Melatonin, sleep, and shift work adaptation

Association of psychosocial factors at work with fertility and menstrual disorders: A systematic review

OBJECTIVES

This systematic review aimed to assess the association between psychosocial factors in the workplace and menstrual abnormalities or fertility, focusing on literature implementing a prospective cohort design.

METHODS

We searched MEDLINE, EMBASE, PsycINFO, PsycARTICLES, and Japan Medical Abstracts Society electronic databases for studies published from inception to February 26, 2020, and updated the search in PubMed on May 29, 2024. Inclusion criteria were (P) adult female workers (over 18 years old), (E) presence of adverse psychosocial factors at work, (C) absence of adverse psychosocial factors at work, and (O) any menstrual cycle disorders, menstrual-related symptoms, or fertility issues. Prospective cohort studies were included. The included studies were summarized descriptively.

RESULTS

Database searching yielded 14,238 abstracts, with nine studies meeting the inclusion criteria. Outcomes included fertility (n = 5), irregular menstrual cycle (n = 1), early menopause (n = 1), endometriosis (n = 1), and serum hormones (n = 1). Study findings included that women with high job demands and low job control were less likely to conceive, and working over 40 h per week and frequent heavy lifting, and rotating night shift work increased the risk of earlier menopause. Studies on night shift/rotating work and fertility outcomes showed no significant differences.

CONCLUSION

This review underscores the insufficient high-level evidence regarding the association of psychosocial factors at work with fertility and menstrual disorders, emphasizing the necessity for future well-designed studies.

Disrupted Circadian Rhythms and Substance Use Disorders: A Narrative Review

Substance use disorder is a major global health concern, with a high prevalence among adolescents and young adults. The most common substances of abuse include alcohol, marijuana, cocaine, nicotine, and opiates. Evidence suggests that a mismatch between contemporary lifestyle and environmental demands leads to disrupted circadian rhythms that impair optimal physiological and behavioral function, which can increase the vulnerability to develop substance use disorder and related problems. The circadian system plays an important role in regulating the sleep-wake cycle and reward processing, both of which directly affect substance abuse. Distorted substance use can have a reciprocal effect on the circadian system by influencing circadian clock gene expression. Considering the detrimental health consequences and profound societal impact of substance use disorder, it is crucial to comprehend its complex association with circadian rhythms, which can pave the way for the generation of novel chronotherapeutic treatment approaches. In this narrative review, we have explored the potential contributions of disrupted circadian rhythms and sleep on use and relapse of different substances of abuse. The involvement of circadian clock genes with drug reward pathways is discussed, along with the potential research areas that can be explored to minimize disordered substance use by improving circadian hygiene.

The effects of sleep restriction during abstinence on oxycodone seeking: Sex-dependent moderating effects of behavioral and hypothalamic-pituitary-adrenal axis-related phenotypes

During opioid use and abstinence, sleep disturbances are common and are thought to exacerbate drug craving. In this study, we tested the hypothesis that sleep restriction during abstinence from oxycodone self-administration would increase drug seeking during extinction and footshock reinstatement tests. We also performed behavioral phenotyping to determine if individual variation in responses to stressors and/or pain are associated with oxycodone seeking during abstinence, as stress, pain and sleep disturbance are often co-occurring phenomena. Sleep restriction during abstinence did not have selective effects on oxycodone seeking for either sex in extinction and footshock reinstatement tests. Some phenotypes were associated with drug seeking; these associations differed by sex and type of drug seeking assessment. In female rats, pain-related phenotypes were related to high levels of drug seeking during the initial extinction session. In male rats, lower anxiety-like behavior in the open field was associated with greater drug seeking, although this effect was lost when correcting for oxycodone intake. Adrenal sensitivity prior to oxycodone exposure was positively associated with footshock reinstatement in females. This work identifies sex-dependent relationships between HPA axis function and opioid seeking, indicating that HPA axis function could be a therapeutic target for the treatment of opioid use disorder, with tailored approaches based on sex. Sleep disturbance during abstinence did not appear to be a major contributing factor to opioid seeking.

Influence of psychosocial factors at work on the non-departmental security officers of the National Guard of the Russian Federation

   An analysis of modern research has shown insufficient study of the labor factors that influence the development of various functional states of non-departmental security officers which allow to develop the recommendations to improve their psychological safety.   The aim of the study. To identify and to describe psychosocial factors at work in relation to the general functional state of the body, stress and performance of non-departmental security officers.   Methods. We used the General Nordic Questionnaire for Psychological and Social Factors at Work (QPSNordic), psychophysiological testing using “Psychophysiologist” device, M. Lüscher color preference test, multivariate statistical methods. The study involved 74 non-departmental security officers of the Arkhangelsk region.   Results. The general functional state of the body, stress and performance, measured by objective and projective methods, are differentially interconnected with psychosocial factors at work. The general functional state of the body is related with the personal attitude to the work performed; stress and performance – with factors of social support, organizational culture and work requirements. The general functional state of non-departmental security officers is favorably influenced by such factors as understanding the goals of the work performed and the expected results, satisfaction with the quality of work and labor safety. Insufficient ability to maintain good relations with the team unfavorably influences the general functional state of the officers. The factors of work intensity include one-type tasks, tight schedule, increased alertness during work and greater precision in movements. Risk factors are associated with strict working hours and insufficient attention of the manage-ment to the opinion and interests of subordinates. At the same time, the environmental resource is the possibility of realizing professional motives and demonstrating mastery in work, as well as a favorable organizational culture.

Gynecologic problems and healthcare behavior by shift patterns in Korean nursing staff

We aimed to evaluate the clinical impact of shift patterns at work on gynecologic problems and the healthcare behavior of Korean nursing staff. We conducted a web-based survey for over two weeks in September 2021, involving female nursing staff, including nurses, nurses' aides, and nursing assistants, working in five medical centers. The questionnaire included 40 questions on baseline characteristics, working information, and experiences with gynecologic problems and medical approaches. Overall, 885 nursing staffs participated in the survey, of the 1,904 who received the invitation with an online link of the survey. The response rate was 46.5%. Among the participants responding to all questions, 569 (64.4%) worked two or three shifts and 305 (34.5%) worked full-time. In women rotating two or three-shift patterns, irregular menstrual cycles (21.6% vs. 13.8%, p = 0.005), abnormal menstrual cycles (40.9% vs. 33.8%, p = 0.038), and dysmenorrhea (48.0% vs. 38.4%, p = 0.006) were more frequent than in those who worked full-time. The experience of visiting gynecologic clinics (47.5% vs. 44.1%, p = 0.332) and treating gynecologic conditions (33.4% vs. 29.3%, p = 0.211) did not differ according to the working patterns. However, diagnosis of gynecologic diseases was more frequent in women working full-time (36.4% vs. 29.7%, p = 0.043). The rates of screening (76.1% vs. 57.8%, p<0.001) and human papillomavirus vaccination (55.7% vs. 39.9%, p<0.001) for cervical cancer prevention were higher in women working full-time than in two-three shifts. This study showed that rotating shift work may be related to an increase in gynecologic problems and a decrease in cancer prevention activity among female nursing staff.

