Shiftwork tolerance and circadian rhythms in oral temperature and heart rate

Abstract

The study aimed at establishing differences in the circadian rhythm parameters of oral temperature and heart rate between three groups of workers matched by age: tolerant shiftworkers with good sleep quality and few psychosomatic and digestive complaints, intolerant shiftworkers with poor sleep quality and more psychosomatic and digestive complaints, and workers who had never worked in shifts. The study was performed at an oil refinery recreation centre where the subjects were isolated for three days. During that period they lived under constant conditions, i.e. their activities, timing and content of meals, ambient temperature and light were controlled. Hourly measurements of oral temperature and heart rate were performed over a 24-h period. The parameters of the physiological rhythms were estimated by means of the COSINA method. Generally, the differences between the groups were low and not statistically significant. The authors could find no difference in the amplitude and phase position between the tolerant shiftworkers unlike other authors. The difference between these results and those of others is likely to be due to the fact that earlier studies were performed in field conditions where many factors that could have masked the results were not controlled for.     

Relationships among shiftworker eating habits,eating satisfaction,and self-reported health in a population of US miners

Abstract

As part of a larger study on the health and safety of shiftworkers in the mining population by the US Bureau of Mines, the association between meal frequency, meal regularity, eating satisfaction and a self-reported health index was examined. Although the link between shiftwork and some health complaints, such as gastrointestinal disorders, has been established, the research needed to understand why this occurs has not been fully undertaken. Specifically, academic nutritional research has substantially ignored the question of how working irregular hours affects the eating behavior of industrial workers such as miners. In this study the eating habits of 101 surface mine workers were studied. It was found that working the day, afternoon/evening, and night-shifts was related to the number of meals eaten on those shifts and to the consistency of timing of those meals. The lowest eating satisfaction levels were reported by those who ate at different times on all shifts and who changed the number of meals eaten per day on each shift. Lowest self-reported health ratings were reported by those who changed the number of meals taken on each shift, rather than by those who ate one, two or three meals per day. These results are discussed in relation to the possible mechanisms contributing to gastrointestinal disorders and to coping mechanisms that could be adopted by shiftworkers.     

Nutrient intake in day workers and shift workers

Abstract

The 24-h dietary intake, nutritional status parameters and psychosomatic factors of two-shift, three-shift and day workers were compared. Estimations of the dietary intake (across a work cycle) were made by use of a nutrient database. No significant differences were found between the groups for a large number of nutritional variables: intake of energy; intake and percentage of energy from protein, fat, total carbohydrates and sucrose; intake of coffee; and intake and density of vitamins and minerals. Only minor differences were found between the groups with regard to the quantitative intake of alcohol and calcium, and with regard to the quality of the diet (percentage of energy from alcohol, density of calcium). The groups differed significantly with respect to attitude towards work hours (three-shift workers being most negative in their attitude) and sleep disturbances (shift workers being most negative). The three-shift workers were more evening-oriented and they had higher concentrations of glucose in their blood. It was concluded that work hours not related to nutritional intake—at least not when total amounts across time are considered. It was also concluded that work hours were not related to Body Mass Index or blood lipids: triglycerides, total cholesterol, LDL (low-density lipoprotein) cholesterol and HDL (high-density lipoprotein) cholesterol.     

Is tolerance to shiftwork predictable from individual difference measures?

Abstract

This study was aimed at evaluating the most important relations between individual characteristics of shiftworkers and their subjective health complaints, obtained by cross-sectional and longitudinal procedures. A total of 604 shiftworkers and 185 young subjects who were going to enter shiftwork were examined by means of individual difference and subjective health questionnaires. The questionnaires were administered concurrently to the group of workers already involved in shiftwork. In the other group studied, the questionnaires were administered before they entered shiftwork, and subjective health was re-examined after the first and third year of work on shifts. More health complaints were reported by the group of older workers and those with longer shiftwork experience, with higher scores of neuroticism, hard-driving and competitiveness, speed and impatience, and rigidity of sleeping habits, and lower scores on relaxedness, efficiency and vigorousness. However, the correlations between these dimensions, when taken before entering shiftwork, and subjective health complaints obtained after a few years working on shifts were small or absent, indicating low validity of the individual difference measures for predicting subsequent health problems in shiftworkers.     

