Quantitative and qualitative aspects of sleep in young self-selected four-shift workers

Summary For 4 of 5 weeks, 27 shift workers daily registered the times they went to sleep and awoke and sleep difficulties. The subjects are employed in a semi-continuous four-shift system. A complete cycle comprises: six morning, six afternoon, and six night shifts, and six free days. Sunday is always free.The mean duration of sleep per 24 h over the 4 weeks is 8 h. The amount of sleep is significantly larger during the free week (8 h 18 min) and significantly smaller during the night shift week (7 h 26 min), when compared to the amounts of sleep in each of the other 3 weeks. Difficulties in getting to sleep and sleep interruptions are more common during day-sleep in the nightshift. Subtracting some time for every sleep interruption does not noticeably change the sleep duration data yielded for the night shift.These results suggest that the duration and quality of sleep of these shiftworkers living in a rural region is quite satisfactory. This can perhaps be explained by the time schedules used in this shift system, by compensation for relative lack of sleep made possible by the free week, by some (self-)selection of the workers, and finally by their young age.     

Effects of shift work on 24-hour ambulatory blood pressure and its variability among Japanese workers

OBJECTIVES: This study examined the effects of rotating shift work on blood pressure in a comparison of ambulatory blood pressure and long-term changes in blood pressure between shift and day workers. METHODS: Ambulatory blood pressure was measured for 24-hour periods at an interval of 30 minutes for 27 shift workers and 26 day workers when they worked during the day. Blood pressure was compared between these 2 groups of workers for 4 time categories (awake, sleep, nonwork awake, and work periods). Their long-term blood pressures, recorded in annual surveys, were reviewed for long-term changes. These comparisons were adjusted for the effects of body mass index, alcohol intake, anger expression, and physical activity. RESULTS: On the average, sleep time was shorter and the anger-in (ie, anger suppressed) score was higher for the shift workers than for the day workers, but body mass index and alcohol intake did not differ between the 2 groups. Even after adjustment for these co-variables, the mean systolic blood pressure during the 24-hour, awake, and work periods were higher among the shift workers than among the day workers. The 24-hour standard deviations of the systolic blood pressures were also higher for the shift workers than for the day workers. Among the shift workers, but not among the day workers, a significant long-term increase was observed in systolic blood pressure measured in the annual surveys. CONCLUSIONS: These results suggest that shift work may increase systolic blood pressure levels among Japanese men.     

Short sleep duration among workers--United States, 2010

Insufficient sleep can have serious and sometimes fatal consequences for fatigued workers and others around them. For example, an estimated 20% of vehicle crashes are linked to drowsy driving. The National Sleep Foundation recommends that healthy adults sleep 7-9 hours per day. To assess the prevalence of short sleep duration among workers, CDC analyzed data from the 2010 National Health Interview Survey (NHIS). The analysis compared sleep duration by age group, race/ethnicity, sex, marital status, education, and employment characteristics. Overall, 30.0% of civilian employed U.S. adults (approximately 40.6 million workers) reported an average sleep duration of ≤6 hours per day. The prevalence of short sleep duration (≤6 hours per day) varied by industry of employment (range: 24.1%-41.6%), with a significantly higher rate of short sleep duration among workers in manufacturing (34.1%) compared with all workers combined. Among all workers, those who usually worked the night shift had a much higher prevalence of short sleep duration (44.0%, representing approximately 2.2 million night shift workers) than those who worked the day shift (28.8%, representing approximately 28.3 million day shift workers). An especially high prevalence of short sleep duration was reported by night shift workers in the transportation and warehousing (69.7%) and health-care and social assistance (52.3%) industries. Targeted interventions, such as evidence-based shift system designs that improve sleep opportunities and evidence-based training programs on sleep and working hours tailored for managers and employees, should be implemented to protect the health and safety of workers, their coworkers, and the public.     

Melatonin, sleep, and shift work adaptation

BACKGROUND: Night work is associated with disrupted circadian rhythms, fatigue, accidents, and chronic disease. Melatonin secretion helps regulate sleep and circadian rhythms. OBJECTIVE: Melatonin, sleep disturbances, and symptoms (sleep, fatigue, mental) were compared among workers on permanent day, swing, and night shifts. METHODS: Urinary 6-hydroxymelatonin sulfate (6-OHMS) was measured in postwork and postsleep samples. Disrupted circadian melatonin production was evaluated using the sleep:work 6-OHMS ratio. Wrist actigraphy characterized light exposures and sleep characteristics. RESULTS: Night workers had altered melatonin, disrupted sleep, and elevated symptom prevalence. Subjects grouped by their sleep:work 6-OHMS ratio rather than shift had even greater symptom prevalence. Risks for two or more symptoms were 3.5 to 8 times greater among workers with sleep:work ratios < or =1 compared to those with ratios >1. CONCLUSIONS: This ratio may help identify workers at increased risk for accidents or injuries.     

