The effect of the number of consecutive night shifts on diurnal rhythms in cortisol, melatonin and heart rate variability (HRV): a systematic review of field studies

Night and shift work and incidence of physician-diagnosed sleep disorders in nursing staff: A prospective cohort study

BACKGROUND

Epidemiological studies provide evidence for an association between shift work and sleep problems but often lack precise exposure and outcome data.

OBJECTIVE

To investigate the risk of first-time physician-diagnosed sleep disorder in nursing staff using register-based data of shift work and health outcomes.

DESIGN

A prospective cohort study with a 4.5-year follow-up.

PARTICIPANTS

25,639 healthcare employees (nurses including midwives, nursing assistants, and related care professions) employed for at least six months between 2012 and 2016 by Region Stockholm were included.

METHODS

Information on hour-by-hour and day-by-day working hours was obtained from a computerised employee register. Physician-diagnosed sleep disorders (N = 326) were obtained from an outpatient register from January 2013 to June 2017. Discrete time proportional hazards models were used to estimate hazard ratios (HR) adjusting for age, sex, country of birth and profession.

RESULTS

An increased risk of physician-diagnosed sleep disorder was seen among those who, during the preceding six months, only or frequently (>66 times) worked night shifts compared to those who did not work nights (HR 1.70, 95 % CI 1.17-2.43 and HR 1.77, 95 % CI 1.21-2.50 respectively). The associations were supported by a dose-response pattern (p = 0.0006). Among those who work night shifts, the risk associated with 9-12 times of three or more consecutive nights was of borderline statistical significance (HR 1.66, 95 % CI 0.98-2.81). Frequently (>39 times the last six months) having quick returns from night shifts (<28 h) showed an almost 2-fold increased risk of physician-diagnosed sleep disorder compared to those who had few (<8 times in the last six months) quick returns from night shifts (HR 1.89, 95 % CI 1.05-3.52). Quick returns from afternoon shifts in non-night workers (<11 h) did not significantly increase the risk of physician-diagnosed sleep disorder.

CONCLUSION

The results indicate that intensive night shift work, especially frequent and consecutive night shifts, is associated with an increased risk of physician-diagnosed sleep disorder in nursing staff. This study raises awareness of the need to acknowledge objective in addition to subjective health outcomes in relation to shift work.

Sleep duration and quality in permanent night work: an observational field study

PURPOSE

Permanent night workers conceivably show better adaptation of circadian rhythms to night work than shift workers and therefore better possibilities of obtaining sufficient sleep of good quality after night shifts. We investigated the effect of night shifts including number of consecutive shifts on sleep among self-selected permanent night workers, and studied if the effect of night shifts differed between morning and evening types and compared with 3-shift workers.

METHODS

The study population included 90 permanent night workers followed for 14 days (warehouse workers, 1228 observation days, 80% males). For comparison, we included 70 3-shift workers followed for 26 days (police officers, 1774 observation days, 100% men). Total sleep time (TST), primary sleep duration (PSD), and sleep efficiency were assessed by actigraphy. Measures of sleep quality and diurnal type were self-reported.

RESULTS

Among permanent night workers, TST, PSD, difficulties falling asleep, disturbed sleep, and the number of awakenings decreased after night shifts compared with days without night work. Sleep efficiency, difficulties awakening, and non-refreshing sleep increased. More consecutive night shifts were associated with shorter TST and PSD. Sleep outcomes did not differ by diurnal type. Permanent night workers had fewer awakenings after night shifts than 3-shift workers, but no other differences were observed.

CONCLUSION

This study does not provide evidence that supports recommendation of permanent night work to reduce adverse effects of night shifts on sleep. A limited number of consecutive night shifts is recommended to reduce accumulation of sleep debt.

Update: factors influencing heart rate variability-a narrative review

Objective

Heart rate variability (HRV) is an important non-invasive marker for the assessment of an organism's autonomic physiological regulatory pathways. Lower HRV has been shown to correlate with increased mortality. HRV is influenced by various factors or diseases. The aim of this narrative review is to describe the current state of knowledge on factors influencing HRV and their significance for interpretation.

Methods

The narrative review only included reviews, meta-analyses, and cohort studies which were published until 2021. HRV confounders were grouped into four categories (non-influenceable physiological factors, diseases, influenceable lifestyle factors and external factors).

Results

The review found that HRV was decreased not only in non-influenceable physiological factors (e.g., age, gender, ethnicity) but also in connection with various number of acute and chronic diseases (e.g., psychiatric diseases, myocardial infarction, heart failure), influenceable lifestyle factors (e.g., alcohol abuse, overweight, physical activity), and external factors (e.g., heat, noise, shift work, harmful- and hazardous substances).

Conclusion

In order to improve the quality of HRV studies and to ensure accurate interpretation, it is recommended that confounders be taken into account in future diagnostic measurements or measurements in the workplace (e.g., as part of health promotion measures) in order to counteract data bias.

Altered coordination between sleep timing and cortisol profiles in night working female hospital employees

BACKGROUND

Cortisol typically peaks in the morning after waking up and declines throughout the day, reaching its lowest levels during nighttime sleep. Shift work can cause misalignment between cortisol levels and sleep-wake timing. We analyzed this misalignment in female shift workers focusing on the timing and extent of these changes.

METHODS

We conducted a cross-sectional study involving 68 shift workers (aged 37 ± 10 years) and 21 non-shift workers (aged 45 ± 10 years) from a hospital. Shift workers were monitored through two day shifts and three night shifts, whereas non-shift workers were monitored during two day shifts. Each participant collected six to eight saliva samples (depending on their shift type) and provided sleep timing information, which was recorded via polysomnography and sleep diaries. Generalized additive mixed models were used to estimate shift-specific differences in cortisol smooth curves. Summary measures calculated for the cortisol smooth curves included cortisol awakening response, peak-to-bed slope, and total output.

