Effect of stress on the cardiovascular system activity in operators of predominantly mental work at different times of the day and the working week

The heart rate and systolic and diastolic blood pressures (HR, BP_s, and BP_d, respectively) were measured in controllers of electricity distribution at the beginning and end of 12-h shifts. Hemodynamic parameters were calculated. The stress was assessed with a five-point scale. It was found that the stress of mental work of the operator type activated the functioning of the cardiovascular system (CVS). The CVS reaction was more pronounced and interactive during the first shifts in each block than during the second shifts. The CVS reaction was more pronounced and interactive during day shifts than during night shifts. An increase in stress during the first day shifts was accompanied by a decrease in HR and an increase in minimum BP_d during the shift, in the absence of a BP_s reaction. The minimum levels of all three parameters (HR, BP_s, and BP_d) were increased during the first night shifts, which indicates that the effectiveness of CVS activation in the nighttime was decreased as compared to the daytime. The BP_d is specifically sensitive to the work stress of controllers: its reaction to an increase in stress is classic during the first shifts and inverted during the second night shifts. This reflects exhaustion of adaptation reserves. The HR showed attenuated reactivity during the daytime, but not during the nighttime, when it reacted in the classic way.     

Acute sleep deprivation and circadian misalignment associated with transition onto the first night of work impairs visual selective attention

Background

Overnight operations pose a challenge because our circadian biology promotes sleepiness and dissipates wakefulness at night. Since the circadian effect on cognitive functions magnifies with increasing sleep pressure, cognitive deficits associated with night work are likely to be most acute with extended wakefulness, such as during the transition from a day shift to night shift.

Methodology/Principal Findings

To test this hypothesis we measured selective attention (with visual search), vigilance (with Psychomotor Vigilance Task [PVT]) and alertness (with a visual analog scale) in a shift work simulation protocol, which included four day shifts followed by three night shifts. There was a nocturnal decline in cognitive processes, some of which were most pronounced on the first night shift. The nighttime decrease in visual search sensitivity was most pronounced on the first night compared with subsequent nights (p = .04), and this was accompanied by a trend towards selective attention becoming ‘fast and sloppy’. The nighttime increase in attentional lapses on the PVT was significantly greater on the first night compared to subsequent nights (p<.05) indicating an impaired ability to sustain focus. The nighttime decrease in subjective alertness was also greatest on the first night compared with subsequent nights (p<.05).

Conclusions/Significance

These nocturnal deficits in attention and alertness offer some insight into why occupational errors, accidents, and injuries are pronounced during night work compared to day work. Examination of the nighttime vulnerabilities underlying the deployment of attention can be informative for the design of optimal work schedules and the implementation of effective countermeasures for performance deficits during night work.     

Effects of chronic psychosocial stress on cardiac autonomic responsiveness and myocardial structure in mice

Repeated single exposures to social stressors induce robust shifts of cardiac sympathovagal balance toward sympathetic dominance both during and after each agonistic interaction. However, little evidence is available regarding possible persistent pathophysiological changes due to chronic social challenge. In this study, male CD-1 mice (n = 14) were implanted with a radiotelemetry system for electrocardiographic recordings. We assessed the effects of chronic psychosocial stress (15-day sensory contact with a dominant animal and daily 5-min defeat episodes) on 1) sympathovagal responsiveness to each defeat episode, as measured via time-domain indexes of heart rate variability (R-R interval, standard deviation of R-R interval, and root mean square of successive R-R interval differences), 2) circadian rhythmicity of heart rate across the chronic challenge (night phase, day phase, and rhythm amplitude values), and 3) amount of myocardial structural damage (volume fraction, density, and extension of fibrosis). This study indicated that there was habituation of acute cardiac autonomic responsiveness, i.e., the shift of sympathovagal balance toward sympathetic dominance was significantly reduced across repeated defeat episodes. Moreover, animals exhibited significant changes in heart rate rhythmicity, i.e., increments in day and night values and reductions in the rhythm amplitude, but these were limited to the first 5 days of chronic psychosocial stress. The volume fraction of fibrosis was sixfold larger than in control animals, because of the appearance of many microscopic scarrings. In summary, although mice appeared to adapt to chronic psychosocial stress in terms of acute cardiovascular responsiveness and heart rate rhythmicity, structural alterations occurred at the myocardial level.     