The relationships of shift work, hair cortisol concentration and dyslipidaemia: a cohort study in China

BACKGROUND

Currently, cardiovascular disease is the leading cause of death, and dyslipidaemia is an independent and modifiable major risk factor. Previous studies on shift work with dyslipidaemia and hair cortisol concentration (HCC) have yielded conflicting results. The aim of this study was to clarify the association between shift work, dyslipidaemia, and HCC. We further explored the mediating effect of HCC.

METHODS

In this cohort study, baseline data were collected from participants in May 2013. The cohort included 2170 participants- 1348 shift workers and 822 non-shift workers- who were followed up for 6 years with four questionnaire surveys from July 2014, October 2015, and May to December 2019. Hair samples were collected from 340 participants during the baseline period for HCC testing with an automated radioimmunoassay. Dyslipidaemia was defined using the National Cholesterol Education Program Adult Treatment Panel III diagnostic criteria.

RESULTS

Shift workers had a higher risk of dyslipidaemia than workers on the fixed day shift (two-shift RR = 1.408, 95% CI: 1.102-1.798; three-shift RR = 1.478, 95% CI: 1.134-1.926; four-shift RR = 1.589, 95% CI: 1.253-2.015). Additionally, shift workers had higher HCC levels than fixed day shift workers, with geometric mean concentration (GMC) ± geometric standard difference (GSD) = 2.625 ± 2.012 ng/g, two-shift GMC ± GSD = 3.487 ± 1.930 ng/g, three-shift GMC ± GSD = 2.994 ± 1.813 ng/g, and four-shift GMC ± GSD = 3.143 ± 1.720 ng/g. High HCC was associated with a high incidence of dyslipidaemia. After controlling for confounding factors, this study showed that HCC played a role in mediating dyslipidaemia in shift workers and accounted for 16.24% of the effect.

CONCLUSIONS

Shift work was linked to increased risk of dyslipidaemia compared with fixed day shift work. Higher HCC was associated with a higher prevalence of dyslipidaemia. HCC had a significant mediating effect on dyslipidaemia in shift workers.

Work Conditions of Italian Nurses and Their Related Risk Factors: A Cohort Investigatory Study

(1) Background: Nursing is a satisfying employment pathway, as nurses preserve lives, but it is also considered one of the most stressful care professions. Nursing is a lifesaving and highly satisfying profession, yet it is considered one of the most stressful occupations. This study aimed to assess differences in anxiety, depression and stress states among nurses according to gender, work history, shift and body mass index (BMI) characteristics. (2) Methods: An online questionnaire was addressed to all Italian nurses during May 2022, investigating anxiety, depression and stress conditions according to the Depression, Anxiety and Stress Scale-21 Items (DASS-21) and sampling characteristics, such as sex, work experience, shift and BMI values. (3) Results: A total of 408 Italian nurses answered the questionnaire. Significant differences between the following were reported: anxiety levels and work experience, since nurses employed over 6 years reported higher anxiety levels than their younger colleagues (p = 0.035); depression levels and sex (p = 0.017), as females reported higher depression levels than males; and also between depression levels and BMI levels (p = 0.003), as 5.90% of overweight and 2.50% of obese participants reported extremely severe depression. By considering stress levels according to sampling characteristics, significant differences were registered according to BMI levels (p < 0.001), as overweight subjects reported higher stress levels (7.40%) than the other subgroups. Finally, significant associations were recorded between anxiety, depression and stress conditions with sex, work experience, shift and BMI. (4) Conclusions: The data were in agreement with the current literature, indicating that nurses might take care not only of their patients but also of themselves, in both the physical and mental aspects.

Post-traumatic stress disorder prevalence and sleep quality in fire victims and rescue workers in southern Brazil: a cross-sectional study

OBJECTIVES

This survey was conducted to evaluate the prevalence of post-traumatic stress disorder (PTSD) and the sleep quality in victims and rescue team of the third deadliest nightclub fire in the world.

STUDY DESIGN

A cross-sectional study.

METHODS

Participants were victims and rescue workers exposed to a fire at a nightclub, which occurred in January 2013 in Southern Brazil. The Pittsburgh Sleep Quality Index (PSQI), composed of seven subjective sleep variables (including daytime dysfunction), and PTSD Checklist - Civilian version (PCL-C) were applied to all people who sought medical attention at the local reference center in the first year after the event. Comprehensive information was obtained concerning sociodemographic factors, health status, and sleep complaints.

RESULTS

A total of 370 individuals, 190 victims and 180 rescue workers, were included. Participants were 70% male, with an average age of 29 years. The prevalence of PTSD was 31.9%, ranging from 24.4% for rescue workers to 38.9% for victims. The prevalence of poor sleep quality was 65.9%, ranging from 56.1% for rescue workers to 75.3% for victims. Most of the participants with PTSD (91.5%) had PSQI scores >5 (poor sleepers), against 54.0% of the non-PTSD individuals. All seven PSQI subscores showed significant differences between PTSD and non-PTSD individuals, especially daytime dysfunction. Sex, shift work, previous psychiatric disease, and sleep quality remained associated with PTSD in adjusted models, with a prevalence ratio (95% CI) of 1.76 (1.28-2.43) in females, 1.73 (1.17-2.55) in shift workers, 1.36 (1.03-1.80) in individuals with psychiatric disease history, and 5.42 (2.55-11.52) in poor sleepers.

CONCLUSIONS

The presence of daytime dysfunction increased by at least tenfold the prevalence of PTSD in this sample. Considering that daytime dysfunction was shown to be strongly associated with PTSD, sleep-related issues should be addressed in the assessment of individuals exposed to traumatic events, both victims and rescuers. Factors like shift work and female sex were also associated with PTSD, especially among victims.

Impact of sleep timing on attention, sleepiness, and sleep quality among real-life night shift workers with shift work disorder: a cross-over clinical trial

STUDY OBJECTIVES

To examine the effect of sleep timing intervention on sleep quality, attention, and sleepiness at work among night shift workers with shift work disorder.

METHODS

We recruited 60 real-life night shift workers through advertisements to participate this cross-over clinical trial. Shift work disorder was confirmed with interview and sleep log. Participants were designated to follow evening sleep (15:00-23:00) and morning sleep (09:00-17:00) schedules in a randomized order. Chronotype was confirmed by the Munich Chronotype Questionnaire. Sleep behaviors and light exposure were recorded using actigraphy. Outcome measures were sleepiness evaluated by the Karolinska Sleepiness Scale, sleep quality evaluated by the Pittsburgh Sleep Quality Index, and attention performance assessed with psychomotor vigilance test. Differences in outcome between the morning and evening sleep schedules were compared using repeated measures ANOVA.

RESULTS

The participants slept for longer durations during evening sleep schedules compared with morning sleep schedules. Lower sleepiness scores, higher sleep quality, and shorter reaction times and less lapse numbers in the psychomotor vigilance test were observed for participants during evening sleep schedules than morning sleep schedules after adjustment for light exposure and sleep duration. Significant interaction effects were observed for reaction time and lapse number between chronotype and sleep schedule, where the differences between sleep schedules were most prominent among those with late chronotypes.

CONCLUSIONS

It is recommended that night shift workers with shift work disorder arrange to sleep in the evening instead of the morning for better sleep and attention performance, especially those with late chronotypes.