RESULTS

Between shift workers and non-shift workers, we observed similar diurnal cortisol profiles with a steep negative diurnal slope during day shifts. In shift workers on night shifts, a flattened U-shaped cortisol profile after the post-awakening maximum was observed, with a peak-to-bed slope close to zero. When comparing night to day shifts in the group of shift workers, mean cortisol levels were lower between 42 and 56 minutes and 1.8-11.9 hours after waking up, and higher between 14.9 and 22 hours after waking up.

CONCLUSION

Our findings indicate altered cortisol profiles in female hospital employees on night shifts. Specifically, cortisol levels were lower at night when higher levels would typically be necessary for work activities, and higher at bedtime after a night shift, when levels should normally be low.

Guideline for the application of heart rate and heart rate variability in occupational medicine and occupational health science

This updated guideline replaces the "Guideline for the application of heart rate and heart rate variability in occupational medicine and occupational health science" first published in 2014. Based on the older version of the guideline, the authors have reviewed and evaluated the findings on the use of heart rate (HR) and heart rate variability (HRV) that have been published in the meantime and incorporated them into a new version of this guideline.This guideline was developed for application in clinical practice and research purposes in the fields of occupational medicine and occupational science to complement evaluation procedures with respect to exposure and risk assessment at the workplace by the use of objective physiological workload indicators. In addition, HRV is also suitable for assessing the state of health and for monitoring the progress of illnesses and preventive medical measures. It gives an overview of factors influencing the regulation of the HR and HRV at rest and during work. It further illustrates methods for measuring and analyzing these parameters under standardized laboratory and real workload conditions, areas of application as well as the quality control procedures to be followed during the recording and evaluation of HR and HRV.

Move the night way: how can physical activity facilitate adaptation to shift work?

Shift work, involving night work, leads to impaired sleep, cognition, health and wellbeing, and an increased risk of occupational incidents. Current countermeasures include circadian adaptation to phase shift circadian biomarkers. However, evidence of real-world circadian adaptation is found primarily in occupations where light exposure is readily controlled. Despite this, non-photic adaptation to shift work remains under researched. Other markers of shift work adaptation exist (e.g., improvements in cognition and wellbeing outcomes) but are relatively unexplored. Timeframes for shift work adaptation involve changes which occur over a block of shifts, or over a shift working career. We propose an additional shift work adaptation timeframe exists which encompasses acute within shift changes in markers of adaptation. We also propose that physical activity might be an accessible and cost-effective countermeasure that could influence multiple markers of adaptation across three timeframes (Within Shift, Within Block, Within Work-span). Finally, practical considerations for shift workers, shift work industries and future research are identified.

Circadian Adaptation of Melatonin and Cortisol in Police Officers Working Rotating Shifts

Misalignment of behavior and circadian rhythms due to night work can impair sleep and waking function. While both simulated and field-based studies suggest that circadian adaptation to a nocturnal schedule is slow, the rates of adaptation in real-world shift-work conditions are still largely unknown. The aim of this study was to evaluate the extent of adaptation of 24-h rhythms with 6-sulfatoxymelatonin (aMT6s) and cortisol in police officers working rotating shifts, with a special attention to night shifts. A total of 76 police officers (20 women; aged 32 ± 5.4 years, mean ± SD) from the province of Quebec, Canada, participated in a field study during their 28- or 35-day work cycle. Urine samples were collected for ~32 h before a series of day, evening, and night shifts to assess circadian phase. Before day, evening, and night shifts, 60%-89% of officers were adapted to a day schedule based on aMT6 rhythms, and 71%-78% were adapted based on cortisol rhythms. To further quantify the rate of circadian adaptation to night shifts, initial and final phases were determined in a subset of 37 officers with suitable rhythms for both hormones before and after 3-8 consecutive shifts (median = 7). Data were analyzed with circular and linear mixed-effects models. After night shifts, 30% and 24% of officers were adapted to a night-oriented schedule for aMT6s and cortisol, respectively. Significantly larger phase-delay shifts (aMT6s: -7.3 ± 0.9 h; cortisol: -6.3 ± 0.8 h) were observed in police officers who adapted to night shifts than in non-adapted officers (aMT6s: 0.8 ± 0.9 h; cortisol: 0.2 ± 1.1 h). Consistent with prior research, our results from both urinary aMT6s and cortisol midpoints indicate that a large proportion of police officers remained in a state of circadian misalignment following a series of night shifts in dim-light working environments.

Prevalence of Reproductive Health Issues among US Female Law Enforcement Officers

Reproductive health is a considerable concern among US female law enforcement officers (LEOs). Miscarriage and preterm birth rates are significantly higher in women firefighters than published US averages. Since law enforcement and firefighting share occupational conditions and practices, adverse birth outcomes were hypothesized to be greater in female law enforcement officers (LEOs) than the US averages. Occupational hazards may place pregnant LEOs at a higher risk for complicated pregnancies and adverse birth outcomes. This study quantified pregnancy outcomes in female LEOs using a cross-sectional survey and compared them to US averages and large prospective studies. The participants (N = 162, 72.2% aged 31-49, 85.2% Caucasian) averaged 2.5 ± 1.4 pregnancies. Stress (59.1%) and shiftwork (59.8%) were the most common reported exposures. Miscarriage and preterm birth rates were 19.1% and 16.4%, respectively. Miscarriages were significantly greater among participants compared to prospective studies [χ2 (1, N = 911,971) = 20.51, p < 0.001]. Female LEOs of childbearing age should receive education about potential reproductive health hazards and take precautions against them. Moreover, policymakers, human resources, and healthcare providers should understand how law enforcement work might affect maternal health.

