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Objectives This study aimed to evaluate occupational exposures and menstrual cycle characteristics among nurses. Methods Using cross-sectional data collected in 2010–2012 from 6309 nurses aged 21–45 years, we investigated nurses' menstrual function in the Nurses' Health Study 3. We used multivariable regression modeling to analyze the associations between occupational exposures and prevalence of irregular cycles and long and short cycle lengths. Results The cohort reported cycle length as <21 (1.5%), 21–25 (15.6%), 26–31 (69.7%), and 32–50 (13.2%) days. In addition, 19% of participants reported irregular cycles. Working ≥41 hours/week was associated with a 16% [95% confidence interval (95% CI): 4–29%] higher prevalence of irregular cycles and a higher prevalence of very short (<21-day) cycles [prevalence odds ratio (OR) 1.93, 95% CI 1.24–3.01] in adjusted models. Irregular menstrual cycles were more prevalent among women working nights only (32% higher; 95% CI 15–51%) or rotating nights (27% higher, 95% CI 10–47%), and was associated with the number of night shifts per month (P for trend <0.0001). Rotating night schedule was associated with long (32–50 day) cycles (OR 1.28, 95% CI 1.03–1.61). Heavy lifting was associated with a higher prevalence of irregular cycles (34% higher), and the prevalence of cycles <21 days and 21–25 day cycles increased with increasing heavy lifting at work (P for trend <0.02 for each endpoint). Conclusion Night work, long hours, and physically demanding work might relate to menstrual disturbances.

Background Night–shift work may cause severe disturbances in the worker’s circadian rhythm, which has been associated with the onset of health problems and diseases. As a substantial part of the workforce is exposed to night–shift work, harmful aspects of night–shift work should not be overlooked. The aim of the Klokwerk + study is to study the effects of night–shift work on body weight and infection susceptibility and the mechanisms underlying these health effects. First, we will study the relation between night–shift work exposure and body weight and between night–shift work exposure and infection susceptibility. Second, we will examine the mechanisms linking night–shift work exposure to body weight and infection susceptibility, with a specific focus on sleep, physical activity, diet, light exposure, vitamin D level, and immunological factors. Lastly, we will focus on the identification of biomarkers for chronic circadian disturbance associated with night–shift work. Methods/design The design of this study is a prospective observational cohort study consisting of 1,960 health care workers aged 18–65 years. The study population will consist of a group of night–shift workers and an equally sized group of non–night–shift workers. During the study, there will be two measurement periods. As one of the main outcomes of this study is infection susceptibility, the measurement periods will take place at approximately the first (September/October) (T0) and the last month (April/May) (T1, after 6 months) of the flu season. The measurements will consist of questionnaires, anthropometric measurements, a smartphone application to determine infection susceptibility, food diaries, actigraphy, light sensors, and blood sample analyses. Discussion The Klokwerk + study will contribute to the current need for high–quality data on the health effects of night–shift work and its underlying behavioral and physiological mechanisms. The findings can be the starting point for the development of interventions that prevent negative health effects caused by night–shift work. In addition, the identification of biomarkers indicative of loss of homeostasis due to circadian disturbance may be an important asset in monitoring the effects of such interventions.

Objectives This discussion paper aims to provide scientifically based recommendations on night shift schedules, including consecutive shifts, shift intervals and duration of shifts, which may reduce health and safety risks. Short-term physiological effects in terms of circadian disruption, inadequate sleep duration and quality, and fatigue were considered as possible links between night shift work and selected health and safety risks, namely, cancer, cardio-metabolic disease, injuries, and pregnancy-related outcomes. Method In early 2020, 15 experienced shift work researchers participated in a workshop where they identified relevant scientific literature within their main research area. Results Knowledge gaps and possible recommendations were discussed based on the current evidence. The consensus was that schedules which reduce circadian disruption may reduce cancer risk, particularly for breast cancer, and schedules that optimize sleep and reduce fatigue may reduce the occurrence of injuries. This is generally achieved with fewer consecutive night shifts, sufficient shift intervals, and shorter night shift duration. Conclusions Based on the limited, existing literature, we recommend that in order to reduce the risk of injuries and possibly breast cancer, night shift schedules have: (i) ≤3 consecutive night shifts; (ii) shift intervals of ≥11 hours; and (iii) ≤9 hours shift duration. In special cases - eg, oil rigs and other isolated workplaces with better possibilities to adapt to daytime sleep - additional or other recommendations may apply. Finally, to reduce risk of miscarriage, pregnant women should not work more than one night shift in a week.