Adaptive potential of operators with various dynamics of fitness for work during a transition from day to night shift]

While transferring from day to night shifts 3 categories of changes in the working ability are revealed among the operators. It is stated that the working ability in 19% of operators decreases, in 62%--remains practically unchanged, in 19%--improves. The higher levels of arterial pressure, vascular peripheral resistance (in both shifts), the heart systole rate (day shift) are found in the first group of operators. The structure of correlations between the physiological functions is characterized by harder intrasystemic relations in the day shift as against that of other operators and by the increasing effects of the intersystemic interactions while decreasing intrasystemic relations in the night shift. The adaptive potentialities were higher in the second group and particularly in the third group of operators.     

Implementation of 12-hour shifts in a Brazilian petrochemical plant: impact on sleep and alertness

A recent worldwide trend in chemical and petrochemical industries is to extend the duration of shifts. Optimization of the labor force to reduce costs is one reason to increase the length of working time in a shift. Implementation of 12h shifts is a controversial decision for managers and scientists. Literature reviews show alertness is lower during the nighttime hours, and sleep duration is reduced and worse during the daytime. The main objective of this study was to evaluate the impacts of 12h shifts on alertness and sleep. To evaluate the duration and quality of sleep and alertness during work, 22 male shift workers on a continuous rotating schedule at a petrochemical plant completed activity logs and estimated alertness using analog 10-cm scales for 30 consecutive days, three times (at 2h, 6h, and 10h of the shift) every work shift. Statistical tests (analysis of variance [ANOVA] and Tukey) were performed to detect differences between workdays and off days. The shift schedule was 2 days/3 nights/4 off days, followed by 3 days/2 nights/5 off days, followed by 2 days/2 nights/5 off days. Sleep duration varied significantly (p < .001) among the work shifts and off days. Comparing work nights, the shortest mean sleep occurred after the second night (mean = 311.4 minutes, SD = 101.7 minutes), followed by the third night (mean = 335.3 minutes, SD = 151.2 minutes). All but one shift (sleep after the first work night) were significantly different from sleep after the first 2 workdays (p < .002). Tukey tests showed no significant differences in sleep quality between workdays and nights, with the exception of sleep after the third day compared to sleep after night shifts. However, significant differences were detected between off days and work nights (p < .01). ANOVA analysis showed borderline differences among perceived alertness during day shifts (p = .073) and significant differences among the hours of the shifts (p = .0005), especially when comparing the 2nd hour of the first day with the 10th hour of all the day shifts. There were no significant differences in perceived alertness during night work among the first, second, and third nights (p = .573), but there were significant differences comparing the times (2nd, 6th, 10th hour) of the night shifts (p < .001). The evaluation of sleep (duration and quality) and level of alertness have been extensively used in the literature as indicators of possible performance decrements at work. The results of this study show poorer sleep after and significantly decreased alertness during night work. Shifts of 12h are usually implemented for technical and economic reasons. These results point out the necessity of a careful trade-off between the financial and technical gains longer shifts might bring and the possible losses due to incidents or accidents from performance decrements during work.     