A Blue-Enriched Light Intervention Counteracts the Alertness Decrement Among Mine Workers on Extended 12-Hour Night Shift Periods

OBJECTIVE

The aim of the study is to assess whether a blue-enriched light intervention improves nocturnal alertness and daytime sleep of night workers.

METHODS

Thirteen miners performing 12-hour night shifts for 12 consecutive nights were exposed to a baseline and a blue-enriched light condition. All subjects wore an actigraph and completed a Psychomotor Vigilance Task at the beginning and at the end of each shift. Data were analyzed with linear mixed models.

RESULTS

In the blue-enriched light condition, the daily increase in median reaction time (RT), mean RT, slowest 10% of RT, and fastest 10% of RT was lower than that observed in the baseline condition between day 1 and 12 ( P ≤ 0.05).

CONCLUSIONS

The addition of blue-enriched light during a long period of extended night shifts counteracts most of the daily decline in nocturnal alertness observed in the standard lighting condition, irrespectively of sleep duration and sleep efficiency.

Morphofunctional State and Circadian Rhythms of the Liver of Female Rats under the Influence of Chronic Alcohol Intoxication and Constant Lighting

A separate and combined effect of constant illumination and chronic alcohol intoxication (CAI) on diurnal dynamics of micromorphometric parameters of hepatocytes in female Wistar rats and p53, Ki-67, PER2, BMAL1, and ADH5 expression in these cells were studied. The increase in apoptotic activity and proliferation in all animals under the action of chronodestructors is shown. All experimental animals showed a decrease in BMAL1 expression and increase in PER2 expression; ADH5 is overexpressed under the influence of ethanol. Circadian rhythms (CRs) of BMAL1, PER2, p53, and Ki-67 expression persist in all groups, except combined action of chronodestructors, and ADH5 CRs persist in all groups—thus, these rhythms in females are quite stable. CRs of the hepatocyte nuclei area are preserved in all the studied groups, although they undergo a significant shift. At the same time, the CRs of the hepatocyte area are destroyed under the action of light, both independently and in combination with CAI, and the CR of the nuclear-cytoplasmic ratio (NCR) is destroyed by exposure to CAI. It can be assumed that CRs of the hepatocyte area are significantly affected by dark deprivation and NCR rhythm is sensitive to ethanol consumption, while the stability of studied genes’ expression rhythms at separate influences of studied chronodestructors is maintained by yet unknown adaptation mechanisms. It is necessary to note that, according to our previous studies of male rats, rat females show significantly greater stability of the studied CRs.

Night work, chronotype and cortisol at awakening in female hospital employees

To examine the effect of night shift on salivary cortisol at awakening (C1), 30 min later (C2), and on the cortisol awakening response (CAR, the difference between C2 and C1). We compared shift and non-shift workers with a focus on the impact of worker chronotype. Our study included 66 shift-working females (mean age = 37.3 years, SD = 10.2) and 21 non-shift working females (mean age = 47.0 years, SD = 8.9). The shift workers collected their saliva samples at C1 and C2 on each two consecutive day shifts and night shifts. Non-shift workers collected their samples on two consecutive day shifts. We applied linear mixed-effects models (LMM) to determine the effect of night shift on CAR and log-transformed C1 and C2 levels. LMMs were stratified by chronotype group. Compared to non-shift workers, shift workers before day shifts (i.e. after night sleep) showed lower cortisol at C1 (exp [Formula: see text]=0.58, 95% CI 0.42, 0.81) but not at C2. In shift workers, the CARs after night shifts (i.e. after day sleep) were lower compared to CARs before day shifts ([Formula: see text]= - 11.07, 95% CI - 15.64, - 6.50). This effect was most pronounced in early chronotypes (early: [Formula: see text]= - 16.61, 95% CI - 27.87, - 5.35; intermediate: [Formula: see text]= - 11.82, 95% CI - 18.35, - 5.29; late: [Formula: see text]= - 6.27, 95% CI - 14.28, 1.74). Chronotype did not modify the association between night shift and CAR. In our population of shift workers, there was a mismatch between time of waking up and their natural cortisol peak at waking up (CAR) both during day and night shift duties.

Shift and night work during pregnancy and preterm birth-a cohort study of Swedish health care employees

BACKGROUND

Previous studies of preterm birth (PTB) concerning night work have been inconclusive and partly limited by imprecise data on working schedules. This study investigated the risk of PTB in relation to detailed, registry-based data on working hours.

METHODS

In a register-based prospective cohort study, we identified 4970 singleton births with information on PTB from the Swedish Medical Birth Register of health care employees in Stockholm. Day-by-day information on working hours 2008-16 was obtained from a computerized employee register. Odds ratios (ORs) of PTB according to work hour characteristics were analysed by logistic regression adjusted for mother's age, stature, body mass index (BMI), parity, smoking habits, education, profession and country of birth.

RESULTS

There was an increased risk of PTB among those who frequently worked night shifts (>25 times) [OR, 1.62; 95% confidence interval (CI), 1.03-2.53] and who ever worked ≥3 consecutive night shifts (OR, 1.43; 95% CI, 1.03-1.99) during the first trimester. Frequently (> 8 times) working 3 or more consecutive nights, and frequently (>18 times) having quick returns from night shifts (<28 h) during the first trimester showed 3-4 fold increased risk of PTB. Moreover, working frequent (>20 times) long shifts (≥10 h) (OR 1.63; 95% CI, 1.07-2.49) during the first trimester and working any Week >40 h (OR 2.05; 95% CI, 1.31-3.22) during the third trimester were associated with PTB.