Night shift work has been suspected to increase breast cancer risk but epidemiological studies have been inconsistent due to heterogeneous assessment of exposure to night work. To overcome this limitation, we pooled data of five population-based case-control studies from Australia, Canada, France, Germany, and Spain into a single harmonized dataset using a common definition of night work including 6093 breast cancer cases and 6933 population controls. The odds ratio for breast cancer in women who ever worked at night for at least 3 h between midnight and 5 a.m. as compared to never night workers was 1.12 (95% CI 1.00-1.25). Among pre-menopausal women, this odds ratio was 1.26 [1.06-1.51], increasing to 1.36 [1.07-1.74] for night shifts ≥ 10 h, 1.80 [1.20-2.71] for work ≥ 3 nights/week, and 2.55 [1.03-6.30] for both duration of night work ≥ 10 years and exposure intensity ≥ 3 nights/week. Breast cancer risk in pre-menopausal women was higher in current or recent night workers (OR = 1.41 [1.06-1.88]) than in those who had stopped night work more than 2 years ago. Breast cancer in post-menopausal women was not associated with night work whatever the exposure metric. The increase in risk was restricted to ER+ tumors, particularly those who were both ER+ and HER2+ . These results support the hypothesis that night shift work increases the risk of breast cancer in pre-menopausal women, particularly those with high intensity and long duration of exposure. Risk difference between pre- and post-menopausal women deserves further scrutiny.

Zdravstvena zaštita u Republici Hrvatskoj organizirana je na primarnoj, sekundarnoj, tercijarnoj te razini zdravstvenih zavoda. Većina medicinskih sestara i tehničara radi na sekundarnoj i tercijarnoj razini koja uključuje kontinuiranu 24-satnu skrb te je iz tog razloga i najveći broj medicinskih sestara i tehničara izloženo utjecaju noćnog rada. Noćni rad utječe na zdravlje na način da dovodi do deprivacije sna, umora, rizika za psihičke i fizičke smetnje te bolesti, ali i poremećaje u socijalnom i obiteljskom životu. Pretražene su 3 baze podataka: Pubmed, Google scholar i Proquest; kriterij za odabir bio je sustavni pregled literature i meta analiza, a u obzir su dolazili samo članci na engleskom jeziku. Pregled literature rađen je prema PRISMA smjernicama, kvaliteta članaka ocijenjena je AMSTAR-R instrumentom za ocjenjivanje, pouzdanost između ocjenjivača napravljena je Cohenovim kappa koeficijentom, a kako bi se utvrdilo preklapanje korištene literature korištena je metoda ispravljenog pokrivenog područja (eng. Corrected Covered Area (CCA)). Pregledom sustavnih pregleda i meta analiza, rezultati prikazani u ovom radu dobiveni su iz 8 istraživanja od kojih su 3 sistematski pregled, a 5 meta analize, objavljivani između 2013. i 2021. godine iz različitih dijelova svijeta (Europa, Azija, Amerika, Australija, Afrika). Istraživanja su pokazala da noćni rad utječe na san medicinskih sestara u smislu smanjenja njegove kvalitete te na samo zdravlje u smislu povećanja rizika od povećane težine, razvoja metaboličkog sindroma, dijabetesa tipa 2, kardiovaskularnih bolesti, karcinoma dojke, bolova u leđima te povećanja unosa alkohola. Osim utjecaja na san i zdravlje medicinskih sestara, noćni rad može dovesti i do drugih rizika kako za medicinske sestre poput rizika od ubodnih incidenata, ozljeda i bolova, psihičkih i emocionalnih smetnji, željom za odlaskom te automobilskih nesreća, tako i za krajnje korisnike zdravstvene zaštite, a to su pacijenti, a odnose se na rizik od pogrešne administracije lijekova, dekubitusa, hipoglikemije, urinarne infekcije te bolničke infekcije. Potrebna su dodatna istraživanja povezana s problematikom noćnog rada kako za same rizike koje on donosi tako i za utjecaj potencijalnih rješenja na iste. Osim toga, potrebna je trajna edukacija medicinskih sestara o ovom problemu kako bi se na vrijeme prepoznale posljedice, na njih pravovremeno reagiralo te na taj način smanjile dugoročne posljedice na zdravlje. Nužno je i kontinuirano praćenje zdravstvenog stanja te poboljšanje radnih uvjeta u skladu s procjenom rizika pojedinog radilišta. Health care in the Republic of Croatia is organized at the primary, secondary, tertiary and health care institutions. Most nurses and technicians work at the secondary and tertiary levels, which includes continuous 24-hour care, and for this reason most nurses and technicians are exposed to night work. Night work affects health in a way that leads to sleep deprivation, fatigue, risk of mental and physical disorders and illnesses, but also disturbances in social and family life. 3 databases were searched: Pubmed, Google scholar and Proquest, the selection criteria were a systematic review of the literature and meta-analyzes, and only articles in English were considered. The literature review was performed according to PRISMA guidelines, the quality of the articles was evaluated by the AMSTAR-R evaluation instrument, the reliability between evaluators was made by the Cohen kappa coefficient, and the Corrected Covered Area (CCA) method was used to determine the overlap of the used literature. )). A review of systematic reviews and meta-analyzes, the results presented in this paper were obtained from 8 studies, 3 of which are systematic reviews, and 5 meta-analyzes, were published between 2013 and 2021 from different parts of the world (Europe, Asia, America) , Australia, Africa). Research has shown that night work affects nurses' sleep in terms of reducing its quality, and health itself in terms of increasing the risk of weight gain, developing metabolic syndrome, type 2 diabetes, cardiovascular disease, breast cancer, back pain and increasing alcohol intake. In addition to the impact on nurses' sleep and health, night work can lead to other risks for nurses, such as the risk of needlestick incidents, injuries and pain, mental and emotional disturbances, the desire to leave and car accidents, and for end users of health care, which are patients, risk of mismanagement of drugs, pressure ulcers, hypoglycemia, urinary tract infections and nosocomial infections. Additional research is needed related to the issue of night work, both with the risks it brings and the impact of potential solutions on them. Continuous education of nurses on this problem is needed in order to timely recognize the consequences of responding to them in a timely manner and thus reduce long-term health consequences. It is also necessary to continuously monitor the health condition and improve working conditions in accordance with the risk assessment of each site.