WORKING THE NIGHT SHIFT CAUSES INCREASED VASCULAR STRESS AND DELAYED RECOVERY IN YOUNG WOMEN

Shiftwork has been associated with elevated blood pressure (BP) and decreased heart-rate variability (HRV), factors that may increase the long-term risk of cardiovascular-related mortality and morbidity. This study explored the effect of shiftwork on dynamic changes in autonomic control of HRV (cardiac stress), systolic BP and diastolic BP, i.e., SBP and DBP (vascular stress), and recovery in the same subjects working different shifts. By studying the same subjects, the authors could reduce the effect of possible contribution of between-subject variation from genetic predisposition and environmental factors. The authors recruited 16 young female nurses working rotating shifts—day (08:00–16:00 h), evening (16:00–00:00 h), and night (00:00–08:00 h)—and 6 others working the regular day shift. Each nurse received simultaneous and repeated 48-h ambulatory electrocardiography and BP monitoring during their work day and the following off-duty day. Using a linear mixed-effect model to adjust for day shift, the results of the repeated-measurements and self-comparisons found significant shift differences in vascular stress. While working the night shift, the nurses showed significant increases in vascular stress, with increased SBP of 9.7 mm Hg. The changes of SBP and DBP seemed to peak during waking time at the same time on the day off as they did on the working day. Whereas HRV profiles usually returned to baseline level after each shift, the SBP and DBP of night-shift workers did not completely return to baseline levels the following off-duty day (p?<?.001). The authors concluded that although the nurses may recover from cardiac stress the first day off following a night shift, they do not completely recover from increases in vascular stress on that day. (Author correspondence: jdwang@ntu.edu.tw)     

Blood pressure dipping and salivary cortisol as markers of fatigue and sleep deprivation in staff anesthesiologists

Anesthesiologists often work extended duty shifts that result in acute and chronic sleep loss and circadian disruption. Stress caused by sleep deprivation, together with excessive workload could contribute to acute increases in blood pressure (BP) and sympathetic nervous system activity. Non-dipping pattern of BP is considered an additional risk factor for cardiovascular events and target organ damage. We hypothesized that there would be significant changes of cardiovascular parameters when comparing work on call during the 24-hour in-hospital shift (24-HD) versus ordinary working day (8-HD) combined with changes of dipping pattern and altered diurnal cortisol secretion, measured by salivary cortisol (SC). Following local Medical Ethics Committee approval, 12 out of 36 staff anesthesiologists (8 male, 4 female), 33-61 years old, participated in this study. Ambulatory BP monitor was used for noninvasive 24-hour ambulatory BP and heart rate (HR) monitoring. Each participant was monitored continuously during the 8-HD, as well as during the 24-HD. Saliva for analysis of cortisol levels was collected six times a day (at 8 am, 11 am, 2 pm, 5pm, 8pm, and 11 pm) both during 8-HD and on 24-HD. There was a significant decrease in number of diastolic dippers on call vs. diastolic dippers on ordinary working day (4/12 vs. 10/12, p=0.036), and non significant decrease of systolic dippers (3/12 vs. 7/12, p =0.214). There were no significant differences in SC values between 8-HD and 24-HD at all observed time points. However, the SC values measured during the night were markedly elevated on both days compared with reference values and the shapes of SC curves were altered. The lack of diastolic BP dipping could be more sensitive indicator of stress among staff anesthesiologists than systolic BP dipping. The shape of SC diurnal curve in terms of elevated night values could be another indicator of their chronic fatigue.     