Circadian excretory rhythms in night workers

Conroy, R. T. W. L., Elliott, A. L., and Mills, J. N. (1970).Brit. J. industr. Med.,27, 356-363. Circadian excretory rhythms in night workers. Urine samples have been collected from day and night shift workers in a light engineering factory over periods of 24 or 48 hours during which blood was also collected for determination of plasma 11-hydroxycorticosteroids (11-OHCS). Different subjects divided their 24-hour output into as few as 4 or as many as 14 portions. Where possible, the timing of the excretory rhythms was assessed objectively by fitting a sine curve. The potassium excretory rhythm was, in most subjects, well adapted to night work in that they excreted least during their hours of sleep; no relationship could be discerned between potassium excretory and plasma 11-OHCS rhythms. The sodium excretory rhythm was less regular than that of potassium in both night and day workers, and in night workers both sodium excretion and urine flow were often high during the hours of sleep, so that the subjects were sometimes awakened by the need to micturate. There was, however, sufficient association between the behaviour of sodium and potassium to suggest that their excretory rhythms have a common cause, and that this is not the secretion of 11-OHCS. Phosphate excretion fell sometimes on rising, even though plasma 11-OHCS concentration was not high, and sometimes after a high level of plasma 11-OHCS, at a time other than on rising. This suggests that these are two independent contributory causes of the usual morning fall in phosphate excretion.     

Duration of sleep depending on the type of shift work

Summary Time budget studies were performed in eight groups of shift workers. The 9,480 diary records of altogether 1,230 shift workers were analyzed and related to corresponding shift types. The shortest night sleep was found before the morning shift (mean 7.0 h). There were large differences in the duration of day sleep when classifying this sleep into specific types, as day sleep before 1st night shift (mean 2.1 h), between two night shifts (mean 6.1 h), or after last night shift (mean 4.2 h). Average sleep durations of five kinds of day sleep and 12 kinds of night sleep are presented together with 14 frequency distributions of durations of sleep.It is concluded that there should not be many night shifts in succession and that morning shifts should not begin too early to avoid an accumulation of sleep deficits.Dedicated to Dr. H. Loskant on the occasion of his 65th birthday     

Meals, snacks and food choices in Brazilian shift workers with high energy expenditure

Objective To describe the food intake of garbage collectors, who works in three shifts, in terms of meal and snack frequency, content, time distribution and the contribution of various popular foods to the total diet. Methods Sixty‐six Brazilian garbage collectors, who work in morning, afternoon, and night shift, participated in the present study. The quantitative methods used were a combination of one 24‐h recall and two 24‐h records during three nonconsecutive work days. The qualitative method used was the food‐based classification of eating episodes model modified in order to define meals or snacks in three categories of events: meals with three food groups of high nutrient density (three HND meals), meals with two food groups of high nutrient density (two HND meals) and snacks, composed of only one food category of high nutrient density. Results The total number of eating events per day was significantly higher for night shift workers. Over 24‐h, ‘two HND meals’ were the most common events and contributed the most energy, in all three shifts. Night shift workers ate more at dawn and less in the morning than other shifts. In all three shifts, meat was the most important food contributing to energy intake. Conclusion Different work schedules did not affect the relative frequency of meal types and snacks or their contribution to daily energy intake, but affected the daily distribution of eating events, with a redistribution of intake from day to night in night shift workers.     

倒班和睡眠时间对钢铁工人肝功能异常的影响

  目的  探讨倒班、平均睡眠时间及其联合作用对钢铁工人肝功能异常的影响,为保护钢铁工人肝脏提供理论依据。  方法  采用横断面研究,以某钢铁公司6 907名工人作为研究对象, 并收集信息。采用非条件Logistic回归分析模型和限制性立方样条函数进行分析。  结果  肝功能异常的检出率为18.0%,且男性高于女性(19.2% vs. 5.1%)。调整混杂因素后,倒班年限和肝功能异常之间存在非线性剂量反应关系。倒班和平均倒班频率＞7夜/月患肝功能异常的风险分别增加1.24倍(OR=1.24, 95% CI: 1.04~1.49)和1.29倍(OR=1.29, 95% CI: 1.07~1.56)。以倒班状态分层,在倒班工人中平均睡眠时间较短(≤5 h/d)和较长(＞7 h/d)患肝功能异常的风险分别增加1.19倍(OR=1.19, 95% CI: 1.01~1.43)和1.22倍(OR=1.22, 95% CI: 1.02~1.44)。且平均睡眠时间较长或较短均与倒班存在正向相乘的交互作用。根据平均睡眠时间分层后,平均睡眠时间＞5~7 h/d的各倒班指标与肝功能异常的联系无统计学意义。  结论  倒班工作和睡眠时间较长或较短联合作用会增加钢铁工人肝功能异常的风险,倒班工作对肝功能异常的独立作用也不容忽视。     

Age and adjustment to night work.