Objective The aim of this review was to synthesize the evidence on the potential relationship between nightshift work and breast cancer. Methods We searched multiple databases for studies comparing women in shift work to those with no-shift work reporting incidence of breast cancer. We calculated incremental risk ratios (RR) per five years of nightshift work and per 300 night shift increases in exposure and combined these in a random effects dose—response meta-analysis. We assessed study quality in ten domains of bias. Results We identified 16 studies: 12 case—control and 4 cohort studies. There was a 9% risk increase per five years of night-shift work exposure in case—control studies [RR 1.09, 95% confidence interval (95% CI) 1.02—1.20; I 2 =37%, 9 studies], but not in cohort studies (RR 1.01, 95% CI 0.97—1.05; I 2 =53%, 3 studies). Heterogeneity was significant overall (I 2 =55%, 12 studies). Results for 300 night shifts were similar (RR 1.04, 95% CI 1.00—1.10; I 2 =58%, 8 studies). Sensitivity analysis using exposure transformations such as cubic splines, a fixed-effect model, or including only better quality studies did not change the results. None of the 16 studies had a low risk of bias, and 6 studies had a moderate risk. Conclusions Based on the low quality of exposure data and the difference in effect by study design, our findings indicate insufficient evidence for a link between night-shift work and breast cancer. Objective prospective exposure measurement is needed in future studies.

Misalignment of the endogenous circadian timing system leads to disruption of physiological rhythms and may contribute to the development of the deleterious health effects associated with night shift work. However, the molecular underpinnings remain to be elucidated. Here, we investigated the effect of a 4-day simulated night shift work protocol on the circadian regulation of the human transcriptome. Repeated blood samples were collected over two 24-hour measurement periods from eight healthy subjects under highly controlled laboratory conditions before and 4 days after a 10-hour delay of their habitual sleep period. RNA was extracted from peripheral blood mononuclear cells to obtain transcriptomic data. Cosinor analysis revealed a marked reduction of significantly rhythmic transcripts in the night shift condition compared with baseline at group and individual levels. Subsequent analysis using a mixed-effects model selection approach indicated that this decrease is mainly due to dampened rhythms rather than to a complete loss of rhythmicity: 73% of transcripts rhythmically expressed at baseline remained rhythmic during the night shift condition with a similar phase relative to habitual bedtimes, but with lower amplitudes. Functional analysis revealed that key biological processes are affected by the night shift protocol, most notably the natural killer cell-mediated immune response and Jun/AP1 and STAT pathways. These results show that 4 days of simulated night shifts leads to a loss in temporal coordination between the human circadian transcriptome and the external environment and impacts biological processes related to the adverse health effects associated to night shift work.