TRIAL REGISTRATION

Sleep Schedule Intervention Study Among Night Shift Workers, https://clinicaltrials.gov/ct2/show/NCT04160572, ClinicalTrials.gov Identifier: NTC04160572.

Sleep status of psychiatric nurses: A survey from China

Aim

Our study aimed to evaluate the sleep status of psychiatric nurses in Chinese population and analyse the influencing factors.

Design

Cross‐sectional, correlation design with logistic regression analysis.

Methods

We investigated 1,044 psychiatric nurses from seven psychiatric hospitals in China. Pittsburgh Sleep Quality Index and Maslach Burnout Inventory General Survey were used as main measures.

Results

The average Pittsburgh Sleep Quality Index score of 1,044 psychiatric nurses was 7.00 ± 3.59, and 38.63% of nurses had a total Pittsburgh Sleep Quality Index score >7. Our study found that middle‐night shift nurses had poor sleep quality and sleep disorders are positively correlated with emotional exhaustion and cynical disregard for job burnout. Middle‐night shift nurses showed 1.586 times more likely to suffer from sleep disorders than those non‐middle‐night shift. The higher the score of emotional exhaustion, the greater the risk of sleep disorders.

A multimodal analysis of physical activity, sleep, and work shift in nurses with wearable sensor data

Night shift workers are often associated with circadian misalignment and physical discomfort, which may lead to burnout and decreased work performance. Moreover, the irregular work hours can lead to significant negative health outcomes such as poor eating habits, smoking, and being sedentary more often. This paper uses commercial wearable sensors to explore correlates and differences in the level of physical activity, sleep, and circadian misalignment indicators among day shift nurses and night shift nurses. We identify which self-reported assessments of affect, life satisfaction, and sleep quality, are associated with physiological and behavioral signals captured by wearable sensors. The results using data collected from 113 nurses in a large hospital setting, over a period of 10 weeks, indicate that night shift nurses are more sedentary, and report lower levels of life satisfaction than day-shift nurses. Moreover, night shift nurses report poorer sleep quality, which may be correlated with challenges in their attempts to fall asleep on off-days.

Association between night-shift work and level of melatonin: systematic review and meta-analysis

BACKGROUNDS

Night-shift workers are exposed to nocturnal light and are more prone to circadian rhythm disorders. Although night-shift work is thought to be associated with the decrease in melatonin secretion, studies have shown inconsistent results.

METHODS

This systematic review and meta-analysis studied the association between night-shift work and melatonin levels. Pubmed and Embase databases were used for literature searching. The pooled standardized mean differences (SMDs) and 95% confidence intervals (CIs) were used to compare the differences between night-shift workers and the controls.

RESULTS

Thirty-three studies reported in 25 articles (1845 night-shift workers and 3414 controls, mean age 45.12 years) were included after a systematic literature review. Data of circulating melatonin levels and its metabolites, 6-sulfatoxymelatonin (aMT6s) in urine were collected for meta-analysis. The results showed that the first morning-void aMT6s level in night-shift workers was significantly lower than in day workers (SMD = -0.101, 95% CI = -0.179 to -0.022, P = 0.012). The level of mean 24-h urinary aMT6s was lower in night-shift workers than day workers (SMD: -0.264, 95% CI: -0.473 to -0.056, P = 0.013). Among fixed night-shift workers, the level of circulating melatonin, as well as first morning-void aMT6s was lower than that of day workers.

CONCLUSION

Our findings indicate that experience of night-shift work is associated with suppression of melatonin production, especially among fixed night-shift workers.

Metabolic implications of circadian disruption

Circadian rhythms are generated by the circadian clock, a self-sustained internal timing system that exhibits 24-h rhythms in the body. In mammals, circadian rhythms are driven by a central clock located in suprachiasmatic nucleus and various peripheral clocks located in different tissues and organs of the body. Many cellular, behavioral, and physiological processes are regulated by the circadian clock in coordination with environmental cues. The process of metabolism is also under circadian regulation. Loss of synchronization between the internal clock and environmental zeitgebers results in disruption of the circadian rhythms that seriously impacts metabolic homeostasis leading to changed eating behavior, altered glucose and lipid metabolism, and weight gain. This in turn augments the risk of having various cardio-metabolic disorders such as obesity, diabetes, metabolic syndrome, and cardiovascular disease. This review sheds light on circadian rhythms and their role in metabolism with the identification of gaps in the current knowledge that remain to be explored in these fields. In this review, the molecular mechanisms underlying circadian rhythms have been elaborated first. Then, the focus has been kept on explaining the physiological significance of circadian rhythms in regulating metabolism. Finally, the implications for metabolism when these rhythms are disrupted due to genetic mutations or social and occupational needs enforced by modern lifestyle have been discussed.

Light Exposure during Days with Night, Outdoor, and Indoor Work

OBJECTIVE

To assess light exposure during days with indoor, outdoor, and night work and days off work.

METHODS

Light intensity was continuously recorded for 7 days across the year among indoor (n = 170), outdoor (n = 151), and night workers (n = 188) in Denmark (55-56°N) equipped with a personal light recorder. White light intensity, duration above 80, 1000, and 2500 lux, and proportion of red, green, and blue light was depicted by time of the day and season for work days and days off work.

RESULTS

Indoor workers' average light exposure only intermittently exceeded 1000 lux during daytime working hours in summer and never in winter. During daytime working hours, most outdoor workers exceeded 2500 lux in summer and 1000 lux in winter. Night workers spent on average 10-50 min >80 lux when working night shifts. During days off work, indoor and night workers were exposed to higher light intensities than during work days and few differences were seen between indoor, outdoor, and night workers. The spectral composition of light was similar for indoor, outdoor, and night workers during days at and off work.

CONCLUSION

The night workers of this study were during night hours on average exposed for a limited time to light intensities expected to suppress melatonin. The indoor workers were exposed to light levels during daylight hours that may reduce general well-being and mood, especially in winter. Outdoor workers were during summer daylight hours exposed to light levels comparable to those used for the treatment of depression.

Melatonin Relations with Energy Metabolism as Possibly Involved in Fatal Mountain Road Traffic Accidents

Previous results evidenced acute exposure to high altitude (HA) weakening the relation between daily melatonin cycle and the respiratory quotient. This review deals with the threat extreme environments pose on body time order, particularly concerning energy metabolism. Working at HA, at poles, or in space challenge our ancestral inborn body timing system. This conflict may also mark many aspects of our current lifestyle, involving shift work, rapid time zone crossing, and even prolonged office work in closed buildings. Misalignments between external and internal rhythms, in the short term, traduce into risk of mental and physical performance shortfalls, mood changes, quarrels, drug and alcohol abuse, failure to accomplish with the mission and, finally, high rates of fatal accidents. Relations of melatonin with energy metabolism being altered under a condition of hypoxia focused our attention on interactions of the indoleamine with redox state, as well as, with autonomic regulations. Individual tolerance/susceptibility to such interactions may hint at adequately dealing with body timing disorders under extreme conditions.