Sleep and napping in young shiftworkers: A 5-year follow-up

Abstract

The present study examined sleep characteristics in young workers who entered rapidly rotating shiftwork for the first time and stayed on shifts for 5 years. Data were collected when the subjects had shiftwork experience of approximately 1.5, 3.5 and 5.5 years and a mean age of 22, 24 and 26 years. Data are presented showing significant differences in the main sleep durations between situations within the shift cycle and a small reduction in overall sleep over the observed period, primarily due to a sleep reduction on afternoon shift days. Data on sleep quality did not show any change over this early period of shiftwork exposure. In addition, napping strategies did not change, with the exception of a small increase in those taking naps on night-shift days between 1.5 years and 3.5 years of shiftwork exposure. At all the observed phases there were more young shiftworkers taking a nap on the morning shift days than on the night-shift days. The data suggested that reduced sleeps on morning and night-shift days were not compensated by taking a nap, but rather with an increase in main sleep duration on afternoon shift days and days off. A weak tendency for individuals to be relatively long or short sleepers irrespective of sleep conditions could be seen.     

Nutrient intake in day workers and shift workers

The 24-h dietary intake, nutritional status parameters and psychosomatic factors of two-shift, three-shift and day workers were compared. Estimations of the dietary intake (across a work cycle) were made by use of a nutrient database. No significant differences were found between the groups for a large number of nutritional variables: intake of energy; intake and percentage of energy from protein, fat, total carbohydrates and sucrose; intake of coffee; and intake and density of vitamins and minerals. Only minor differences were found between the groups with regard to the quantitative intake of alcohol and calcium, and with regard to the quality of the diet (percentage of energy from alcohol, density of calcium). The groups differed significantly with respect to attitude towards work hours (three-shift workers being most negative in their attitude) and sleep disturbances (shift workers being most negative). The three-shift workers were more evening-oriented and they had higher concentrations of glucose in their blood. It was concluded that work hours not related to nutritional intake—at least not when total amounts across time are considered. It was also concluded that work hours were not related to Body Mass Index or blood lipids: triglycerides, total cholesterol, LDL (low-density lipoprotein) cholesterol and HDL (high-density lipoprotein) cholesterol.     

Relationships among shiftworker eating habits, eating satisfaction, and self-reported health in a population of US miners

As part of a larger study on the health and safety of shiftworkers in the mining population by the US Bureau of Mines, the association between meal frequency, meal regularity, eating satisfaction and a self-reported health index was examined. Although the link between shiftwork and some health complaints, such as gastrointestinal disorders, has been established, the research needed to understand why this occurs has not been fully undertaken. Specifically, academic nutritional research has substantially ignored the question of how working irregular hours affects the eating behavior of industrial workers such as miners. In this study the eating habits of 101 surface mine workers were studied. It was found that working the day, afternoon/evening, and night-shifts was related to the number of meals eaten on those shifts and to the consistency of timing of those meals. The lowest eating satisfaction levels were reported by those who ate at different times on all shifts and who changed the number of meals eaten per day on each shift. Lowest self-reported health ratings were reported by those who changed the number of meals taken on each shift, rather than by those who ate one, two or three meals per day. These results are discussed in relation to the possible mechanisms contributing to gastrointestinal disorders and to coping mechanisms that could be adopted by shiftworkers.     

Perceived exertion under conditions of sustained work and sleep loss

Abstract

The rated perceived exertion (RPE) for treadmill walking carrying a 22 kg pack was measured in two studies with heart rate, workload and psychological measures. Study 1 used an initial treadmill speed and grade producing 40% of maximal oxygen consumption. Exercise subjects walked 1/2-h, then did other tasks for 20-h for 16 sessions on two 20 h long days. Group I had a 4 h nap, while Group 2 had 4 h of rest between workdays. Subjects maintained the 40% workload throughout the two days with a 3 h nap between days, one group starting exercise at midnight and one at noon.