CONCLUSIONS

In this cohort of Swedish health care employees with registry-based data on working hours, night work, especially working frequent consecutive nights, and quick returns from night shifts during the first trimester were associated with increased risk of PTB among pregnant women.

Chronotype-specific Sleep in Two Versus Four Consecutive Shifts

The study aimed to explore chronotype-specific effects of two versus four consecutive morning or night shifts on sleep-wake behavior. Sleep debt and social jetlag (a behavioral proxy of circadian misalignment) were estimated from sleep diary data collected for 5 weeks in a within-subject field study of 30 rotating night shift workers (29.9 ± 7.3 years, 60% female). Mixed models were used to examine whether effects of shift sequence length on sleep are dependent on chronotype, testing the interaction between sequence length (two vs. four) and chronotype (determined from sleep diaries). Analyses of two versus four morning shifts showed no significant interaction effects with chronotype. In contrast, increasing the number of night shifts from two to four increased sleep debt in early chronotypes, but decreased sleep debt in late types, with no change in intermediate ones. In early types, the higher sleep debt was due to accumulated sleep loss over four night shifts. In late types, sleep duration did not increase over the course of four night shifts, so that adaptation is unlikely to explain the observed lower sleep debt. Late types instead had increased sleep debt after two night shifts, which was carried over from two preceding morning shifts in this schedule. Including naps did not change the findings. Social jetlag was unaffected by the number of consecutive night shifts. Our results suggest that consecutive night shifts should be limited in early types. For other chronotypes, working four night shifts might be a beneficial alternative to working two morning and two night shifts. Studies should record shift sequences in rotating schedules.

The potential of using hair cortisol to measure chronic stress in occupational healthcare; a scoping review

OBJECTIVES

Workplace-based selective prevention of mental health problems currently relies on subjective evaluation of stress complaints. Hair cortisol captures chronic stress responses and could be a promising biomarker for the early identification of mental health problems. The objective was to provide an overview of the state-of-the-art knowledge on the practical value of hair cortisol in the occupational setting.

METHODS

We performed a scoping review of cross-sectional and longitudinal studies in PubMed, Embase, and PsycINFO up to November 2019 assessing the relations of hair cortisol with work-related stressors, perceived stress, and mental health outcomes in healthy workers.

RESULTS

We found five longitudinal studies, of which two observed an increase in work-related stressors to be associated with higher hair cortisol, one found a relation with lower hair cortisol and one did not find a relationship. Findings of cross-sectional studies were also mixed. The one available longitudinal study regarding mental health showed that hair cortisol was not related to depressive symptoms.

CONCLUSIONS

Hair cortisol measurement within occupational health research is still in its early stage and more longitudinal studies are urgently needed to clarify its relationship with work-related stressors and perceived stress before hair cortisol can be used to identify workers at risk for mental health problems.

A Blue-Enriched, Increased Intensity Light Intervention to Improve Alertness and Performance in Rotating Night Shift Workers in an Operational Setting

PURPOSE

This study examined the efficacy of a lighting intervention that increased both light intensity and short-wavelength (blue) light content to improve alertness, performance and mood in night shift workers in a chemical plant.

PATIENTS AND METHODS

During rostered night shifts, 28 workers (46.0±10.8 years; 27 male) were exposed to two light conditions each for two consecutive nights (~19:00-07:00 h) in a counterbalanced repeated measures design: traditional-spectrum lighting set at pre-study levels (43 lux, 4000 K) versus higher intensity, blue-enriched lighting (106 lux, 17,000 K), equating to a 4.5-fold increase in melanopic illuminance (24 to 108 melanopic illuminance). Participants completed the Karolinska Sleepiness Scale, subjective mood ratings, and the Psychomotor Vigilance Task (PVT) every 2-4 hours during the night shift.

RESULTS

A significant main effect of time indicated KSS, PVT mean reaction time, number of PVT lapses (reaction times > 500 ms) and subjective tension, misery and depression worsened over the course of the night shift (p<0.05). Percentage changes in KSS (p<0.05, partial η²=0.14) and PVT mean reaction time (p<0.05, partial η²=0.19) and lapses (p<0.05, partial η²=0.17) in the middle and end of night shift, expressed relative to start of shift, were significantly improved during the lighting intervention compared to the traditional lighting condition. Self-reported mood did not significantly differ between conditions (p>0.05).

CONCLUSION

Our findings, showing improvements in alertness and performance with exposure to blue-enriched, increased intensity light, provide support for light to be used as a countermeasure for impaired alertness in night shift work settings.

The Role of Light Sensitivity and Intrinsic Circadian Period in Predicting Individual Circadian Timing

There is large interindividual variability in circadian timing, which is underestimated by mathematical models of the circadian clock. Interindividual differences in timing have traditionally been modeled by changing the intrinsic circadian period, but recent findings reveal an additional potential source of variability: large interindividual differences in light sensitivity. Using an established model of the human circadian clock with real-world light recordings, we investigated whether changes in light sensitivity parameters or intrinsic circadian period could capture variability in circadian timing between and within individuals. Healthy participants (n = 12, aged 18-26 years) underwent continuous light monitoring for 3 weeks (Actiwatch Spectrum). Salivary dim-light melatonin onset (DLMO) was measured each week. Using the recorded light patterns, a sensitivity analysis for predicted DLMO times was performed, varying 3 model parameters within physiological ranges: (1) a parameter determining the steepness of the dose-response curve to light (p), (2) a parameter determining the shape of the phase-response curve to light (K), and (3) the intrinsic circadian period (tau). These parameters were then fitted to obtain optimal predictions of the three DLMO times for each individual. The sensitivity analysis showed that the range of variation in the average predicted DLMO times across participants was 0.65 h for p, 4.28 h for K, and 3.26 h for tau. The default model predicted the DLMO times with a mean absolute error of 1.02 h, whereas fitting all 3 parameters reduced the mean absolute error to 0.28 h. Fitting the parameters independently, we found mean absolute errors of 0.83 h for p, 0.53 h for K, and 0.42 h for tau. Fitting p and K together reduced the mean absolute error to 0.44 h. Light sensitivity parameters captured similar variability in phase compared with intrinsic circadian period, indicating they are viable targets for individualizing circadian phase predictions. Future prospective work is needed that uses measures of light sensitivity to validate this approach.