Consequences of Circadian Disruption in Shift Workers on Chrononutrition and their Psychosocial Well-Being

The workers and employees in various institutions are subjected to different shifts and work schedules. The employees work not only at daytime but also during odd hours at night. The biological clock of an individual is often altered during night shifts. This affects the psychosocial well-being and circadian nutritional intake of the worker. Disturbance in circadian rhythm results in the development of metabolic disorders such as hypertension, dyslipidemia, dysglycemia, and abdominal obesity. In the present review, we discuss the nature of shift work, sleep/wake cycle of an individual, chrononutrition, dietary habits, and meal changes with regard to timing and frequency, related to shift work. We also discuss the relationship between nutritional intake and psychosocial well-being among shift workers. The review may be beneficial for prevention of metabolic disorders and maintaining sound psychological condition in shift workers.

The associations between different sleep patterns and osteoporosis based on the Osteoporosis Self-Assessment Tool for Asians

Based on the use of Osteoporosis Self-Assessment Tool for Asians (OSTA) to assess osteoporosis risk, we found that short sleep duration and taking a daytime nap had an increased risk of osteoporosis.

PURPOSE

To explore the associations between different sleep patterns with osteoporosis.

METHODS

3659 postmenopausal women (average age of 60 years) were divided into low, middle, and high osteoporosis risk categories based on the Osteoporosis Self-Assessment Tool for Asians (OSTA). After having collected by a standard questionnaire, total and nocturnal sleep duration was collapsed to form categories of ≤ 6 h, > 6 h and ≤ 7 h, > 7 h and ≤ 8 h, > 8 h and ≤ 9 h, > 9 h, and daytime nap duration of 0 h and > 0 h.

RESULTS

As a categorical variable, the total sleep duration of ≤ 6 h per day (OR = 1.34, 95% CI 1.04-1.72), nocturnal sleep duration of ≤ 6 h per night (OR = 1.65, 95% CI 1.24-2.18), and taking a daytime nap (OR = 1.33, 95% CI 1.09-1.64) had higher osteoporosis risk after adjustment for covariates. As a continuous variable, after the adjustment for covariates, both longer total (OR = 0.86, 95% CI 0.78-0.94) and nocturnal sleep duration (OR = 0.83, 95% CI 0.76-0.91) had lower risk of osteoporosis risk while taking longer daytime nap (OR = 1.10, 95% CI 1.02-1.19) had higher osteoporosis risk.

CONCLUSIONS

Postmenopausal women with both short total and nocturnal sleep duration (6 h or less) and taking a daytime nap had increased osteoporosis risk as assessed by OSTA.

Shift Work, Chronotype, and Melatonin Rhythm in Nurses

BACKGROUND

Previous studies associated night-shift work with melatonin disruption, with mixed evidence regarding the modulating effects of chronotype (i.e., diurnal preference).

METHODS

One hundred and thirty active nurses (84 rotating-shift and 46 day-shift workers) in the Nurses' Health Study II wore a head-mounted light meter and collected spontaneous urine voids over 3 days. 6-Sulfatoxymelatonin (aMT6s), the major urinary metabolite of melatonin, was assessed.

RESULTS

Rotating-shift workers on night shifts had more light exposure and lower urinary melatonin levels during the night, and urinary melatonin rhythms with smaller peaks [11.81 ng/mg-creatinine/h, 95% confidence interval (CI), 9.49-14.71 vs. 14.83 ng/mg-creatinine/h, 95% CI, 11.72-18.75] and later peak onset (5.71 hours, 95% CI, 4.76-6.85 vs. 4.10 hours, 95% CI, 3.37-4.99), compared with day-shift workers. Furthermore, evening chronotypes' melatonin rhythms had later peak onset compared with morning types (4.90 hours, 95% CI, 3.94-6.09 vs. 3.64 hours, 95% CI, 2.99-4.43). However, among day-shift workers, morning chronotypes had melatonin rhythms with greater mean levels, larger peaks, and earlier peak onset compared with evening chronotypes; patterns were similar comparing evening versus morning chronotypes among rotating-shift workers on night shifts. The interaction of rotating-shift work and chronotype was significant across all parameters (P < 0.05).

CONCLUSIONS

As expected, rotating-shift workers on night shifts had greater light exposure and lower urinary melatonin levels during the night compared with day-shift workers. Intriguingly, melatonin rhythms were dependent on both chronotype and rotating-shift work type, and better alignment of rotating-shift work and chronotype appeared to produce less disrupted melatonin rhythms.

IMPACT

The joint effects of shift-work type and chronotype require attention in future studies.

Occupational fatigue and mental health complaints among 8-hour shift workers of petrochemical industries in Iran

BACKGROUND

Shift working is unavoidable in many industries with continual material processing such as petrochemical plants. So, the adverse effects of shift working on workers should be seriously considered.

OBJECTIVE

This cross-sectional study evaluated occupational fatigue and mental health complaints and their relationship in rotating 8-hour shift workers.

METHOD

In this study, 287 shift workers participated. The Multidimensional Fatigue Inventory (MFI-20) and General Health Questionnaire (GHQ-28) were used to evaluate the level of fatigue and mental health, respectively.

RESULT

A relatively high prevalence of mental health complaints (particularly social dysfunction) and fatigue (especially general fatigue) were found among the study population. In general, 43.4% of participants reported a mental health problem. A moderate correlation was found between fatigue and mental health (r = 0.58). The stepwise regression model revealed that fatigue was significantly related only to "anxiety and insomnia" and "severe depression".

CONCLUSION

This study revealed that the 8 h shift workers in studied areas are exposed to a considerable risk of mental health and fatigue. So, improving the ergonomics and health aspects of the workplace is recommended to reduce related risk factors.

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.

Differences in twenty-four-hour profiles of blue-light exposure between day and night shifts in female medical staff

Light is the strongest zeitgeber currently known for the synchronization of the human circadian timing system. Especially shift workers are exposed to altered daily light profiles. Our objective is the characterization of differences in blue-light exposures between day and night shift taking into consideration modifying factors such as chronotype. We describe 24-hour blue-light profiles as measured with ambient light data loggers (LightWatcher) during up to three consecutive days with either day or night shifts in 100 female hospital staff including 511 observations. Linear mixed models were applied to analyze light profiles and to select time-windows for the analysis of associations between shift work, individual factors, and log mean light exposures as well as the duration of darkness per day. Blue-light profiles reflected different daily activities and were mainly influenced by work time. Except for evening (7-9 p.m.), all time windows showed large differences in blue-light exposures between day and night shifts. Night work reduced the duration of darkness per day by almost 4 h (β^ = -3:48 hh:mm, 95% CI (-4:27; -3.09)). Late chronotypes had higher light exposures in the morning and evening compared to women with intermediate chronotype (e.g. morning β^ = 0.50 log(mW/m²/nm), 95% CI (0.08; 0.93)). Women with children had slightly higher light exposures in the afternoon than women without children (β^ = 0.48, 95% CI (-0.10; 1,06)). Time windows for the description of light should be chosen carefully with regard to timing of shifts. Our results are helpful for future studies to capture relevant light exposure differences and potential collinearities with individual factors. Improvement of well-being of shift workers with altered light profiles may therefore require consideration of both - light at the workplace and outside working hours.