OBJECTIVE--The study was designed to examine the effects of age on sleep and the circadian rhythms during consecutive night shifts. METHODS--Two groups of letter sorters (19-29 (n = 7) and 53-59 (n = 7) years of age were studied in a sleep laboratory under closely controlled conditions. After two baseline days, circadian adjustment to three night shifts was monitored by continuous measurement of rectal temperature, salivary melatonin, and sleep-wakefulness during the night shifts. RESULTS--Age was significantly related to the adjustment to night work of rectal temperature minimum and of self rated sleepiness. Young subjects delayed their temperature phase and decreased sleepiness more than the older subjects. Age was also significantly related to an increase of alertness and to the feeling of being refreshed after the day sleep. Although there were basic differences in sleep duration and structure between the age groups, the latter did not change across the night shifts. CONCLUSION--Aging decreases the ability to recover after several, but not after the first night shift.     

Shift and Day Work: A Comparison of Sickness Absence, Lateness, and other Absence Behaviour at an Oil Refinery from 1962 to 1965

Despite the increasing use of continuous process shift work in modern industry, few studies on the medical aspects of shift work can be found in recent literature of occupational health. Physiologists have shown that the ability of the body to adjust its circadian rhythms to alteration in hours of work or sleep can take up to a month. The usual type of shift work in industry involves weekly changes of hours, and thus on theoretical grounds at least this may not be the most suitable frequency for shift changes.

Sickness absence of male refinery workers has been studied over a four-year period. The figures show that continuous three-cycle shift workers have consistently and significantly lower rates of sickness than day workers in similar occupations. The annual inception rate (spells) standardized for age was 108% for shift workers and 182% for day workers, and the average annual duration per man was 11 days for shift workers and 18 days for day workers, although the average length of spell was slightly longer among shift workers. As far as is known, such a difference has not been described before in detail.

Age-related lateness and absenteeism have been measured and show similar wide differences between the two groups.

Although both types of worker are largely self-selected, the difference is not due to medical selection or to an excess of any one type of disease in day workers. Over three-quarters of 150 shift workers interviewed stated that they preferred shift work hours and that sleeping difficulties were not common.

It is suggested that the main reasons for the difference between shift and day workers' sickness absence lie in the degree of personal involvement in the work and in the social structure of the working group.

     

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.     

Shiftwork and mortality from ischaemic heart disease.

OBJECTIVES: To investigate the relation between shift work and death from ischaemic heart disease (IHD). METHODS: A nested case-control approach was used. The cohort comprised male manual workers who joined an industrial company aged 50 years or under between 1 January 1950 and 31 December 1992 and worked there for at least one month. Cases were 467 cohort members who died during the same period aged 75 years or under, with ischaemic heart disease (IHD) (international classification of diseases (ICD) 410-414) coded from the death certificate. For each case a control worker was chosen, who joined the company at the same age and in the same period but who survived the case. Work status (shift work or day work) was assigned to cases for their entire employment and to controls for that part of their employment which preceded the matching case's death. The main source of information was historical personnel records containing pay codes which differed for day work and shift work. Information on weight, height, blood pressure, and smoking from a pre-employment medical was available. RESULTS: Two thirds of subjects had been employed for at least one month as shift workers and there was evidence that they had slightly better health at recruitment than day workers. The odds ratio for shift workers during the period starting 10 years after shift work began, and after adjustment for height, body mass index, blood pressure, smoking, duration of employment, and job status (skilled or unskilled) was 0.90 (90% confidence interval (90% CI): 0.68-1.21). There was no relation between risk of IHD death, and duration of shift work, but there was evidence of a reduced risk when actively employed as a shift worker, together with an increased risk in the first five years after leaving shift work to do day work. CONCLUSIONS: Shift work did not increase the risk of death from ischaemic heart disease in this study. Those workers with poorer cardiovascular health may be under represented in groups with longer shift work experience because of health related selection out of shift work.     

