Intraindividual association between shift work and risk of drinking problems: data from the Finnish Public Sector Cohort

ObjectivesStudies concerning the association between shift work and drinking problems showed inconsistent results. We used data from a large occupational cohort to examine the association between shift work and different types of drinking behaviour.MethodsA total of 93 121 non-abstinent workers from the Finnish Public Sector Study were enrolled in the study. Six waves of survey data were collected between 2000 and 2017. Work schedules were categorised as regular day, non-night shift and night shift work, and shift intensities were calculated from registered working hour data. Two indicators of adverse drinking behaviour were measured: at-risk drinking (>7 and >14 drinks per week in women and men, respectively) and high-intensity drinking (measured as pass-out experience). Intraindividual analysis was conducted using fixed-effects regression to examine the association between shift work and drinking behaviours.ResultsCompared with regular day work, night shift work was associated with an increased risk of high-intensity drinking (OR 1.28, 95% CI 1.07 to 1.52) but a lower risk of at-risk drinking (OR 0.85, 95% CI 0.74 to 0.99). Shift workers who worked long shifts had a lower risk of at-risk drinking compared with those who rarely worked long shifts (OR 0.58, 95% CI 0.37 to 0.93).ConclusionsAssociations between shift work and alcohol use vary according to drinking patterns. Workers engaged in high-intensity drinking more often during night shift schedules compared with day work, but did not drink averagely higher volume.

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Is shift-work associated with increased risk of rectal cancer? A meta-analysis.

Journal of Clinical Oncology ◽

10.1200/jco.2021.39.15_suppl.e15600 ◽

2021 ◽

Vol 39 (15_suppl) ◽

pp. e15600-e15600

Author(s):

Chenyu Sun ◽

Ce Cheng ◽

Kelly Kozma ◽

Gopika Chandra ◽

Na Hyun Kim ◽

...

Keyword(s):

Rectal Cancer ◽

Cancer Risk ◽

Shift Work ◽

Meta Analysis ◽

Night Shift ◽

Fixed Effect Model ◽

Night Shift Work ◽

Increased Risk ◽

Rotating Shift Work ◽

Trim And Fill

e15600 Background: Globally, more than 1.8 million people were diagnosed of colorectal cancer (CRC) in 2018, with over 30% of CRC in the rectum. Shift-work, involving circadian disruption, sleep deprivation and lifestyle changes, was designated as a probable cause of cancer by The International Agency for Research on Cancer. Previous studies investigating the impact of permanent night-shift work and rotating shift-work on rectal cancer risk showed controversial results. Thus, this meta-analysis was conducted. Methods: A comprehensive literature search on PubMed was conducted to identify all relevant studies published prior to January 2021 according to the established inclusion criteria. The quality assessment was performed by the Newcastle-Ottawa Scale (NOS). The pooled odds ratio (OR) and 95% confidence intervals (CI) were calculated to estimate the association between the shift-work and rectal cancer risk. Based on heterogeneity significance, random-effect or fixed-effect model was used. Subgroup analyses were conducted to explore the night-shift and rotating-shift, respectively. Sensitivity analysis and publication bias detection were performed, and trim and fill analysis was also conducted. All statistical analyses were performed using RevMan software (version 5.3; Cochrane library) and STATA 15.0 statistical software (Stata Corp., College Station, TX), and all P values were two-tailed, the test level was 0.05. Results: Thirty-seven articles were obtained from database searching. Three articles involving 1,063 rectal cancer cases were included. All studies were considered moderate to high quality. All included studies investigated on the association between shift-work and rectal cancer risk. A statistically significant association between shift-work and increased rectal cancer risk was found (OR 1.53, 95%CI: 1.31, 1.79, P< 0.00001, I 2 = 35%). In subgroup analyses, night-shift work was associated with a non-statistically significant increased risk of rectal cancer (OR 1.25, 95%CI: 0.47, 3.32, P = 0.66, I 2 = 93%). In contrast, Rotating-shift was associated with a statistically significant increased rectal cancer risk (OR 1.35, 95%CI: 1.10, 1.65, P = 0.004, I 2 = 6%). Sensitivity analysis confirmed the stability of the result. Funnel plot, Egger's test (t = 1.69, P = 0.341), and Begg's test (z = 1.04, P = 0.296) found no publication bias of analysis. Trim and fill analysis on fixed-effect model showed the pooled OR kept stable after adding two “missing” studies (OR 1.403, 95%CI: 1.224, 1.609, P <0.05). Conclusions: The current meta-analysis demonstrates that shift-work is associated with increased rectal cancer risk. However, no association between night-shift work and rectal cancer risk was found. In contrast, association between rotating-shift work and increased rectal cancer risk was found. More original studies on this topic are needed to further explore shift-work impacts on rectal cancer risk.