Maternal stress and early-onset colorectal cancer

Early-onset colorectal cancer (EOCRC) is defined as colorectal cancer (CRC) diagnosed before the age of 50. Alarmingly, there has been a significant increase in EOCRC diagnoses' worldwide over the past several decades. Emerging data suggest EOCRCs have distinguishing clinical, pathological, biological and molecular features; and thus, are a fundamentally different subtype of CRCs. Unfortunately, there is no simple explanation for the causes of EOCRC. Scientifically rigorous studies are needed to determine what may be driving the challenging epidemiology of EOCRC. We contend here that a reasonable hypothesis is that prenatal risk factors such as maternal stress and associated sleeping disorders influence offspring epigenetic make-up, and shape immune system and gut health contributing to an increased risk for EOCRC.

Physiological reactions to long-term fishing in the Barents Sea

Background

Fishing in distant waters for months may induce physiological stress.

Aims

To assess the physiological stress reactions in fishermen working for 2-3 months continuously in 6-h shifts on trawlers in the Barents Sea.

Methods

The crew of five trawlers fishing in the Barents Sea from January to April 2004 were invited to participate. In the week before and 5-7 days after the trip, the following measures were collected: salivary cortisol four times a day, 24-h urinary cortisol, blood pressure, heart rate, serum cholesterol, serum high-density lipoprotein (HDL-cholesterol), HbA1c (glycosylated haemoglobin) and weight. In addition, 24-h urinary cortisol, blood pressure and heart rate were measured three times. A questionnaire on health, social conditions and work environment was obtained after the trip.

Results

In total, 136 men agreed to participate. Full data were obtained for 96 fishermen (70%). A significant decrease in salivary and urinary cortisol was found during the trip. Adjustment for age, body mass index, smoking, shift work schedule and time of day for sample collection did not change this finding. Systolic and diastolic blood pressure declined significantly and remained significantly lower after the trip compared to before the trip. Serum cholesterol/HDL ratio declined significantly, whereas triglycerides, HbA1c and weight were unchanged.

Conclusions

Working up to 3 months on 6-h shifts, 84 h a week, with moderate physical activity, even in artificial light and cold weather on a ship, did not result in increased physiological stress.

The relationship between night work and breast cancer

Background

Since the International Agency for Research on Cancer classified shift work that involves circadian disruption as “probably carcinogenic to humans,” there has been growing concern on the relationship between night work and breast cancer. In Korea, about 10–15% of workers are engaged in night-shift work, and breast cancer is one of the most common cancers in women. The purpose of this study was to review epidemiologic evidence on the relationship between night work and breast cancer.

Methods

We reviewed 21 original articles and 5 meta analyses on relationship between nightwork and breast cancer, and investigated the compensation criteria of Denmark.

Results

The association between breast cancer and night work has been reported by numerous epidemiologic studies, including cohort studies, case-control studies, and meta-analysis. However, a dose-response relationship has not clearly emerged among workers exposed to less than 20 years of night work.

Conclusion

Although there are some limitations to the epidemiological studies so far, further consideration of breast cancer cases in patients with high exposure to night work is needed to assess breast cancer as a work-related disease.

Measuring Light at Night and Melatonin Levels in Shift Workers: A Review of the Literature

Shift work, especially that involving rotating and night shifts, is associated with an increased risk of diseases, including cancer. Attempts to explain the association between shift work and cancer in particular have focused on the processes of melatonin production and suppression. One hypothesis postulates that exposure to light at night (LAN) suppresses melatonin, whose production is known to slow the development of cancerous cells, while another proposes that circadian disruption associated with shift work, and not just LAN, increases health risks. This review focuses on six studies that employed quantitative measurement of LAN and melatonin levels to assess cancer risks in shift workers. These studies were identified via searching the PubMed database for peer-reviewed, English-language articles examining the links between shift work, LAN, and disease using the terms light at night, circadian disruption, health, risk, cancer, shift work, or rotating shift. While the results indicate a growing consensus on the relationship between disease risks (particularly cancer) and circadian disruption associated with shift work, the establishment of a direct link between LAN and disease has been impeded by contradictory studies and a lack of consistent, quantitative methods for measuring LAN in the research to date. Better protocols for assessing personal LAN exposure are required, particularly those employing calibrated devices that measure and sample exposure to workplace light conditions, to accurately assess LAN's effects on the circadian system and disease. Other methodologies, such as measuring circadian disruption and melatonin levels in the field, may also help to resolve discrepancies in the findings.

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.

The impact of shift work on the psychological and physical health of nurses in a general hospital: a comparison between rotating night shifts and day shifts

BACKGROUND

Shift work is considered necessary to ensure continuity of care in hospitals and residential facilities. In particular, the night shift is one of the most frequent reasons for the disruption of circadian rhythms, causing significant alterations of sleep and biological functions that can affect physical and psychological well-being and negatively impact work performance.

OBJECTIVES

The aim of this study was to highlight if shift work with nights, as compared with day work only, is associated with risk factors predisposing nurses to poorer health conditions and lower job satisfaction.

METHODS

This cross-sectional study was conducted from June 1, 2015 to July 31, 2015 in 17 wards of a general hospital and a residential facility of a northern Italian city. This study involved 213 nurses working in rotating night shifts and 65 in day shifts. The instrument used for data collection was the "Standard Shift Work Index," validated in Italian. Data were statistically analyzed.

RESULTS

The response rate was 86%. The nurses engaged in rotating night shifts were statistically significantly younger, more frequently single, and had Bachelors and Masters degrees in nursing. They reported the lowest mean score in the items of job satisfaction, quality and quantity of sleep, with more frequent chronic fatigue, psychological, and cardiovascular symptoms in comparison with the day shift workers, in a statistically significant way.

CONCLUSION

Our results suggest that nurses with rotating night schedule need special attention due to the higher risk for both job dissatisfaction and undesirable health effects.

Shift work at young age is associated with increased risk of multiple sclerosis in a Danish population

BACKGROUND

Epidemiological studies suggest an important role for environmental factors in developing multiple sclerosis (MS). Furthermore several studies have indicated that the effect of environmental factors may be especially pronounced in adolescents. Recently only one study investigated and found that shift work at young age is associated with an increased risk of developing MS. In this study we focused on the effect of shift work in the vulnerable period between 15-19 years.

OBJECTIVE

The aim of this study was to investigate the association between shift work at young age and the risk of developing MS.

METHODS

We performed a large case-control study including 1723 patients diagnosed with MS and 4067 controls. MS patients were recruited from the Danish Multiple Sclerosis Biobank and controls from The Danish Blood Donor Study. Information on working patterns and lifestyle factors was obtained using a comprehensive lifestyle-environmental factor questionnaire with participants enrolled between 2009 and 2014. Logistic regression models were used to investigate the association between shift work at age 15-19 years and the subsequent risk of MS and were controlled for effects due to established MS risk factors.

RESULTS

We found a statistically significant association when total numbers of night shifts were compared with non-shift workers. For every additional 100 night shifts the odds ratio (OR) for MS was 1.20 (95% confidence interval (CI), 1.08-1.34, p=0.001). Increasing intensity of shift work also increased MS risk. For every additional night per month the OR was 1.04 (95% CI, 1.01-1.06, p=0.002). Duration of shift work in years was not associated with risk of MS.

CONCLUSION

This study supports a statistically significant association between shift work at age 15-19 years and MS risk.