IMPLEMENTATION OF 12-HOUR SHIFTS IN A BRAZILIAN PETROCHEMICAL PLANT: IMPACT ON SLEEP AND ALERTNESS

A recent worldwide trend in chemical and petrochemical industries is to extend the duration of shifts. Optimization of the labor force to reduce costs is one reason to increase the length of working time in a shift. Implementation of 12h shifts is a controversial decision for managers and scientists. Literature reviews show alertness is lower during the nighttime hours, and sleep duration is reduced and worse during the daytime. The main objective of this study was to evaluate the impacts of 12h shifts on alertness and sleep. To evaluate the duration and quality of sleep and alertness during work, 22 male shift workers on a continuous rotating schedule at a petrochemical plant completed activity logs and estimated alertness using analog 10-cm scales for 30 consecutive days, three times (at 2h, 6h, and 10h of the shift) every work shift. Statistical tests (analysis of variance [ANOVA] and Tukey) were performed to detect differences between workdays and off days. The shift schedule was 2 days/3 nights/4 off days, followed by 3 days/2 nights/5 off days, followed by 2 days/2 nights/5 off days. Sleep duration varied significantly (p <. 001) among the work shifts and off days. Comparing work nights, the shortest mean sleep occurred after the second night (mean = 311.4 minutes, SD = 101.7 minutes), followed by the third night (mean = 335.3 minutes, SD = 151.2 minutes). All but one shift (sleep after the first work night) were significantly different from sleep after the first 2 workdays (p <. 002). Tukey tests showed no significant differences in sleep quality between workdays and nights, with the exception of sleep after the third day compared to sleep after night shifts. However, significant differences were detected between off days and work nights (p <. 01). ANOVA analysis showed borderline differences among perceived alertness during day shifts (p =. 073) and significant differences among the hours of theshifts(p =. 0005), especially when comparing the 2nd hour of the first day with the 10th hour of all the day shifts. There were no significant differences in perceived alertness during night work among the first, second, and third nights (p =. 573), but there were significant differences comparing the times (2nd, 6th, 10th hour) of the night shifts (p ≤. 001). The evaluation of sleep (duration and quality) and level of alertness have been extensively used in the literature as indicators of possible performance decrements at work. The results of this study show poorer sleep after and significantly decreased alertness during night work. Shifts of 12h are usually implemented for technical and economic reasons. These results point out the necessity of a careful trade-off between the financial and technical gains longer shifts might bring and the possible losses due to incidents or accidents from performance decrements during work. (Chronobiology International, 17(4), 521–537, 2000)     

Sleepiness and recovery in schedule change and the eighty-four hour workweek

The aims were to evaluate sleepiness and recovery during a schedule change, and during an 84-hours workweek. The control group (16 men) stayed on a six-week schedule, whereas the intervention group (12 men) transferred to a seven-week schedule. Sleepiness was estimated, using the KSS-scale, four times during the first and the third night in the fifth or sixth shift week. Recovery was assessed through four estimations on days one, three and five during the week off. Statistical testing was carried out using repeated measurement ANOVA. Sleepiness at night was affected by night (F = 4.90, p < 0.05) and hour (F = 33.64, p < 0.001) in both groups. The intervention group was sleepier during the first recovery day compared to the control group (F = 4.02, p < 0.05). Analysis of the 84-hour-week showed an effect of night (F = 8.98, p < 0.05) and hour (F = 71.60, p < 0.001) on night work, and day (F = 22.49, p < 0.01) and hour (F = 6.66, p < 0.05) on recovery. Sleepiness was more pronounced on the first recovery day (F = 23.08, p < 0.01). The seven-week schedule showed no effect that differed from that of the control group on sleepiness during the night shift. After the 84-hour workweek the workers recovered in about three days. The new schedules may affect the first recovery day negatively.     

Effects of light intensity and restraint on dark-pulse-induced circadian phase shifting during subjective night in Syrian hamsters

Dark pulses presented on a background of constant light (LL) result in phase advances during midsubjective day and early subjective night, and phase delays during late subjective night, as shown in the dark-pulse phase response curve. In hamsters, the phase-shifting effects of dark pulses are thought to be mediated by increased activity, as previous studies have shown that restraining animals during dark pulses blocks the phase shifts observed in midsubjective day and late subjective night. This study focuses on dark-pulse-induced phase shifting during early subjective night, examining the influence of both LL intensity and restraint on the magnitude of these phase shifts. Syrian hamsters were maintained in LL of four different illumination levels (1, 10, 100, or 600 lux) and periodically presented with 6-h pulses (dark pulse alone, restraint alone, or dark pulse plus restraint) beginning at circadian time 11. Phase advances were observed in response to dark pulses alone, and the magnitude of these shifts was dependent on background illumination, with significantly larger advances seen under higher intensities. No relationship was found between the amount of activity displayed during dark pulses and phase shift magnitude. Six-hour periods of restraint resulted in phase delays, the magnitude of which was also dependent on background illumination. Restraining hamsters during dark pulses reduced the magnitude of phase advances, but the extent of this reduction could be predicted from the additive effects of the dark-pulse-alone and restraint-alone conditions. These results indicate that the phase-shifting effects of dark pulses during early subjective night are not mediated by behavioral activation and may instead reflect a mirror image of the phase-delaying effects of light pulses at this phase.     

