The prevalence of severe sleepiness varied between 25% and 62% in the combinations ending with a night shift and between 12% and 27% in the combinations ending with a morning shift. The occurrence of sleepiness did not, however, systematically vary between the shift combinations in either case. An increased risk for sleepiness was associated with high sleep need and long shift duration in the night shift and with high sleep need, short main sleep period, long shift duration and an early shift starting time in the morning shift. Also having a child was associated with an increased risk for sleepiness in the night shift. The results suggest that the shift history of 24-36 h prior to the night and the morning shift is not strongly associated with the occurrence of sleepiness at work, but there are other factors, such as shift length and starting time and sleep need, that affect a risk for sleepiness at work.     

Changes in melatonin and sex steroid hormone production among men as a result of rotating night shift work – the HORMONIT study

ObjectiveData from real world settings on circadian disruption and subsequent hormone-related changes may explain the higher risk of hormone-dependent cancers among night shift workers.The present study examines the melatonin and sex steroid hormone levels among night shift workers.MethodsWe included 44 male, rotating shift workers from a car factory in Spain, sampled both at the end of a 3-week night shift (22:00–06:00 hrs) and a 3-week early morning shift (06:00–14:00 hrs). Participants collected all urine voids over 24-hours during each shift. Urinary concentrations of sex steroid hormones (estrogens, androgens and progestogens) and 6-sulfatoxymelatonin (aMT6s, major melatonin metabolite) were determined. Individual cosinor analysis was used to derive the acrophase (peak time) and area under the curve (total production). Linear mixed models examined intraindividual associations between night shift work and log-transformed 24-hour peak time and total production of hormones compared to early morning shift work.ResultsThe acrophase was delayed during the night shift for aMT6s [geometric mean difference (GMD) 7.53 hrs, 95% confidence interval (CI) 4.46–10.60], androgens (eg, testosterone: GMD 6.83 hrs, 95% CI 0.34–13.32) and progestogens (eg, 17-hydroxyprogesterone: GMD 4.54 hrs, 95% CI 2.92–6.16) compared to the early morning shift. We found a higher production of adrenal androgen 11-oxoandrosterone/11-oxoetiocholanolone [geometric mean ratio (GMR) 1.43, 95% CI 1.12–1.81], and a lower production of adrenal progestogen 16-cysteinylprogesterone (GMR 0.79, 95% CI 0.67–0.93) during the night shift compared to the early morning shift levels.ConclusionsNight shift work was associated with melatonin and sex hormone-related changes in timing and total production, providing insight into the mechanistic path for its association with hormone-dependent cancer.     

A short nap and natural bright light exposure improve positive mood status

While the effects of a short nap on performance and arousal level have been well investigated, less attention has been paid to its effects on mood status. The aim of the present study was to examine the effects of a short nap and natural bright light exposure on mood status. Participants were 16 healthy females who were on average 38.1 (SD = 2.68) yr old. From 11:00 to 12:00, the participants carried out a set of tasks twice with baseline lighting (<100 lux). From 12:40 to 13:10, they were subjected to three experimental conditions: control (<100 lux), natural bright light (>2,000 lux), and a 20-min nap. From 13:10 to 16:10, the tasks were repeated six times with the baseline lighting. To measure mood status, multiple visual analogue scales (to measure anxiety, sadness, anger, confusion, apathy, fatigue, and sleepiness) and the Mood Check List 3 (MCL-3) (to derive "pleasantness", "satisfaction" and "relaxation") were employed. The results showed that brief (30 min) natural bright light exposure improved one dimension of mood status, "pleasantness". A short nap also improved dimensions of mood status ("pleasantness", "satisfaction", and "relaxation"). These results suggest that the proper application of both natural light and a short nap shifts the mood status to the positive/favorable side.     

Modifying effects of perceived adaptation to shift work on health, wellbeing, and alertness on the job among nuclear power plant operators

This study examined the relationship between perceived adaptation to shift work and shift-related problems. A total of 608 male operators at nuclear power plants completed a set of validated questionnaires including a modified version of the Standard Shiftwork Index, which covered adaptation to shift work, fit to job content, chronotypes, chronic fatigue, sleep, naps, shift work locus of control (SHLOC), psychological health, social/family life, daytime sleepiness, workload, alertness on the job, and lifestyle factors. Participants were divided into two groups according to their perceived level of adaptation to shift work. The good adaptation group showed better outcomes than the poor adaptation group in terms of fit to job content, chronic fatigue, daytime sleep before night shifts, social and family disruption, SHLOC, psychological health, and alertness during night shifts (ps<0.001). Operators who reported good adaptation also took a more frequent, longer nap and more cigarettes during night shifts (ps<0.05). The cross-sectional study design cannot determine a causal relationship between perceived adaptation and shift work problems, yet the present results suggest that the effects of working shifts may be modified by perceptions of shift work adaptation.     