A steady increase in RPE over the sessions each day was found in each study. There were no differences in RPE between the Nap and Rest groups in Study 1 or between the midnight and noon groups in Study 2. RPE was higher on Day 2 in each study. RPE correlated significantly with heart rate, distance walked or elevation at most time periods on the first workday in Study 1, but not Study 2. RPE was positively correlated with fatigue, symptoms, sleepiness and negative mood, and negatively correlated with vigor at most of the time periods day 1 in Study 2; with similar significant correlations at only one time period on day 1, Study 1. RPE was lower the first session Day 2 as compared to the last session Day 1 in both studies. This pre-post break recovery did not differ between groups in either study.     

Is tolerance to shiftwork predictable from individual difference measures?

This study was aimed at evaluating the most important relations between individual characteristics of shiftworkers and their subjective health complaints, obtained by cross-sectional and longitudinal procedures. A total of 604 shiftworkers and 185 young subjects who were going to enter shiftwork were examined by means of individual difference and subjective health questionnaires. The questionnaires were administered concurrently to the group of workers already involved in shiftwork. In the other group studied, the questionnaires were administered before they entered shiftwork, and subjective health was re-examined after the first and third year of work on shifts. More health complaints were reported by the group of older workers and those with longer shiftwork experience, with higher scores of neuroticism, hard-driving and competitiveness, speed and impatience, and rigidity of sleeping habits, and lower scores on relaxedness, efficiency and vigorousness. However, the correlations between these dimensions, when taken before entering shiftwork, and subjective health complaints obtained after a few years working on shifts were small or absent, indicating low validity of the individual difference measures for predicting subsequent health problems in shiftworkers.     

Editorial: Women and work

Abstract

When compared to day workers, night-shift workers report that they eat fewer meals, have poorer appetites, are less satisfied with their eating habits, and eat at different times of the day. When demographic variables are held constant, there do not appear to be any significant differences between experienced day and night-shift workers in caffeine or alcohol consumption. Exceptions to and variations in these findings are probably due to the background influences of social and cultural variables. Eating and drinking behaviours do effect human performance and mood, but little relevant data have been gathered from experienced night-shift workers. There are no shiftworker data evaluating the effectiveness of the special diets or dietary recommendations that have been proposed for use by night-shift workers. Thus, attempts to manipulate night-shift worker eating and drinking habits require experimental test.     

Shiftwork effects in nuclear power workers: A field study using portable computers

Abstract

This field study of nuclear power shiftworkers reports the use of hand-held computers to record alertness levels, cognitive task performance and workload ratings. Subjective ratings and performance tasks (Search and Memory-5 (SAM-5); Choice Reaction Time (CRT) were completed on the computers at 2-h intervals during selected shifts in the work schedule by maintenance crews and reactor operators. Sleep duration and quality data were also obtained during the 35-day shift cycle. Workload remained relatively stable across shifts. The night-shift was associated with shorter sleep durations and poorer sleep quality. Significantly lower levels of alertness and poorer perforniance for components of the performance tasks were also observed on the night-shift. Tinic-on-shift effects on alertness were evident, where by for the night-shift, especially, alertness dropped dramatically during the early hours. Components of SAM-5 performance showed differential time-on-shift patterning relative to each shift whereas CRT was unresponsive to time-on-shift effects. Significant variations were observed in alertness and performance components during the 12-h night-shift. Perhaps paradoxically, performance on the 12-h night-shift appeared to improve rather than deteriorate during the early-hour period that was associated with the greatest drop in alertness. This was suggestive of extra effort expenditure during this critical period.     

Perceived exertion under conditions of sustained work and sleep loss

The rated perceived exertion (RPE) for treadmill walking carrying a 22 kg pack was measured in two studies with heart rate, workload and psychological measures. Study 1 used an initial treadmill speed and grade producing 40% of maximal oxygen consumption. Exercise subjects walked 1/2-h, then did other tasks for 20-h for 16 sessions on two 20 h long days. Group I had a 4 h nap, while Group 2 had 4 h of rest between workdays. Subjects maintained the 40% workload throughout the two days with a 3 h nap between days, one group starting exercise at midnight and one at noon.