Measuring psychological and physiological stress in emergency clinicians

BACKGROUND

Evidence regarding stress, team structure and decision-making has been used to inform efficacious team composition and deployment. There have been limited attempts to establish the relationship between psychological stress with physiological data within professional environments. The current study explored measures of psychological and physiological stress in Australian emergency practitioners.

METHODS

Thirty-seven staff in an Australian emergency department completed an online survey assessing freedom to make decisions, social support, and psychological job demands. Seven participants provided saliva samples three times daily for seven days (valid n=141 samples). Cortisol levels of the samples were analysed using competitive enzyme immunoassay kits, and α-amylase using kinetic enzyme assay kits.

RESULTS

Years of emergency experience was positively associated with freedom to make decisions, and social support was negatively correlated with psychological demand. No consistent pattern was observed between cortisol level and reported psychological demand, decision freedom or social support. Physical activity was not reflected in elevated α-amylase. Diurnal variation of cortisol and α-amylase was not affected by shiftwork.

CONCLUSIONS

The data supports the case for using multiple assessments to measure stress. While the psychological data is consistent with previous findings, there are possible disparities between psychological reports and physical indicators of stress.

Heart rate variability and hematological parameters in pregnant women

Background

There are few researches on hematological parameters (hemoglobin, red cell distribution width [RDW], white blood cells [WBCs], mean platelets volume [MPV], and heart rate variability [HRV]). There are no published data on this concept (HRV and hematological parameters) during pregnancy.

Methods

A cross‐sectional study was conducted at Saad Abul Ela hospital in Khartoum, Sudan during the period of July to August 2018. Pregnant women with singleton, a live baby, were enrolled in this study. Clinical history and examination were performed. HRV (autonomic modulation) was assessed using time and frequency domain HRV indices.

Results

One hundred and five pregnant women were enrolled. The median (quartile) of the age, parity, and gestational age was 30.0 (25.0‐35.0) years, 1.0 (0‐3.0), and 38.0 (32.0‐39.0) weeks, respectively. While there were positive correlations between hemoglobin and low frequency (LF), RDW and high frequency (HF), WBCs and HF Norm, WBCs and LF/HF, MPV and HF Norm, LF Norm and LF/HF, there was no significant correlation between the hematological (hemoglobin, WBCs, RDW, and MPV) and HRV parameters. Linear regression analysis showed no significant association between age, parity, gestational age, body mass index, hemoglobin, RDW, and HRV variables. The Log₁₀ WBCs were negatively associated with Log₁₀ HF (ms²/Hz). MPV was positively associated with LF Norm and negatively associated with HF Norm.

Conclusion

The study failed to show significant associations between age, parity, gestational age, hemoglobin, RDW, and HRV variables. The WBCs were negatively associated with HF. MPV was positively associated with LF Norm, and it was negatively associated with HF Norm.

Insomnia, excessive daytime sleepiness, anxiety, depression and socioeconomic status among customer service employees in Canada

OBJECTIVE

It is the first study investigating deeply symptoms of neuropsychiatric diseases among a large population of customer service employees (n=1238, 640 females and 598 males). The study's goals were document presence of sleep disorders, anxiety and depression among customer service advisors and determine the influence of the socioeconomic status (pSES), duration in position and full-time or part-time shift on the diseases above.

METHODS

Linear regressions and ANOVA with a Tukey multiple comparisons of means was performed to analyze correlation and differences between citizens, international students and immigrants in their pSES and neuropsychiatric diseases.

RESULTS

Customer service employees (578 Canadians, 264 immigrants and 358 international students) are in majority undergraduate students (286 men and 289 females) with a high school degree (280 men and 308 women). They work full-time (560 men and 548 women) and are single (420 men and 560 women). Among customer service advisors, the time spent as an advisor was an excellent predictor of insomnia, sleepiness and anxiety (respectively with R2=91,83%, R2=81,23% and R2=87,46%) but a moderate predictor of depression (R2=69,14%). The pSES was a moderate predictor of sleep disorders (respectively R2=62,04% for insomnia and R2=53,62% for sleepiness) and strongly associated with anxiety and depression (R2=82,95% for anxiety and R2=89,77% for depression).

DISCUSSION

Insomnia, sleepiness and anxiety are more prevalent for full-time employees (higher for immigrants and international students compared to Canadians) compared with part-time employees, while depression was similarly higher for Canadian and immigrants compared to international students. Regarding full-time employees, symptoms of insomnia, anxiety and depression were higher for men compared to women. Regarding part-time employees, symptoms of insomnia and sleepiness were higher for women compared to men. Employees working full-time with rotating shifts are more exposed to insomnia, sleepiness and anxiety than employees working part-time. More research is needed to understand mental health of customer service employees regardless of their area and it is worthy of interest to study the link between sleep disorders and mood disorders with work conditions. Here some practical suggestions are made to reduce neuropsychiatric disorders for customer service employees or to at least mitigate the work burden on their brains.

Pain complaints are associated with quick returns and insomnia among Norwegian nurses, but do not differ between shift workers and day only workers

PURPOSE

To determine whether common work schedule characteristics among Norwegian nurses were associated with subjective pain complaints.