Randomized placebo-controlled field study of the effects of bright light and melatonin in adaptation to night work

OBJECTIVES: This study evaluated the effects of bright light and melatonin on adaptation to night work on an oil rig in the North Sea. METHODS: Seventeen persons working a schedule of 2 weeks on a 12-hour shift, with the first week on night shift and the second week on day shift (ie, the swing shift schedule) participated. In a randomized controlled crossover design, the shift workers received a placebo, melatonin (3 mg, 1 hour before bedtime), or bright light (30-minute exposure, individually scheduled) during the first 4 days on the night shift and during the first 4 days on the day shift. Subjective and objective measures of sleepiness (Karolinska Sleepiness Scale and a simple serial reaction-time test) and sleep (diary and actigraphy) were recorded. RESULTS: Subjective measures indicated that melatonin modestly reduced sleepiness at work during the day shift and increased sleep by 15-20 minutes per day. Bright light gave values in between those of melatonin and the placebo, but with few significant results. According to the objective measures, bright light improved sleep to a minor degree during the night shift. Hardly any side-effects were reported. CONCLUSIONS: Melatonin and bright light modestly improved sleep and sleepiness in this field study. In well-controlled simulated nightwork studies, both melatonin and bright light are more effective in alleviating sleepiness and sleep problems. The less effect in this field study may be due to competing or conflicting factors present in real life or to an inoptimal timing and duration of the treatments.     

Effects of diurnal and seasonal sleep deficiency on work effort and fatigue of shift workers

Summary This study was designed to assess and compare the quantity and quality of sleep of morning, afternoon, and night shift workers during the winter and summer seasons, and to evaluate the effects of sleep deficiency on the work effort and fatigue of the workers. The subjects studied consisted of a sample of 150 textile workers, working on a monthly rotating 3-shift system: morning shift (06.00–11.00 and 14.00–17.00) afternoon shift (11.00–14.00 and 17.00–22.00), and night shift (22.00–06.00). Information concerning quantity and quality of sleep were registered daily over a week for every subject. The Ratings of Perceived Effort scale and the Feeling and Symptoms of Fatigue scale were used to collect information about feeling of effort and fatigue of the subjects. The results showed that the duration of sleep length is longest in the afternoon and shortest in the night shift both during summer and winter. The amount of sleep is shorter during summer during all three shifts. The workers spent more effort and felt more fatigued during summer than winter. The shift workers, particularly of the tropical region, like Bangladesh, seem to be worst affected in terms of quantity and quality of sleep, health and well-being due to extremely high temperature (30–45° Celsius) during summer than winter (5–25° Celsius). The workers think that the problems of shift work could be minimized by improving the quality of working and living conditions, reducing cycle of rotation, shortening working day and closing night shift during peak summer.     

Dietary Carbohydrate and Nocturnal Sleep Duration in Relation to Children’s BMI: Findings from the IDEFICS Study in Eight European Countries

Previous research has found an association between being overweight and short sleep duration. We hypothesized that this association could be modified by a high carbohydrate (HC) diet and that the timing and type (starch or sugar) of intake may be an important factor in this context. Participants in the prospective, eight-country European study IDEFICS were recruited from September 2007 to June 2008, when they were aged two to nine years. Data on lifestyle, dietary intake and anthropometry were collected on two occasions. This study included 5944 children at baseline and 4301 at two-year follow-up. For each meal occasion (morning, midday, and evening), starch in grams and sugar in grams were divided by total energy intake (EI), and quartiles calculated. HC-starch and HC-sugar intake categories were defined as the highest quartile for each meal occasion. In a mutually adjusted linear regression model, short sleep duration as well as HC-starch in the morning were positively associated with body mass index (BMI) z-scores at baseline. HC-starch at midday was positively associated with body mass index (BMI) z-scores in children with short sleep duration, and negatively associated with BMI z-scores in those with normal sleep. After adjustment for baseline BMI z-scores, associations between total HC from starch or sugar and high BMI z-scores at two-year follow-up did not persist. Our observations offer a perspective on optimal timing for macronutrient consumption, which is known to be influenced by circadian rhythms. Reduced carbohydrate intake, especially during morning and midday meals, and following nocturnal sleep duration recommendations are two modifiable factors that may protect children from being overweight in the future.     

Sleep and wakefulness in a group of shift workers

Tune, G. S. (1969).Brit. J. industr. Med.,26, 54-58. Sleep and wakefulness in a group of shift workers. Fifty-two shift workers recorded their hours of sleep and wakefulness for a period of 10 weeks. Compared with matched non-shift-working control subjects it was found that they took a higher average duration of sleep per 24 hours and more and longer naps outside the major sleep period. A comparison of the on and off duty records from the shift workers showed that a sleep debt was incurred during the former which was largely paid off by taking long naps in the latter. It is suggested that the longer sleep taken by shift workers may be necessary in order to pay off specific kinds of sleep debt.     