Work schedule and self-reported hypertension - the potential beneficial role of on-shift naps for night workers

Data on the association between shift work and hypertension are controversial. Sleep restriction is hypothesized to be involved in this relationship. Since on-shift nap can partly compensate for sleep deprivation among night workers, this investigation is aimed at (i) comparing the prevalence of hypertension among workers considering both current and former night work, (ii) testing the association between on-shift naps and hypertension among night workers, and (iii) analyzing the influence of sleep complaints in the association between on-shift nap and hypertension. Nap was defined as a sleep episode with duration shorter than the average nighttime sleep. A cross-sectional study was performed at the 18 largest public hospitals in Rio de Janeiro, Brazil, in 2010-2011 (N = 2588 female registered nurses). Nurses were informally allowed to nap for up to three consecutive hours during working nights. Workers completed a multidimensional questionnaire including self-reported information on physician diagnosis of hypertension, napping, and sleep complaints (insomnia, diurnal sleepiness, and non-satisfactory sleep). Epidemiological and statistical treatment of data included binomial logistic regression and interaction tests. Higher chances of hypertension were observed for both current and former night workers compared with workers with no previous experience in night work, i.e. exclusive day workers (OR = 1.68; CI95% 1.22-2.33 and OR = 1.40; CI95% 1.01-1.96, respectively) after adjustment for age, race/ethnicity, physical activity, smoking, alcohol consumption, insomnia, weekly work hours, and BMI. Compared with exclusive day workers, both non-nappers and nappers were at a higher likelihood of reporting hypertension (OR = 1.93 CI95% 1.35-2.79 and OR = 1.41 CI95% 1.08-2.20, respectively). An interaction was observed between napping behavior and insomnia (p = 0.037). In the whole sample of night workers, the lower OR for nappers was confirmed when they were directly compared with non-nappers (OR = 0.76 CI95% 0.59-0.98). Analysis of night workers stratified by insomnia showed a significant reduction in OR for nappers (compared to non-nappers) only among insomniacs (OR = 0.58). Napping during night work may be a protective factor for hypertension, particularly among insomniacs. Factors related to melatonin secretion, blood pressure control, and blood pressure dipping patterns are likely to be involved in the relationship between on-shift napping and blood pressure.

The relationship between quality of sleep and night shift rotation interval

BACKGROUND

Shift work is closely related with workers' health. In particular, sleep is thought to be affected by shift work. In addition, shift work has been reported to be associated with the type or direction of shift rotation, number of consecutive night shifts, and number of off-duty days. We aimed to analyze the association between the night shift rotation interval and the quality of sleep reported by Korean female shift workers.

METHODS

In total, 2,818 female shift workers from the manufacturing industry who received an employee physical examination at a single university hospital from January to August in 2014 were included. Subjects were classified into three groups (A, B, and C) by their night shift rotation interval. The quality of sleep was measured using the Korean version of the Pittsburgh Sleep Quality Index (PSQI). Descriptive analysis, univariate logistic regression, and multivariate logistic regression were performed.

RESULTS

With group A as the reference, the odds ratio (OR) for having a seriously low quality of sleep was 1.456 (95% CI 1.171-1.811) and 2.348 (95% CI 1.852-2.977) for groups B and C, respectively. Thus, group C with the shortest night shift rotation interval was most likely to have a low quality of sleep. After adjustment for age, obesity, smoking status, alcohol consumption, exercise, being allowed to sleep during night shifts, work experience, and shift work experience, groups B and C had ORs of 1.419 (95% CI 1.134-1.777) and 2.238 (95% CI 1.737-2.882), respectively, compared to group A.

CONCLUSION

Our data suggest that a shorter night shift rotation interval does not provide enough recovery time to adjust the circadian rhythm, resulting in a low quality of sleep. Because shift work is influenced by many different factors, future studies should aim to determine the most optimal shift work model and collect accurate, prospective data.

Separate and Joint Associations of Shift Work and Sleep Quality with Lipids

Background

Shift work and/or sleep quality may affect health. We investigated whether shift work and sleep quality, separately and jointly, were associated with abnormal levels of triglycerides, total cholesterol (TC), and low-and high-density lipoprotein cholesterol in 360 police officers (27.5% women).

Methods

Triglycerides, TC, and high-density lipoprotein were analyzed on the Abbott Architect; low-density lipoprotein was calculated. Shift work was assessed using City of Buffalo payroll work history records. Sleep quality (good, ≤ 5; intermediate, 6–8; poor, ≥ 9) was assessed using the Pittsburgh Sleep Quality Index questionnaire. A shift work + sleep quality variable was created: day plus good sleep; day plus poor sleep; afternoon/night plus good; and poor sleep quality. Mean values of lipid biomarkers were compared across categories of the exposures using analysis of variance/analysis of covariance.

Results

Shift work was not significantly associated with lipids. However, as sleep quality worsened, mean levels of triglycerides and TC gradually increased but only among female officers (age- and race-adjusted p = 0.013 and 0.030, respectively). Age significantly modified the association between sleep quality and TC. Among officers ≥ 40 years old, those reporting poor sleep quality had a significantly higher mean level of TC (202.9 ± 3.7 mg/dL) compared with those reporting good sleep quality (190.6 ± 4.0 mg/dL) (gender- and race-adjusted p = 0.010). Female officers who worked the day shift and also reported good sleep quality had the lowest mean level of TC compared with women in the other three categories (p = 0.014).

Conclusion

Sleep quality and its combined influence with shift work may play a role in the alteration of some lipid measures.

Considering the Role of Stress in Populations of High-Risk, Underserved Community Networks Program Centers

BACKGROUND

Cancer disparities are associated with a broad range of sociocultural determinants of health that operate in community contexts. High-risk populations may be more vulnerable to social and environmental factors that lead to chronic stress. Theoretical and empirical research indicates that exposure to contextual and sociocultural stress alters biological systems, thereby influencing cancer risk, progression, and, ultimately, mortality.

OBJECTIVE

We sought to describe contextual pathways through which stress likely increases cancer risk in high-risk, underserved populations.

METHODS

This review presents a description of the link between contextual stressors and disease risk disparities within underserved communities, with a focus on 1) stress as a proximal link between biological processes, such as cytokine responses, inflammation, and cancer and 2) stress as a distal link to cancer through biobehavioral risk factors such as poor diet, physical inactivity, circadian rhythm or sleep disruption, and substance abuse. These concepts are illustrated through application to populations served by three National Cancer Institute-funded Community Networks Program Centers (CNPCs): African Americans in the Deep South (the South Carolina Cancer Disparities Community Network [SCCDCN]), Native Hawaiians ('Imi Hale-Native Hawaiian Cancer Network), and Latinos in the Lower Yakima Valley of Washington State (The Center for Hispanic Health Promotion: Reducing Cancer Disparities).

CONCLUSIONS

Stress experienced by the underserved communities represented in the CNPCs is marked by social, biological, and behavioral pathways that increase cancer risk. A case is presented to increase research on sociocultural determinants of health, stress, and cancer risk among racial/ethnic minorities in underserved communities.