Job demands and resting and napping opportunities for nurses during night shifts: impact on sleepiness and self-evaluated quality of healthcare

The aim of this field study is to describe night shift resting and napping strategies and to examine their beneficial effects on sleepiness and quality of work. The study was carried out with 16 nurses working in an intensive care unit. Data collected during 20 night shifts were related to job demands (systematic observations), to the duration and timing of rests and naps taken by nurses (systematic observations, sleep diaries), to sleepiness (Karolinska Sleepiness Scale), and to quality of work scores (visual analog scale). The results showed that the number of rests and naps depended on the job demands. Resting and napping lowered the levels of sleepiness at the end of the shift. There was no direct relationship between sleepiness and the quality of work score. Discussions about the choice of indicators for the quality of work are necessary. Suggestions for implementing regulations for prescribed napping during night shifts are presented.     

Rescheduling a three shift system at a steel rolling mill: effects of a one hour delay of shift starting times on sleep and alertness in younger and older workers.

OBJECTIVE: To evaluate a new work schedule at a Finnish steel mill with special attention to effects on older workers. The schedule was designed to improve sleep before the morning shift, and alertness during the morning shift, by delaying shift start and end times. METHODS: Evaluation was by a shiftwork health and safety questionnaire, recordings of work-rest-sleep cycles with activity monitors worn on the wrist, daily diaries, and on site computerised testing of fatigue and alertness by the NIOSH fatigue test battery. RESULTS: The one hour delay in shift starting times improved sleep before the morning shift, and improved waking fatigue, sleepiness, and performance during the morning shift. Evening and night shift sleep and fatigue or sleepiness, however, were affected negatively by the new work schedule, but the results for those shifts were less consistent across the various measures. Despite the improvements, most workers were not satisfied with the new schedule because of social concerns. Few interactions of age with the new work schedule were found, suggesting that the effects of the work schedule were uniform across age groups. CONCLUSION: A change of as little as one hour in shift starting times can improve morning shift sleep and alertness, but there are trade offs from these improvements in terms of night shift effects and social considerations. It seems, then, that optimal shift start and end times for an entire organisation are difficult to institute on a wide scale. Tailoring shift schedules to subgroups within an organisation is suggested.     

The sleep of Africans and Europeans in the Ivory Coast: questionnaire study

Sleep behaviour has been extensively studied with questionnaires in industrialised countries to investigate the epidemiology of sleep-wake disorders. However, only few attempts have yet been made to examine sleep behaviour of people living in Africa. Although, a large number of studies in hot or cold environments have used short-term exposures, reporting disrupted sleep for most of them, long-term exposures to stressful thermal environments are rare in the literature. Prior to the present investigation, we used questionnaires to analyse the effects of seasonal heat increase on perceived sleep behaviour and sleep quality in young native African students in Niger [7], even though these methods of investigation are by no means as accurate as polysomnographic recordings. The hypothesis was that sleep behaviour may be influenced by climatic variations in a hot dry tropical climate. Such climatic variations have been shown to induce seasonal heat acclimatisation marked by changes in body temperature rhythms in the hot versus the cool season [13]. Sleep behaviour was examined during two 7-day periods in January ("cool-dry" season, 88 subjects) and May ("hot-dry" season, 53 subjects). The questionnaire was completed after night sleep and/or naps. The subjects slept an average of 7 1/2 hours a day, most of them having afternoon naps. They experienced no major seasonal variation in their sleep behaviour, but for an increased number of awakenings during the hot season. Restorative quality of sleep scored lower after a nap than after nocturnal sleep. Therefore, general sleep characteristics were not modified by seasonal temperature variations in African native students, perhaps because of the limited changes in daylight under the low latitude of Niamey. Another investigation was carried out using the same 12-item questionnaire in Abidjan on 78 medical students who did not have a nap [9]. Contrary to the Niamey students, the Abidjan subjects adopted short duration sleep schedules, without any effect on the subjective quality of the restorative properties of their sleep.     

Work-shift period and weight change

The present study was done to determine whether weight gain was more prevalent in workers on late shifts than in those on day shifts. A questionnaire about changes in weight, food intake, exercise, and sleep since starting the job on the current shift was given to day-shift and late-shift (evening and night) hospital workers. Data were analyzed for 85 subjects, 36 of whom worked during the day shift and 49 the late shift. The late-shift group reported a mean weight gain of 4.3 kg, which was greater than the mean weight gain of 0.9 kg for the day-shift group (P = 0.02). There were, however, no significant differences in current body mass index (26.7 +/- 5.4 SD) between groups. There was a trend for late-shift workers to report eating more since beginning the later shift (P = 0.06). When combined with those reporting exercising less (P = NS), this trend became significant (P = 0.04). Late-shift workers reported eating fewer meals (1.9 +/- 0.9 SD) than the day-shift workers (2.5 +/- 0.9; P = 0.002). In addition, late-shift workers reported eating the last daily meal later (mean = 22:27, or 10:27 PM) than day-shift workers (17:52 or 5:52 PM; P < 0.00005). Late-shift workers also reported more naps (P = 0.01) and longer naps (P = 0.05) during the work week than did day-shift workers. The reported changes in eating, exercise, and sleep may contribute to the increased weight gain of late-shift workers.