邢台市男性煤炭工人睡眠与肾功能异常的关系

  目的  探讨邢台市男性煤炭工人睡眠与肾功能异常之间的关系,为男性煤炭工人的肾脏疾病防治提供理论依据。  方法  采用现况研究,收集河北省邢台市2家煤炭公司的3 774名井下男性煤炭工人的问卷和血生化指标等信息。采用多因素Logistic回归分析模型分析倒班、睡眠时长和失眠或睡眠评分与肾功能异常的关系。  结果  男性工人的肾功能异常检出率为5.3%,倒班、睡眠时长≤5 h、失眠的工人占比分别为63.2%、4.0%及10.0%。调整年龄、睡眠时长、倒班状态、失眠等因素后,多因素Logistic回归分析模型分析结果显示,现在倒班(OR=1.557, 95% CI: 1.078~2.250, P=0.018)、睡眠时长≤5 h(OR=1.886, 95% CI: 1.005~3.540, P=0.048)、有睡眠问题组(OR=1.810, 95% CI: 1.286~2.546, P=0.001)与肾功能异常的联系减弱,失眠与肾功能异常联系无统计学意义(P=0.279)。根据倒班状态进行分层分析,调整相关混杂因素后发现,现在倒班的煤炭工人肾功能异常患病风险随睡眠评分等级的增加而增加(P_趋势=0.001)。  结论  每天睡眠时长≤5 h、现在倒班与男性煤炭工人肾功能异常独立相关,且睡眠问题越严重,肾功能异常的患病风险越高。     

Circadian rhythms in plasma concentration of 11-hydroxycorticosteroids in men working on night shift and in permanent night workers

Conroy, R. T. W. L., Elliott, Ann L., and Mills, J. N. (1970).Brit. J. industr. Med.,27, 170-174. Circadian rhythms in plasma concentration of 11-hydroxycorticosteroids in men working on night shift and in permanent night workers. Blood samples have been collected for estimation of plasma 11-hydroxycorticosteroids from three groups of workers - day and night shift workers in a light engineering factory, and night workers in a newspaper printing works. Up to five samples were collected over 24 hr, or two samples per 24 hr were collected for three days. In conformity with the observations of others, day workers showed maximal concentrations in the morning around the time when they started work. In the newspaper workers maximal concentrations were found when they awoke around 14·00 hr. Night shift workers in the engineering works showed a greater variety of pattern, some showing the pattern usual in a day worker, some showing a maximum concentration about midnight and a minimum around 06·00 hr and a large proportion showing no clear circadian rhythm.

In the newspaper workers the rhythm was thus well adapted to their pattern of nocturnal work, whereas relatively few of the night shift workers in the engineering works showed such adaptation. It appears that the adrenal cortical rhythm can be adapted to night work in a community in which this is universal, accepted and lifelong, but that such adjustment is unusual in men on night shift work for limited periods, and whose associates are mainly following a usual nycthemeral existence.

     

Tolerance to shift work—how does it relate to sleep and wakefulness?

Objectives There is limited knowledge as to why some individuals tolerate shift work and others do not. As a consequence of their intolerance, many individuals develop dissatisfaction with their shift schedule. To evaluate if dissatisfaction with ones shift system was related to alterations of the daily pattern of sleep and sleepiness, we followed two groups of shift workers that were either highly satisfied or dissatisfied with their shift schedule, during an entire shift cycle.Methods Thirty-six male and 20 female shift workers were selected according to their satisfaction with their shift schedule. The shift cycle included seven work periods (triads of shifts; night shift—afternoon shift—morning shift), with only 8–9 hours off (quick returns) between shifts, but followed by a day off.Results Sleep length was reduced after night shifts (4.8 h) and afternoon shifts (5.4 h). Sleepiness was increased during all shifts, particularly night shifts. Sleepiness did not accumulate across the shift cycle even though sleepiness was slightly increased directly after the last triad of shifts. There were few significant gender differences. Dissatisfied shift workers reached much higher levels of sleepiness and reported less sufficient sleep, but not objectively poorer or shorter sleep. Amongst dissatisfied workers, this resulted in an increase of sleepiness problems across shifts within the triad of shifts. Dissatisfied workers also had more performance lapses at the end of the night shift.Conclusions Satisfaction with the shift schedule seems to reflect how well the shift workers were coping with the schedule. It is suggested that the increase of sleep/wake problems within the work period for the dissatisfied shift workers is related to increased sensitivity to curtailed and displaced sleep.     

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.