A steady increase in RPE over the sessions each day was found in each study. There were no differences in RPE between the Nap and Rest groups in Study 1 or between the midnight and noon groups in Study 2. RPE was higher on Day 2 in each study. RPE correlated significantly with heart rate, distance walked or elevation at most time periods on the first workday in Study 1, but not Study 2. RPE was positively correlated with fatigue, symptoms, sleepiness and negative mood, and negatively correlated with vigor at most of the time periods day 1 in Study 2; with similar significant correlations at only one time period on day 1, Study 1. RPE was lower the first session Day 2 as compared to the last session Day 1 in both studies. This pre-post break recovery did not differ between groups in either study.     

Editorial statement: Stress and work compensation

Shift work has been reported to predict health problems, and a possible explanation is that shift work may lead to poorer health habits, thereby increasing a person's vulnerability to illness. This study examined the association between shift work and health habits, as indicated by smoking, alcohol intake, physical activity and by being overweight. A questionnaire was sent to all 2795 female nurses working in the 10 hospitals of two Finnish health care districts. From the 2299 respondents, we selected those 506 shift workers who reported having always done shift work and those 183 day workers who had never done shift work. Shift workers were found to smoke more and to be overweight more often than day workers. These differences gradually increased in each successive age group, being 1.94 pack-years in smoking and 0.9 kg m^-2 in body mass index among nurses over 45 years of age. Shift work was not associated with alcohol intake or sedentary lifestyle. This evidence is compatible with the possibility that shift work in nurses increases smoking and being overweight to a degree that contributes to health problems, including coronary heart disease.     

Modification of shiftwork effects by chemical workplace exposure

Abstract

Possible chronotoxic effects were the reason to study chemical workplace exposure under the special condition of shiftwork. Eight shiftworkers occupationally exposed to acetone vapours and eight controls were investigated during fast-rotated shiftwork. The mean concentration of acetone during the shifts was close to 1000 ppm (2400 mg/m³). Data on well-being and acute symptoms, but not on performance, indicate that the exposure contributed mainly in an additive way to the negative effects of shiftwork. As a consequence, the exposed shiftworkers revealed enhanced impairments during the night-shift.     

Appropriate use of bright light promotes a durable adaptation to night-shifts and accelerates readjustment during recovery after a period of night-shifts

Abstract

The present study examines the stability of bright light circadian readjustment during two consecutive dim light night-work periods and circadian synchronization during the recovery after a night-shift period. A sample of 10 subjects was divided into 2 groups (control group: 6 subjects; experimental group: 4 subjects). All subjects worked during 5 days, between 23:00 and 07:00 h and then went to sleep. Subjects received 2500-3000 lux between 02:00 and 05:00 h during 5 days for the control group and 3 days for the experimental group. During recovery after the night-shift periods, three cycles of bright light were administered at two different times: 12:00-15:00 h for two of six subjects from the control group and 10:00-13:00 h for all subjects (4) of the experimental group. By the fifth cycle of night-work the maximum of urinary aMT6s excretion that occurs at 05:00 h in the baseline condition was shifted to 12:00 h for the control and experimental groups (delay in hours: 7±1.6 (control); 7±1 (experimental)). This result suggests that three cycles of bright light are sufficient to induce a significant phase delay and that this delay remained stable when night-work proceeded under dim light. The phase delay of the circadian aMT6s excretion by exposure to bright light was accompanied by an improvement of the quality of day sleep and level of cognitive and psychomotor performances for control and experimental groups. No significant difference was observed in the two groups for daytime sleep and nocturnal performance. The two bright light periods used during the three days of recovery induced a complete synchronization in five of six subjects. One subject showed a partial synchronization probably because he remained at the laboratory under dim light during the day and had few family and social contacts.     