METHODS

A cross-sectional study in a sample of 1585 nurses, part of the longitudinal questionnaire-based cohort project 'Survey of Shift work, Sleep and Health' (SUSSH). Pain from six regions were assessed: 'headache', 'neck/shoulder/upper back', 'upper extremities', 'lower back', 'lower extremities', and 'abdomen'. Logistic and negative binomial regression (adjusted for age, sex, percentage of full-time equivalent, marital status and children living at home) were conducted where work schedule, number of night shifts last year, number of quick returns (QR) last year (< 11 h between shifts) and insomnia were predictors of localized pain, widespread pain and number of pain sites.

RESULTS

Localized pain, widespread pain and number of pain sites were associated with insomnia (OR 2.06, 95% CI 1.66-2.55, OR 2.14, 95% CI 1.47-3.09, IRR 1.70, 95% CI 1.51-1.91, respectively). Work schedule and number of night shifts worked last year were not associated with any of the three pain measures. Number of QRs worked last year tended to be associated with number of pain sites.

CONCLUSION

The study did not support the hypothesis that non-daytime work schedules are associated with pain complaints. Neither was there support for the hypothesis linking number of night shifts, or the number of QRs, to pain complaints. Future studies should aim to determine the association between QRs and pain in more detail. Pain complaints were associated with insomnia.

Shift Work and Heart Rate Variability Coherence: Pilot Study Among Nurses

This study used ambient heart rate monitoring among health care workers to determine whether a novel measure of heart rate variability (HRV), as well as sleep disturbances, fatigue, or cognitive performance differed among non-rotating night shift nurses relative to those working permanent day shifts. Continuous ambulatory HRV monitoring was performed among night nurses (n = 11), and a comparison group of permanent day nurses (n = 7), over a 36-h period coinciding with the last two 12-h shifts of each participant's work week. Symptoms and psychomotor vigilance were assessed at the end of the ambient HRV monitoring period, and no differences between shifts were observed. Day nurses exhibited an increase in hourly mean HRV coherence ratios during their sleep period, suggesting a circadian pattern of cardiorespiratory phase coupling, whereas night nurses had no increase in HRV coherence ratios during their sleep period. The HRV coherence patterns were similar to high frequency HRV power among nurses on the same shift. To the authors knowledge, this study was the first to quantify patterns of the HRV coherence ratio among shiftworkers in a non-experimental (work/home) setting. The results suggest a pattern of autonomic dysregulation among night workers during their sleep period relative to those working day shifts. The HRV coherence ratio may serve as a novel indicator of HRV dysregulation among shift workers.

Night work and sick leave during pregnancy: a national register-based within-worker cohort study

Objective

The aim of our study was to investigate the acute effect of night work during pregnancy on the risk of calling in sick the following day using register-based information and the workers as their own controls.

Methods

Using the payroll-based national Danish Working Hour Database, including all public hospital employees in Denmark, we identified 9799 pregnant women with ≥1 day shift and ≥1 night shift and ≥1 day of sick leave during the first 32 pregnancy weeks from January 2007 to December 2013. We performed fixed effects logistic regression, that is, within-worker comparisons, of the risk of sick leave of any duration starting within 24 hours after night shifts of different length versus day shifts.

Results

Most of the participants were nurses (64%) or physicians (16%). We found an increased relative risk of sick leave following night shifts compared with day shifts during all pregnancy trimesters. The risk was highest for night shifts lasting >12 hours (OR 1.37, 95% CI 1.15 to 1.63 for nurses; OR 1.87, 95% CI 1.69 to 2.08 for physicians) and among women aged >35 years (OR 1.42, 95% CI 1.24 to 1.63).

Conclusion

Among Danish public hospital employees night shifts during pregnancy, especially shifts longer than 12 hours, increased the risk of calling in sick the following day independent of personal factors and time-invariant confounders in all pregnancy trimesters.

Exposure to working-hour characteristics and short sickness absence in hospital workers: A case-crossover study using objective data

INTRODUCTION

Shift work characteristics, such as the number of night shifts or quick returns, are linked to disturbed sleep and greater work-life conflict, but little is known about their association with short sickness absences. Studies utilizing objective working-hour characteristic data can provide knowledge on specific shift work characteristics that may associate with sick leave. We investigated the association between working-hour characteristics in shift work and the incidence of short (1-3 days) sickness absences.

PARTICIPANTS AND METHODS

The individual-level data were collected from the employers' electronic working time records of the Finnish Public Sector study. The final analytical sample was restricted to the first incidence of short sickness absence (1-3 days) from January 1, 2008 to the end of 2015. We studied employees with shift work contracts (n = 12 156) and day work contracts (n = 6225). Of these, 89% were female workers, with a mean age of 37.1 years, and 12% worked part-time. We calculated type of shift (morning, day, evening, and night), quick returns (< 11 h between two work shifts), length of work shift and weekly working time. We utilized case-crossover study design to compare the working-hour characteristics of the 28 days preceding sickness absence (exposure window) and those of the 28 days before the exposure window (control window), using conditional logistic regression models for odds ratios with 95% Confidence Intervals (95%CI).

RESULTS

Exposure to ≥ 2, and especially ≥ 4 consecutive night shifts associated with an increased likelihood of short sickness absence (OR 1.24, 95%CI 1.12-1.38 and OR 1.54, 95%CI 1.10-2.15, respectively) among shift workers, whereas a high number (> 25%) of evening shifts and having ≥ 2 consecutive evening shifts associated with lower odds of sickness absence. Over 40-hour weeks (OR 1.29, 95%CI 1.20-1.39), over 48-hour weeks (OR 1.24, 95%CI 1.01-1.54) and quick returns (OR 1.02, 95%CI 1.01-1.02) increased the likelihood of sickness absence. Having only a few (0-1 or 2-3) quick returns over 28 days decreased the likelihood of sickness absence (ORs 0.46 and 0.67), whereas having ≥ 5 quick returns over 28 days increased it (OR 1.88, 95%CI 1.76-1.99). These associations were similar among both shift and day workers.