Effects of work schedule and period of exposure on changes in urinary chromium and nickel excretion among rotating shift workers in a stainless-steel plant

ABSTRACT

We investigated the association between the period of exposure and changes in urinary excretion of chromium and nickel among rotating shift workers in a stainless-steel plant. The study participants were composed of two groups: the workers who were occupationally exposed to metals (“exposed group”) and those who were not occupationally exposed to metals (“unexposed group”). The exposed and unexposed groups consisted of 56 and 40 male rotating shift workers, respectively. Urine samples were collected immediately before and immediately after the day shift, evening shift, and night shift. Urinary chromium and nickel were measured using inductively coupled plasma mass spectrometry. To correct for variations in urine dilution, urinary metal concentrations were expressed as a ratio to urinary creatinine concentration. In the exposed group, post-shift urinary excretion of chromium was significantly higher than pre-shift excretion. However, although urinary chromium excretion clearly increased after the day and night shift [63% (p < .0001) and 87% (p < .0001), respectively], urinary chromium excretion after the evening shift was only slightly higher than that measured before the evening shift (8%, p = .028). Similar patterns were found for urinary nickel excretion (p = .0001, 0.20, and 0.18 for the day, evening, and night shifts, respectively). Non-uniform urinary excretion of metals between the day shift, evening shift, and night shift were observed in the exposed group; specifically, urinary metal excretion increased only slightly during the evening shift. In the unexposed group, no significant increase or decrease was found in median urinary chromium or nickel excretion (p= .63–0.87). Work shift-specific permissible exposure level would be necessary.     

Effects of Filtering Visual Short Wavelengths During Nocturnal Shiftwork on Sleep and Performance

Circadian phase resetting is sensitive to visual short wavelengths (450–480?nm). Selectively filtering this range of wavelengths may reduce circadian misalignment and sleep impairment during irregular light-dark schedules associated with shiftwork. We examined the effects of filtering short wavelengths (<480?nm) during night shifts on sleep and performance in nine nurses (five females and four males; mean age?±?SD: 31.3?±?4.6 yrs). Participants were randomized to receive filtered light (intervention) or standard indoor light (baseline) on night shifts. Nighttime sleep after two night shifts and daytime sleep in between two night shifts was assessed by polysomnography (PSG). In addition, salivary melatonin levels and alertness were assessed every 2?h on the first night shift of each study period and on the middle night of a run of three night shifts in each study period. Sleep and performance under baseline and intervention conditions were compared with daytime performance on the seventh day shift, and nighttime sleep following the seventh daytime shift (comparator). On the baseline night PSG, total sleep time (TST) (p?<?0.01) and sleep efficiency (p?=?0.01) were significantly decreased and intervening wake times (wake after sleep onset [WASO]) (p?=?0.04) were significantly increased in relation to the comparator night sleep. In contrast, under intervention, TST was increased by a mean of 40?min compared with baseline, WASO was reduced and sleep efficiency was increased to levels similar to the comparator night. Daytime sleep was significantly impaired under both baseline and intervention conditions. Salivary melatonin levels were significantly higher on the first (p?<?0.05) and middle (p?<?0.01) night shifts under intervention compared with baseline. Subjective sleepiness increased throughout the night under both conditions (p?<?0.01). However, reaction time and throughput on vigilance tests were similar to daytime performance under intervention but impaired under baseline on the first night shift. By the middle night shift, the difference in performance was no longer significant between day shift and either of the two night shift conditions, suggesting some adaptation to the night shift had occurred under baseline conditions. These results suggest that both daytime and nighttime sleep are adversely affected in rotating-shift workers and that filtering short wavelengths may be an approach to reduce sleep disruption and improve performance in rotating-shift workers. (Author correspondence: casper@lunenfeld.ca)     