Fatigue and Psychological Distress: A Case Study Among Shift Workers of an Iranian Petrochemical Plant, During 2013, in Bushehr

Background:

Shift work is a well-recognized occupational health hazard in both industrialized and industrially developing countries. Prolonged working time, day/night shift rotation, circadian rhythm and sleep disorders, family and social problems are the most important features of shift working, which have serious complications.

Objectives:

The present study evaluated the fatigue and psychological distress and their relationship among shift workers, in a petrochemical plant (Southern Pars gas field) in Southwest Iran.

Materials and Methods:

In this cross-sectional field study, 400 shift workers from a plant were involved, with participation rate of 72.5% (290 persons). The multidimensional fatigue inventory (MFI-20) and general health questionnaire (GHQ-28) were used to evaluate the level of fatigue and psychological distress, respectively.

Results:

The results showed that the fatigue and psychological distress (particularly social dysfunction, anxiety and insomnia) are frequent among 12-hour shift workers (the total MFI and total GHQ scores were 42.68 ± 17.88 and 34.66 ± 18.56). A relatively strong positive correlation was found between fatigue and psychological distress (r = 0.62). The results of the stepwise regression model indicated that the psychological distress was significantly related only to general fatigue, mental fatigue and reduced motivation, whereas it was not to the physical fatigue and reduced activity.

Conclusions:

The study findings highlight the importance of the mental aspect of fatigue in this working group. These results have possible implications for workers’ health and well-being and for the design of shift work systems, for industrial workers.

The associations of bedtime, nocturnal, and daytime sleep duration with bone mineral density in pre- and post-menopausal women

To explore the association of sleep patterns with bone mineral density (BMD) in pre- and post-menopausal women, we used a questionnaire to evaluate the sleep patterns and performed calcaneal quantitative ultrasound to estimate BMD, in 6,510 women aged 40 years or older, from June to November 2011 in Nanjing City. We found a 1.7-fold risk of osteoporosis in post-menopausalwomen with bedtime of ≥0:00 am (OR = 1.69, 95 % CI 1.39-2.13), compared to those whose bedtime of <0:00 am. post-menopausalwomen with excessive total sleep (>10 h vs. 8-9 h, OR = 1.54, 95 % CI 1.05-2.02) were shown to have a higher risk of osteoporosis, however, this high risk was not detected in those with excessive nocturnal sleep (>10 h vs. 8-9 h, OR = 0.85, 95 % CI 0.62-1.30). By contrast, post-menopausalwomen with inadequate nocturnal sleep (≤7 h vs. 8-9 h, OR = 1.68, 95 % CI 1.32-2.75), excessive daytime sleep (≥180 min vs. 0 min, OR = 1.52, 95 % CI 1.08-2.13), and noontime nap (>60 min vs. 0 min: OR = 1.37, 95 % CI 1.06-1.76) were demonstrated to have higher risk of bone loss. Nevertheless, these associations were not found in premenopausal women. We conclude that delayed bedtime, nocturnal sleep deprivation, excessive daytime sleep, and noontime nap, but not reduced total sleep duration, could promote bone loss in post-menopausalwomen, which might be related to circadian rhythm disturbances. However, they have limited influences to BMD in women who were still in menstruating. Mechanism responsible for the phenomena warrants further investigation.

Increased and mistimed sex hormone production in night shift workers

BACKGROUND

Night shift work has been associated with an increased risk for breast and prostate cancer. The effect of circadian disruption on sex steroid production is a possible underlying mechanism, underinvestigated in humans. We have assessed daily rhythms of sex hormones and melatonin in night and day shift workers of both sexes.

METHODS

We recruited 75 night and 42 day workers, ages 22 to 64 years, in different working settings. Participants collected urine samples from all voids over 24 hours on a working day. Urinary concentrations of 16 sex steroid hormones and metabolites (estrogens, progestagens, and androgens) and 6-sulfatoxymelatonin were measured in all samples. Mean levels and peak time of total and individual metabolite production were compared between night and day workers.

RESULTS

Night workers had higher levels of total progestagens [geometric mean ratio (GMR) 1.65; 95% confidence intervals (CI), 1.17-2.32] and androgens (GMR: 1.44; 95% CI, 1.03-2.00), compared with day workers, after adjusting for potential confounders. The increased sex hormone levels among night shift workers were not related to the observed suppression of 6-sulfatoxymelatonin. Peak time of androgens was significantly later among night workers, compared with day workers (testosterone: 12:14 hours; 10:06-14:48 vs. 08:35 hours; 06:52-10:46).

CONCLUSIONS

We found increased levels of progestagens and androgens as well as delayed peak androgen production in night shift workers compared with day workers.

IMPACT

The increase and mistiming of sex hormone production may explain part of the increased risk for hormone-related cancers observed in night shift workers.

Impacts of shift work on sleep and circadian rhythms

Shift work comprises work schedules that extend beyond the typical "nine-to-five" workday, wherein schedules often comprise early work start, compressed work weeks with 12-hour shifts, and night work. According to recent American and European surveys, between 15 and 30% of adult workers are engaged in some type of shift work, with 19% of the European population reportedly working at least 2 hours between 22:00 and 05:00. The 2005 International Classification of Sleep Disorders estimates that a shift work sleep disorder can be found in 2-5% of workers. This disorder is characterized by excessive sleepiness and/or sleep disruption for at least one month in relation with the atypical work schedule. Individual tolerance to shift work remains a complex problem that is affected by the number of consecutive work hours and shifts, the rest periods, and the predictability of work schedules. Sleepiness usually occurs during night shifts and is maximal at the end of the night. Impaired vigilance and performance occur around times of increased sleepiness and can seriously compromise workers' health and safety. Indeed, workers suffering from a shift work sleep-wake disorder can fall asleep involuntarily at work or while driving back home after a night shift. Working on atypical shifts has important socioeconomic impacts as it leads to an increased risk of accidents, workers' impairment and danger to public safety, especially at night. The aim of the present review is to review the circadian and sleep-wake disturbances associated with shift work as well as their medical impacts.

Melatonin and the skeleton

Melatonin may affect bone metabolism through bone anabolic as well as antiresorptive effects. An age-related decrease in peak melatonin levels at nighttime is well documented, which may increase bone resorption and bone loss in the elderly. In vitro, melatonin reduces oxidative stress on bone cells by acting as an antioxidant. Furthermore, melatonin improves bone formation by promoting differentiation of human mesenchymal stem cell (hMSC) into the osteoblastic cell linage. Bone resorption is reduced by increased synthesis of osteoprogeterin (OPG), a decoy receptor that prevents receptor activator of NK-κB ligand (RANKL) in binding to its receptor. Moreover, melatonin is believed to reduce the synthesis of RANKL preventing further bone resorption. In ovariectomized as well as nonovariectomized rodents, melatonin has shown beneficial effects on bone as assessed by biochemical bone turnover markers, DXA, and μCT scans. Furthermore, in pinealectomized animals, bone mineral density (BMD) is significantly decreased compared to controls, supporting the importance of sufficient melatonin levels. In humans, dysfunction of the melatonin signaling pathway may be involved in idiopathic scoliosis, and the increased fracture risk in nighttime workers may be related to changes in the circadian rhythm of melatonin. In the so-far only randomized study on melatonin treatment, no effects were, however, found on bone turnover markers. In conclusion, melatonin may have beneficial effects on the skeleton, but more studies on humans are warranted in order to find out whether supplementation with melatonin at bedtime may preserve bone mass and improve bone biomechanical competence.