Effects of age and domestic commitment on the sleep and alertness of female shiftworkers

Abstract

In this study, the combined effects of age and domestic commitment on sleep duration, sleep difficulties and alertness in a sample of female shiftworkers were studied. A total of 572 nurses working in general hospitals in England completed a questionnaire. Two main shift systems were worked by the nurses: permanent nights or rotating shifts. Initial analysis revealed significant differences between these two groups of nurses, resulting in separate analysis of each group. Regression analysis showed that although older nurses had shorter sleep duration they did not report more sleep difficulties, in addition, their overall on-shift alertness was higher compared to younger nurses. Domestic commitment, defined as the number of dependants in the household and the level of perceived work-home conflict, not only reduced sleep duration, but also resulted in more sleep difficulties and lower on-shift alertness for most of the shifts. Two implications with regards to the relationship between age and sleep are discussed. First, the study points to the relevance of considering both biological and social factors when looking at age and sleep. Secondly, the study shows that the effects of age on sleep duration and sleep difficulties are not similar. This finding requires further research, especially in the light of the higher levels of alertness reported by older nurses.     

Effects of sleep inertia on cognitive performance following a 1-hour nap

Abstract

This study investigated the effects of a 1-h nap on subsequent performance in spatial memory (SM) and logical reasoning (LR) tasks. The objective was to evaluate the duration of the effects of sleep inertia (SI). The performance was measured in two independent groups of subjects. The 1-h nap took place at 00:00 h in group 1 and at 03:00 h in group 2. In each task, the experimental design comprised one no-nap condition in which subjects had no sleep before the night tests, and a nap condition that comprised the 1-h nap followed by the test sessions. To measure the duration of SI effects, the subjects were tested in two 30-min sessions and the data in each session were analysed in sub-units of time of 3 min each. In each task the results showed no effects on accuracy, and no circadian effects of napping were found. In each task, analyses of pooled data of the two groups showed that the performance in the 1-h nap condition exhibited significant reductions of speed immediately following awakening, when compared with no-nap, reflecting SI effects. In SM, the slowing lasted 24 min, and 27 min in LR. Practical implications of the results are discussed.     

Men and women who like continuous shiftwork are more ‘hardy’: But what does it mean?

Abstract

Continuous shiftworkers of both genders who like shiftwork and report fewer digestive problems have higher scores on hardiness than those who dislike shiftwork. Whether this is a causal, consequential or accidental relationship requires a longitudinal investigation. It is also not clear how far ‘hardiness’ is a personality measure, a behavioural style, a coping strategy, or a consequence of the stress of shiftwork.     

Do eating and drinking habits interact with work schedule variables?

When compared to day workers, night-shift workers report that they eat fewer meals, have poorer appetites, are less satisfied with their eating habits, and eat at different times of the day. When demographic variables are held constant, there do not appear to be any significant differences between experienced day and night-shift workers in caffeine or alcohol consumption. Exceptions to and variations in these findings are probably due to the background influences of social and cultural variables. Eating and drinking behaviours do effect human performance and mood, but little relevant data have been gathered from experienced night-shift workers. There are no shiftworker data evaluating the effectiveness of the special diets or dietary recommendations that have been proposed for use by night-shift workers. Thus, attempts to manipulate night-shift worker eating and drinking habits require experimental test.     

Exploring turnover intentions among three professional groups of employees

Abstract

Although considerable research effort has been devoted to understanding work attitudes, behaviours and outcomes regarding turnover intentions, little has been done to explore it across different professions. This study takes a step in this direction and examines the effect of affective commitment, job satisfaction and job performance on turnover intentions across three professions. To this end, we surveyed three professional groups of employees and managers: financial officers and social workers employed in the public sector and lawyers employed in the private sector. The results of these three studies show that turnover intentions vary across these professions. Social workers exhibit lower turnover intentions than financial officers and lawyers, who tend to exhibit high turnover intentions. In addition, we found that job satisfaction and affective commitment are negatively associated with turnover intentions, while no significant relationship was found to exist between job performance and turnover intentions. The implications of this study suggest that both researchers and practitioners should take into consideration not only the organizational context, but also the occupational context while exploring the process of voluntary turnover.