Circadian temperature rhythms in clockwise and counter-clockwise rapidly rotating shift schedules

The purpose of this study was to examine the circadian temperature rhythm in clockwise (CW) and counter-clockwise (CCW) rapidly rotating shift schedules. Arguments against the CCW rotation of shifts are that they result in shortened sleep and promote greater disruption of circadian rhythms. The 3-week study included a week of day shifts (0800-1600) and 2 weeks of shiftwork. The CW 2-2-1 schedule rotated from two early mornings (0600-1400) to two evenings (1400-2200) to one midnight shift (2200-0600) allowing 24 hours off at each shift rotation and a 48-hour weekend. The CCW schedule rotated from two evenings to two early mornings to one midnight shifts allowing only 8 hours off at each shift rotation and an 80-hour weekend. Analysis of the 72-hr periods at the end of each workweek, including the midnight shifts and recovery periods during weeks 2 and 3 were compared to the same 72-hour period at the end of week 1 (baseline). A cosine function that fit the temperature curves by minimizing the sums of squares produced parameters that underwent analysis of covariance procedures. Significant differences were found between rotation conditions for amplitude and acrophase. An attenuation of amplitude and a delay in the acrophase was the found for the counter-clockwise condition. Features inherent in this schedule might explain these effects, particularly, the increased opportunity for "sleeping in" at the beginning of the week and an expanded (2-shift) workday at the end of the week.     

Exploring sleepiness and entrainment on permanent shift schedules in a physiologically based model

The effects of permanent shift work on entrainment and sleepiness are examined using a mathematical model that combines a model of sleep-wake switch in the brain with a model of the human circadian pacemaker entrained by light and nonphotic inputs. The model is applied to 8-hour permanent shift schedules to understand the basic mechanisms underlying changes of entrainment and sleepiness. Average sleepiness is shown to increase during the first days on the night and evening schedules, that is, shift start times between 0000 to 0700 h and 1500 to 2200 h, respectively. After the initial increase, sleepiness decreases and stabilizes via circadian re-entrainment to the cues provided by the shifts. The increase in sleepiness until entrainment is achieved is strongly correlated with the phase difference between a circadian oscillator entrained to the ambient light and one entrained to the shift schedule. The higher this phase difference, the larger the initial increase in sleepiness. When entrainment is achieved, sleepiness stabilizes and is the same for different shift onsets within the night or evening schedules. The simulations reveal the presence of a critical shift onset around 2300 h that separates schedules, leading to phase advance (night shifts) and phase delay (evening shifts) of the circadian pacemaker. Shifts starting around this time take longest to entrain and are expected to be the worst for long-term sleepiness and well-being of the workers. Surprisingly, we have found that the circadian pacemaker entrains faster to night schedules than to evening ones. This is explained by the longer photoperiod on night schedules compared to evening. In practice, this phenomenon is difficult to see due to days off on which workers switch to free sleep-wake activity. With weekends, the model predicts that entrainment is never achieved on evening and night schedules unless the workers follow the same sleep routine during weekends as during work days. Overall, the model supports experimental observations, providing new insights into the mechanisms and allowing the examination of conditions that are not accessible experimentally.     

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.     

Heart rate variability changes in business process outsourcing employees working in shifts

Background and Objectives

Irregular and poor quality sleep is common in business process outsourcing (BPO) employees due to continuous shift working. The influence of this on the cardiac autonomic activity was investigated by the spectral analysis of heart rate variability (HRV).