CONCLUSIONS

Long working hours, several consecutive night shifts and quick returns increase the risk of short sickness absence. These working-hour characteristics should be avoided in shift scheduling to minimize sickness absence and increased costs for the employer.

Night Shift Work and Risk of Breast Cancer

PURPOSE OF REVIEW

Night work is increasingly common and a necessity in certain sectors of the modern 24-h society. The embedded exposure to light-at-night, which suppresses the nocturnal hormone melatonin with oncostatic properties and circadian disruption, i.e., misalignment between internal and external night and between cells and organs, are suggested as main mechanisms involved in carcinogenesis. In 2007, the International Agency for Research on Cancer (IARC) classified shift work that involves circadian disruption as probably carcinogenic to humans based on limited evidence from eight epidemiologic studies on breast cancer, in addition to sufficient evidence from animal experiments. The aim of this review is a critical update of the IARC evaluation, including subsequent and the most recent epidemiologic evidence on breast cancer risk after night work.

RECENT FINDINGS

After 2007, in total nine new case-control studies, one case-cohort study, and eight cohort studies are published, which triples the number of studies. Further, two previous cohorts have been updated with extended follow-up. The assessment of night shift work is different in all of the 26 existing studies. There is some evidence that high number of consecutive night shifts has impact on the extent of circadian disruption, and thereby increased breast cancer risk, but this information is missing in almost all cohort studies. This in combination with short-term follow-up of aging cohorts may explain why some cohort studies may have null findings. The more recent case-control studies have contributed interesting results concerning breast cancer subtypes in relation to both menopausal status and different hormonal subtypes. The large differences in definitions of both exposure and outcome may contribute to the observed heterogeneity of results from studies of night work and breast cancer, which overall points in the direction of an increased breast cancer risk, in particular after over 20 years of night shifts. Overall, there is a tendency of increased risk of breast cancer either after over 20 years of night shift or after shorter periods with many consecutive shifts. More epidemiologic research using standardized definitions of night work metrics and breast cancer subtypes as well as other cancers is needed in order to improve the epidemiologic evidence in combination with animal models of night work. Also, evidence-based preventive interventions are needed.

Temporal dynamics of circadian phase shifting response to consecutive night shifts in healthcare workers: role of light-dark exposure

KEY POINTS

Shift work is highly prevalent and is associated with significant adverse health impacts. There is substantial inter-individual variability in the way the circadian clock responds to changing shift cycles. The mechanisms underlying this variability are not well understood. We tested the hypothesis that light-dark exposure is a significant contributor to this variability; when combined with diurnal preference, the relative timing of light exposure accounted for 71% of individual variability in circadian phase response to night shift work. These results will drive development of personalised approaches to manage circadian disruption among shift workers and other vulnerable populations to potentially reduce the increased risk of disease in these populations.

ABSTRACT

Night shift workers show highly variable rates of circadian adaptation. This study examined the relationship between light exposure patterns and the magnitude of circadian phase resetting in response to night shift work. In 21 participants (nursing and medical staff in an intensive care unit) circadian phase was measured using 6-sulphatoxymelatonin at baseline (day/evening shifts or days off) and after 3-4 consecutive night shifts. Daily light exposure was examined relative to individual circadian phase to quantify light intensity in the phase delay and phase advance portions of the light phase response curve (PRC). There was substantial inter-individual variability in the direction and magnitude of phase shift after three or four consecutive night shifts (mean phase delay -1:08 ± 1:31 h; range -3:43 h delay to +3:07 h phase advance). The relative difference in the distribution of light relative to the PRC combined with diurnal preference accounted for 71% of the variability in phase shift. Regression analysis incorporating these factors estimated phase shift to within ±60 min in 85% of participants. No participants met criteria for partial adaptation to night work after three or four consecutive night shifts. Our findings provide evidence that the phase resetting that does occur is based on individual light exposure patterns relative to an individual's baseline circadian phase. Thus, a 'one size fits all' approach to promoting adaptation to shift work using light therapy, implemented without knowledge of circadian phase, may not be efficacious for all individuals.

Melatonin in Apples and Juice: Inhibition of Browning and Microorganism Growth in Apple Juice

Synthetic melatonin (N-acetyl-5-methoxytryptamine, MT) is popular in the US and Asian markets as a health supplement. Here, we identified a naturally occurring melatonin source in apple juice. Melatonin was present in all 18 apple cultivars tested. The highest melatonin level of the edible part of apple was detected in the apple peel. The melatonin content in 'Fuji' apple juice is comparable to the level of its flesh. Melatonin was consumed during the process of juicing due to its interaction with the oxidants. Melatonin addition significantly reduced the juice color change to brown (browning). The mechanism is that melatonin scavenges the free radicals, which was indicated by the ASBT analysis; therefore, inhibiting the conversion of o-diphenolic compounds into quinones. Most importantly, melatonin exhibited powerful anti-microorganism activity in juice. The exact mechanisms of this action are currently unknown. These effects of melatonin can preserve the quality and prolong the shelf life of apple juice. The results provide valuable information regarding commerciall apple juice processing and storage.