Abstract Study Objectives A critical barrier to successful treatment of circadian misalignment in shift workers is determining circadian phase in a clinical or field setting. Light and movement data collected passively from wrist actigraphy can generate predictions of circadian phase via mathematical models; however, these models have largely been tested in non-shift working adults. This study tested the feasibility and accuracy of actigraphy in predicting dim light melatonin onset (DLMO) in fixed night shift workers. Methods A sample of 45 night shift workers wore wrist actigraphs before completing DLMO in the laboratory (17.0 days ± 10.3 SD). DLMO was assessed via 24 hourly saliva samples in dim light (<10 lux). Data from actigraphy were provided as input to a mathematical model to generate predictions of circadian phase. Agreement was assessed and compared to average sleep timing on non-workdays as a proxy of DLMO. Model code and an open-source prototype assessment tool are available (www.predictDLMO.com). Results Model predictions of DLMO showed good concordance with in-lab DLMO, with Lin’s concordance coefficient of 0.70, which was twice as high as agreement using average sleep timing as a proxy of DLMO. The absolute mean error of the predictions was 2.88 h, with 76% and 91% of the predictions falling with 2 and 4 h, respectively. Conclusion This study is the first to demonstrate the use of wrist actigraphy-based estimates of circadian phase as a clinically useful and valid alternative to in-lab measurement of DLMO in fixed night shift workers. Future research should explore how additional predictors may impact accuracy.

Objectives The organization of night shift work affects sleep duration and quality. The aim of this study was to investigate the effects of the number of consecutive night shifts on sleep duration and quality among police officers with night shift work as part of their normal schedule. Methods This quasi-experimental, within-subject crossover study included 73 police officers. All participants performed three work schedules: two, four and seven consecutive night shifts followed by the same number of recovery days, ie, day work or days off (2+2, 4+4, and 7+7). Sleep assessed through sleep diaries and actigraphy after all night shifts and recovery days (totaling 26 days) was compared by use of repeated measures analysis. Results Participants experienced shorter sleep duration (with and without naps), more premature awakening, less difficulty falling asleep, and more non-refreshing sleep after night shifts compared with recovery days. Sleep duration and quality did not change with increasing number of consecutive night shifts. Sleep was shorter and of poorer quality after the last night shift in the 2+2 and 4+4 work schedule compared with the second and fourth night shift, respectively, in the 7+7 schedule. Conclusion Sleep duration was reduced after night shift work and did not increase with more consecutive night shifts, which leads to accumulated sleep debt. Sleep duration was shortest and sleep quality was poorest after the last night shift in a series of night shifts.

OBJECTIVES: A growing body of research on infection susceptibility among night-shift workers has emerged, particularly since the COVID-19 pandemic. However, a comprehensive overview is still lacking. Therefore, this review aimed to synthesize the evidence on the association between night-shift work and susceptibility to infectious diseases. METHODS: Embase and PsycINFO were systematically searched for studies published up to September 2024. Studies were included if they comprised a working population, night-shift workers were compared to non-shift workers, and the outcome was an infectious disease. Results were descriptively synthesized for common respiratory infections (flu and common cold), SARS-CoV-2 infection, and other infections. Pooled effect estimates were calculated using random-effects meta-analysis. RESULTS: In total, 16 articles describing 14 studies among 191 320 workers were included. Based on 4 studies, night-shift work was not associated with a significantly increased risk of common respiratory infections [odds ratio (OR) 1.11, 95% confidence interval (CI) 0.97–1.27, I 2 =65.8%[. However, night-shift workers had a higher risk of SARS-CoV-2 infection than non-shift workers (OR 1.31, 95% CI 1.09–1.58, I 2 =92.2%, N=10 studies). This association was stronger in higher-quality studies and studies conducted in the first year of the COVID-19 pandemic. For other infections, insufficient studies were available to conduct a meta-analysis. The certainty of evidence was graded very low due to a limited number of (prospective cohort) studies and high inconsistency in the available studies. CONCLUSIONS: This systematic review and meta-analysis showed that night-shift work was associated with an increased risk of SARS-CoV-2 infection, but not of common respiratory infections. To address the lack of high-certainty evidence, more studies are needed that apply a prospective design with appropriate adjustment for confounding factors and more extensive information on night-shift work exposure.