Methods

36 night shift BPO employees (working from 22:00 to 06:00h) and 36 age and sex matched day shift BPO employees (working from 08:00 to 16:00h) were recruited for the study. Five minute electrocardiogram (ECG) was recorded in all the subjects. Heart rate variability was analyzed by fast Fourier transformation using RMS Vagus HRV software. The results were analyzed using Mann Whitney U test, Student t-test, Wilcoxon signed rank test and were expressed as mean ± SD.

Results

Sleepiness was significantly higher among night shift workers as measured by Epworth Sleepiness Scale (p<0.001). Night shift BPO employees were found to have a trend towards lower values of vagal parameters - HF power (ms²), and higher values of sympathovagal parameters like LF Power (ms²) and the LF/HF power (%) suggesting decreased vagal activity and sympathetic over activity, when compared to day shift employees. However, HRV parameters did not vary significantly between the day shift employees and night shift workers baseline values, and also within the night shift group.

Interpretation and Conclusion

Night shift working increased the heart rate and shifted the sympathovagal balance towards sympathetic dominance and decreased vagal parameters of HRV. This is an indicator of unfavorable change in the myocardial system, and thus shows increased risk of cardiovascular disease among the night shift employees.     

Metabolic Syndrome in Permanent Night Workers

Night and shift work might be risk factors for metabolic and cardiovascular disorders due to interference with diet, circadian metabolic rhythms, and lifestyle. The relationship between permanent night work and metabolic and cardiovascular risk factors was explored in a retrospective longitudinal study of workers employed in a large municipal enterprise in charge of street cleaning and domestic waste collection. All subjects who had worked night shifts between 1976 and 2007 as hand sweepers, motor sweepers, and delivery tricar drivers were compared with subjects who always worked the same jobs but on day shifts. From the periodical medical surveillance files, we identified 488 male workers who had been examined on average five times (minimum 2, maximum 14) during the study period, for a total of 2,328 medical examinations; 157 always had worked day shifts, 12 always the night shift, and 319 both (initially day and subsequently night shifts). Their age ranged from 22 to 62 yrs, and work experience varied from 1 to 28 yrs. Lifestyle habits (smoking, alcohol consumption), body mass index, serum glucose, total cholesterol, tryglicerides, hepatic enzymes, blood pressure, resting electrocardiogram, diabetes, coronary heart disease, hypertension, and related drugs were taken into consideration for the analysis. We used generalized estimating equations (GEE) models (exchangeable correlation matrix) to analyze the relationship between night work and health effects while accounting for within‐subject correlations and adjusting for study period, job, age, and lifestyle variables. As a whole, night workers smoked more and had significantly higher BMI, serum total cholesterol, and triglycerides than day workers. Both the inter‐individual comparison between day and night workers and the intra‐individual comparison among the workers, who were day workers at the beginning of their employment and later became night workers, showed a significant increase in BMI, total cholesterol, and tryglicerides associated with night work. No consistent effect was seen on fasting glucose, hepatic enzymes, and blood pressure, whereas a higher incidence of coronary heart disease was recorded in night workers.     