Maternal Heart Rate Variability during the First Stage of Labor

Labor necessitates continuous adjustments of cardiac autonomic reflexes by alternate activation of the sympathetic and parasympathetic nervous systems. The division of the autonomic nervous system (ANS) that predominates during the first stage of labor is unclear and needs to be further investigated. The study aimed to compare heart rate variability (HRV) in pregnant women in the third trimester with those during the first stage of labor. We conducted a case-control study at Saad Abul Ela Maternity Hospital, Khartoum, Sudan. Forty-five women with singleton, live neonates in the first stage of labor and 45 women in the third trimester (but not in labor) were enrolled as case and control groups, respectively. Data on the medical history, obstetrics history, and clinical examinations that were performed in all of the studied women were obtained using prearranged questionnaires. Cardiac autonomic modulation (CAM) of the heart was examined in both groups based on time and frequency domain HRV indices. There were no significant differences in age, parity, body mass index, and hemoglobin levels between the two groups. Pregnant women in labor had significantly higher LnSDNN, LnRMSSD, LnTP, LnVLF, LnLF, LnHF, LF Norm, and LnLF/HF ratio, but lower HF Norm compared with controls (P < 0.001). These findings remained unchanged when possible confounders were controlled for using regression analysis. Our findings suggest a significant increase in indictors of sympathetic CAM, namely LF Norm and LnLF/HF, during labor. Sympathetic hypertonia associated with labor is unlikely to increase the risk of cardiac events because sympathetic CAM simultaneously increases with global HRV. Increased HRV during labor may be explained by parasympathetic activation as indicated by higher LnHF and LnRMSSD at the time of delivery.

Cortisol Levels and Autonomic Control of Heart Rate in Healthy Subjects

Introduction: There is an increase in level of stress in the general population because of the social, personal and professional demands. Currently, there are only simple tools that can safely measure this stress such as levels of cortisol and heart rate variability (HRV). Objective: To analyze the relationship between salivary cortisol and the cardiac autonomic modulation. Methods: A total of fifty-one male and female subjects between 18 and 40 years old were evaluated. Saliva collection was achieved for the salivary cortisol dosage. The collection was performed through the SalivetteR tube. After this collection, the median cortisol levels (0.24 ug/dl) were analyzed and the volunteers were divided into two groups: i) cortisol below the mediane ii) cortisol above the median. After this division, each group consisted of 25 volunteers and then was verified the following information: age, gender, weight, height, body mass index (BMI), blood pressure. Shortly thereafter was assessment of cardiac autonomic modulation por meio da HRV. The Polar RS800cx heart rate receiver was placed on the chest of the volunteers, in the vicinity of the distal third of the sternum. The volunteers were instructed to remain in rest with spontaneous breathing in dorsal position for 20 minutes. HRV analysis included geometric, time and frequency domain indices. Results: There were no statistical differences for the two groups regarding systolic and diastolic blood pressure, heart rate, RR intervals or linear and frequency indices for the volunteers. In addition, also there was no correlation the cortisol with the analyzed variables (SAP, p=0.460; DAP, p = 0.270; HR, p = 0.360; RR, p = 0.380; SDNN, p = 0.510; rMSSD, p = 0.660; pNN50, p = 0.820; RRtri, p = 0.170; TINN, p = 0.470; SD1, p = 0.650; SD2, p = 0.500; LF [ms2], p = 0.880; LF [nu], p = 0.970; HF [ms2], p = 0.870; HF [nu], p = 0.960; LF/HF, p = 0.380 Conclusion: Heart rate variability autonomic control was unchanged in healthy subjects with physiological distribution of salivary cortisol levels. There was no association between normal salivary cortisol and resting autonomic regulation of heart rate.

Night shift and rotating shift in association with sleep problems, burnout and minor mental disorder in male and female employees

OBJECTIVES

Shift work is associated with adverse physical and psychological health outcomes. However, the independent health effects of night work and rotating shift on workers' sleep and mental health risks and the potential gender differences have not been fully evaluated.

METHODS

We used data from a nationwide survey of representative employees of Taiwan in 2013, consisting of 16 440 employees. Participants reported their work shift patterns 1 week prior to the survey, which were classified into the four following shift types: fixed day, rotating day, fixed night and rotating night shifts. Also obtained were self-reported sleep duration, presence of insomnia, burnout and mental disorder assessed by the Brief Symptom Rating Scale.

RESULTS

Among all shift types, workers with fixed night shifts were found to have the shortest duration of sleep, highest level of burnout score, and highest prevalence of insomnia and minor mental disorders. Gender-stratified regression analyses with adjustment of age, education and psychosocial work conditions showed that both in male and female workers, fixed night shifts were associated with greater risks for short sleep duration (<7 hours per day) and insomnia. In female workers, fixed night shifts were also associated with increased risks for burnout and mental disorders, but after adjusting for insomnia, the associations between fixed night shifts and poor mental health were no longer significant.

CONCLUSIONS

The findings of this study suggested that a fixed night shift was associated with greater risks for sleep and mental health problems, and the associations might be mediated by sleep disturbance.

Acute effects of different light spectra on simulated night-shift work without circadian alignment

Short-wavelength and short-wavelength-enhanced light have a strong impact on night-time working performance, subjective feelings of alertness and circadian physiology. In the present study, we investigated acute effects of white light sources with varied reduced portions of short wavelengths on cognitive and visual performance, mood and cardiac output.Thirty-one healthy subjects were investigated in a balanced cross-over design under three light spectra in a simulated night-shift paradigm without circadian adaptation.Exposure to the light spectrum with the largest attenuation of short wavelengths reduced heart rate and increased vagal cardiac parameters during the night compared to the other two light spectra without deleterious effects on sustained attention, working memory and subjective alertness. In addition, colour discrimination capability was significantly decreased under this light source.To our knowledge, the present study for the first time demonstrates that polychromatic white light with reduced short wavelengths, fulfilling current lighting standards for indoor illumination, may have a positive impact on cardiac physiology of night-shift workers without detrimental consequences for cognitive performance and alertness.