Other than daytime working is associated with lower bone mineral density: the Korea National Health and Nutrition Examination Survey 2009

Occupation affects bone mineral density (BMD); however, only few studies have been published. This study evaluated the effect of working time during a day on BMD. The cross-sectional study involved 18- to 50-year-old people who reported their working time and were measured for BMD using dual-energy X-ray absorptiometry in the Fourth Korea National Health and Nutrition Examination Survey 2009. The time period of work was divided into "daytime" and "other than daytime." The other-than-daytime group included evening time, nighttime, regular shift time, and irregular shift time. Among 3,005 subjects, 2,378 were daytime workers and 627 were other-than-daytime workers. The mean BMD of the total femur and lumbar spine were significantly lower in other-than-daytime workers compared to daytime workers (femur 0.948 vs. 0.966 g/cm², respectively, p = 0.001; lumbar spine 0.976 vs. 0.988 g/cm², respectively, p = 0.023). The other-than-daytime group had lower levels of serum 25-hydroxyvitamin D than the daytime group (16.3 vs. 17.6 ng/mL, p < 0.001). The proportion of osteopenia (T score < -1.0) was higher in the other-than-daytime than the daytime group (34.3 vs. 29.1 %, p = 0.014). After adjustment for age, sex, socioeconomic status, lifestyle factors, daily intake of calcium, and vitamin D level, the relative risks of osteopenia of regular-shift and irregular-shift workers were significantly higher (1.65, 95 % CI 1.05-2.60; 1.78, 95 % CI 1.09-2.89) than those of daytime workers. These data suggest that other-than-daytime working, especially regular and irregular shift working, is associated with decreased BMD and increased risk for osteopenia in Korean adults.

Night shift work and levels of 6-sulfatoxymelatonin and cortisol in men

BACKGROUND

Night shift work is associated with cancer among men, but the biologic mechanism is unclear. We investigated whether male night shift workers showed changes in levels of melatonin and cortisol, potential biomarkers of cancer risk.

METHODS

Urine was collected from 185 night shift and 158 day shift-working male healthcare providers, aged 22 to 55 years, throughout work and sleep periods, and assayed for 6-sulfatoxymelatonin and cortisol. Morning serum was collected within 90 minutes of completing the night and assayed for cortisol.

RESULTS

Night shift workers had significantly lower 6-sulfatoxymelatonin levels during daytime sleep, nighttime work, and nighttime sleep on off-nights (57%, 62%, and 40% lower, respectively), relative to the day shift workers during nighttime sleep (P < 0.0001); urinary cortisol in night shift workers was 16% higher during daytime sleep and 13% lower during nighttime sleep on off-nights (P < 0.05). Morning serum cortisol post-work and post-sleep in night shift workers were 24% and 43% lower, respectively, than post-sleep levels among day shift workers (P < 0.0001). Within-subject comparisons among the night shift workers revealed significantly lower melatonin levels and significantly higher urinary cortisol levels during daytime sleep and nighttime work, relative to nighttime sleep (P < 0.01); morning serum cortisol levels post-work were lower than those post-sleep.

CONCLUSIONS

Night shift workers have substantially lower 6-sulfatoxymelatonin during night work and daytime sleep, and levels remain low when night shift workers sleep at night. Chronic reduction in melatonin among night shift workers may be an important carcinogenic mechanism. Cortisol secretion patterns may be impacted by night shift work, which could affect cancer risk.

IMPACT

Shift work could be an important risk factor for many types of cancer.

The epidemiology of cancer among police officers

BACKGROUND

This review summarizes peer-reviewed studies examining cancer risks among police officers. It provides an overview of existing research limitations and uncertainties and the plausible etiologic risk factors associated with cancer in this understudied occupation.

METHODS

Previous cancer studies among police officers were obtained via a systematic review of the MEDLINE, CABDirect, and Web of Science bibliographic databases.

RESULTS

Quality observational studies of cancer among police officers are sparse and subject to limitations in exposure assessment and other methods. Results from three studies suggested possible increased mortality risks for all cancers, and cancers of the colon, kidney, digestive system, esophagus, male breast, and testis, as well as Hodgkin's disease. Few incidence studies have been performed, and results have been mixed, although some associations with police work have been observed for thyroid, skin, and male breast cancer.

CONCLUSIONS

Police are exposed to a mix of known or suspected agents or activities that increase cancer risk. Epidemiologic evidence to date is sparse and inconsistent. There is a critical need for more research to understand the biological and social processes underlying exposures and the suggested disproportionate risks and to identify effective prevention strategies.

Photic resetting in night-shift work: impact on nurses' sleep

The objective of this study was to quantify daytime sleep in night-shift workers with and without an intervention designed to recover the normal relationship between the endogenous circadian pacemaker and the sleep/wake cycle. Workers of the treatment group received intermittent exposure to full-spectrum bright light during night shifts and wore dark goggles during the morning commute home. All workers maintained stable 8-h daytime sleep/darkness schedules. The authors found that workers of the treatment group had daytime sleep episodes that lasted 7.1 ± .1 h (mean ± SEM) versus 6.6 ± .2 h for workers in the control group (p = .04). The increase in total sleep time co-occurred with a larger proportion of the melatonin secretory episode during daytime sleep in workers of the treatment group. The results of this study showed reestablishment of a phase angle that is comparable to that observed on a day-oriented schedule favors longer daytime sleep episodes in night-shift workers. (Author correspondence: diane.boivin@douglas.mcgill.ca ).

Shift work: health, performance and safety problems, traditional countermeasures, and innovative management strategies to reduce circadian misalignment

There are three mechanisms that may contribute to the health, performance, and safety problems associated with night-shift work: (1) circadian misalignment between the internal circadian clock and activities such as work, sleep, and eating, (2) chronic, partial sleep deprivation, and (3) melatonin suppression by light at night. The typical countermeasures, such as caffeine, naps, and melatonin (for its sleep-promoting effect), along with education about sleep and circadian rhythms, are the components of most fatigue risk-management plans. We contend that these, while better than nothing, are not enough because they do not address the underlying cause of the problems, which is circadian misalignment. We explain how to reset (phase-shift) the circadian clock to partially align with the night-work, day-sleep schedule, and thus reduce circadian misalignment while preserving sleep and functioning on days off. This involves controlling light and dark using outdoor light exposure, sunglasses, sleep in the dark, and a little bright light during night work. We present a diagram of a sleep-and-light schedule to reduce circadian misalignment in permanent night work, or a rotation between evenings and nights, and give practical advice on how to implement this type of plan.

Circadian disruption, sleep loss, and prostate cancer risk: a systematic review of epidemiologic studies

Disruption of the circadian system has been hypothesized to increase cancer risk, either because of direct disruption of the molecular machinery generating circadian rhythms or because of disruption of parameters controlled by the clock such as melatonin levels or sleep duration. This hypothesis has been studied in hormone-dependent cancers among women, but data are sparse about potential effects of circadian disruption on the risk of prostate cancer. This review systematically examines available data evaluating the effects of light at night, sleep patterns, and night shift work on prostate cancer risk.