Metabolic syndrome in permanent night workers

Night and shift work might be risk factors for metabolic and cardiovascular disorders due to interference with diet, circadian metabolic rhythms, and lifestyle. The relationship between permanent night work and metabolic and cardiovascular risk factors was explored in a retrospective longitudinal study of workers employed in a large municipal enterprise in charge of street cleaning and domestic waste collection. All subjects who had worked night shifts between 1976 and 2007 as hand sweepers, motor sweepers, and delivery tricar drivers were compared with subjects who always worked the same jobs but on day shifts. From the periodical medical surveillance files, we identified 488 male workers who had been examined on average five times (minimum 2, maximum 14) during the study period, for a total of 2,328 medical examinations; 157 always had worked day shifts, 12 always the night shift, and 319 both (initially day and subsequently night shifts). Their age ranged from 22 to 62 yrs, and work experience varied from 1 to 28 yrs. Lifestyle habits (smoking, alcohol consumption), body mass index, serum glucose, total cholesterol, tryglicerides, hepatic enzymes, blood pressure, resting electrocardiogram, diabetes, coronary heart disease, hypertension, and related drugs were taken into consideration for the analysis. We used generalized estimating equations (GEE) models (exchangeable correlation matrix) to analyze the relationship between night work and health effects while accounting for within-subject correlations and adjusting for study period, job, age, and lifestyle variables. As a whole, night workers smoked more and had significantly higher BMI, serum total cholesterol, and triglycerides than day workers. Both the inter-individual comparison between day and night workers and the intra-individual comparison among the workers, who were day workers at the beginning of their employment and later became night workers, showed a significant increase in BMI, total cholesterol, and tryglicerides associated with night work. No consistent effect was seen on fasting glucose, hepatic enzymes, and blood pressure, whereas a higher incidence of coronary heart disease was recorded in night workers.     

Some peculiarities of the physiological validity of shift work schedules for the crews of floating oil drilling platforms

Observations of the physiological status changes in the crews of floating oil drilling platforms during 7-day and 15-day shifts revealed that in subjects working the two shift schedules, the pattern of changes in the parameters of the central nervous system, circulation, muscle strength and endurance during the first 7 days corresponded to a physiological response to experienced challenge. In those working a 15-day schedule, the differences between the current and original status of the investigated physiological functions started to increase from day nine onwards, reaching a maximum on day fifteen. The alterations were most pronounced in subjects exposed predominantly to psychoemotional challenges during their labour. The evidence accumulated in the present study prompted the recommendation of a 7-day work-and-rest schedule as more reasonable physiologically for the crews of floating oil drilling platforms.     

Changes in the diurnal rhythms of cortisol,melatonin, and testosterone after 2, 4, and 7 consecutive night shifts in male police officers

Night work is associated with a large range of acute health problems and possibly also health consequences in the long run. Yet, only very few field studies specifically investigate the effects of consecutive night shift on key physiological regulatory systems. In this field study, we investigated the effects of consecutive night shifts on three hormones, melatonin, cortisol, and testosterone, among police officers at work. More specifically, the aim was to investigate how the diurnal rhythms of melatonin, cortisol, and testosterone responded to two, four, and seven consecutive night shifts and a corresponding number of days for recovery. The study was part of the “In the Middle of the Night” project and included 73 male police officers from five different police districts. The participants were exposed to three intervention conditions: “2+2”: two consecutive night shifts followed by two consecutive day recovery days; “4+4”: four consecutive night shifts followed by four consecutive recovery days; “7+7”: seven consecutive night shifts followed by seven consecutive recovery days. On the last day with night shift and the last recovery day in each intervention, the participants collected saliva samples every 4th hour when awake. The diurnal rhythms of melatonin, cortisol, and testosterone were all affected differently by an increasing number of consecutive night shifts: the amplitude of the melatonin rhythm was suppressed by 4.9% per day (95% CI 1.4–8.2% per day; p = 0.006). The diurnal rhythm of cortisol phase was delayed with an increasing number of night shifts by 33 min/day (95% CI 18–48 min per day; p ≤ 0.001), but did not show any changes in amplitude. For the diurnal rhythm of testosterone, there was no effect of the number of consecutive night shifts and the diurnal rhythm completely followed the sleep/wake cycle. We found that there were no differences in the rhythms of melatonin, cortisol, and testosterone after 2, 4, and 7 recovery days, respectively. In conclusion, we found signs of desynchronization in terms of suppressed amplitude of melatonin and phase delay of salivary cortisol as a consequence of the increasing number of consecutive night shifts among police officers at work. Lack of synchronization has been suggested as a possible mechanism linking night work to disease, but this remains to be determined.