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Night Shift Work Accelerates Menopausal Age in Health Workers

Biomolecular and Health Science Journal ◽

10.20473/bhsj.v4i1.25361 ◽

2021 ◽

Vol 4 (1) ◽

pp. 30

Author(s):

Sri Ratna Dwiningsih ◽

Samsulhadi Samsulhadi ◽

Arif Tunjungseto ◽

Monika Lijuwardi ◽

Arsana Wiyasa

Keyword(s):

Nutritional Status ◽

Shift Work ◽

Health Workers ◽

Risk Group ◽

Lymphoblastic Leukemia ◽

Night Shift ◽

Induction Phase ◽

Night Shift Work ◽

Increased Risk ◽

History Of

Introduction: Earlier menopause has been associated with increased risk of cardiovascular disease, osteoporosis, shorter life expectancy and even cognitive decline. There are many factors that cause differences in the age of menopause in women, one of these environmental factors is a history of night shift work as a consequence of a job. It is not yet known whether female medical workers, with a history of night shifts, get earlier menopause.Methods: This case control study was conducted among 57 female night workers of the Dr. Soetomo General Academic Hospital. Data collection was conducted from December 2019 - March 2020. The study sample was postmenopausal health workers (nurse and midwife) and administrators. The instrument used in this study was a list of interview questions. The data was processed using SPSS software release 23.Results: The results show that from 45 children diagnosed with ALL, 53% are of the age ≤ 5 years old, with 58% males and 42% females. 13% of the patients are in the high risk group and 87% are in the standard risk group. Nutritional statuses of patients are 2% of them obese experienced remission after induction phase therapy, 56% normal with 80% of them experienced remission. 40% underweight with 89% of them experienced remission and 11% not experienced remission, 2% malnutrition and experienced remission. There is no correlation between the nutritional status of children with acute lymphoblastic leukemia with the outcome of induction phase (p = 0.798).Conclusion: In conclusion, there is no correlation between nutritional status and remission outcome of patients with ALL in the induction phase of therapy. However, high percentage of underweight patients shows nutrition needs special attention to improve therapy outcomes.

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Is shift-work associated with increased risk of esophageal cancer for males? A meta-analysis.

Journal of Clinical Oncology ◽

10.1200/jco.2021.39.3_suppl.190 ◽

2021 ◽

Vol 39 (3_suppl) ◽

pp. 190-190

Author(s):

Chenyu Sun ◽

Ce Cheng

Keyword(s):

Sensitivity Analysis ◽

Esophageal Cancer ◽

Cancer Risk ◽

Publication Bias ◽

Shift Work ◽

Meta Analysis ◽

Night Shift ◽

Night Shift Work ◽

Increased Risk ◽

Subgroup Analyses

190 Background: Globally, more than 570,000 people are diagnosed of esophageal cancer each year. Shift-work involving circadian disruption was designated as a probable cause of cancer by The International Agency for Research on Cancer. Previous studies investigating the relationship between shift-work and esophageal cancer among showed controversial results. Thus, this meta-analysis was conducted. Methods: A comprehensive literature search on PubMed was conducted to identify all relevant studies published prior to September 2020 according to the established inclusion criteria. The quality assessment was performed by the Newcastle-Ottawa Scale (NOS). The pooled odds risk (OR) and 95% confidence intervals (CI) were calculated to estimate the association between the shift-work and esophageal cancer risk. Random-effect or fixed-effect model was used to calculate the pooled OR, based on heterogeneity significance. Subgroup analyses were conducted based on night-shift versus rotating-shift. Sensitivity analysis and publication bias detection were also performed. All statistical analyses were performed using RevMan software (version 5.3; Cochrane library) and STATA 12.0 statistical software (Stata Corp., College Station, TX), and all P values were two-tailed, the test level was 0.05. Results: 21 articles were obtained from database searching, and 9 articles were obtained from other sources. 3 articles involving 52,098 participants were included. All studies were considered moderate to high quality. All included studies investigated only males on the association between shift-work and esophageal cancer risk. A statistically significant association between shift-work and increased esophageal cancer risk among males was found (OR 2.09, 95%CI: 1.48, 2.94, P< 0.0001, I 2= 29%). In subgroup analyses, night-shift work was associated with a non-statistically significant increased risk of esophageal cancer (OR 1.56, 95%CI: 0.96, 2.53, P= 0.07, I 2= 0%). In contrast, Rotating-shift was associated with increased esophageal cancer risk (OR 2.80, 95%CI: 1.72, 4.57, P < 0.0001, I 2= 0%). Sensitivity analysis confirmed the stability of the result. Funnel plot, Egger's test, and Begg's test found no publication bias of analysis (P = 0.572). Conclusions: The current meta-analysis demonstrates that shift-work is associated with increased esophageal cancer risk for males. However, no association between night-shift work and esophageal cancer risk was found. In contrast, association between rotating-shift work and increased esophageal cancer risk was found. Original studies on females regarding shift-work and esophageal cancer risk are lacking. More original studies on this topic for both male and female are needed to further explore shift-work impacts on esophageal cancer risk.

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Rotating night shift work and risk of multiple sclerosis in the Nurses’ Health Studies

Occupational and Environmental Medicine ◽

10.1136/oemed-2019-106016 ◽

2019 ◽

Vol 76 (10) ◽

pp. 733-738 ◽

Cited By ~ 1

Author(s):

Kyriaki Papantoniou ◽

Jennifer Massa ◽

Elizabeth Devore ◽

Kassandra L Munger ◽

Tanuja Chitnis ◽

...

Keyword(s):

Multiple Sclerosis ◽

Shift Work ◽

Proportional Hazards ◽

Night Shift ◽

Cox Proportional Hazards ◽

Health Study ◽

Work History ◽

Night Shift Work ◽

Increased Risk ◽

History Of

ObjectivesNight shift work has been suggested as a possible risk factor for multiple sclerosis (MS). The objective of the present analysis was to prospectively evaluate the association of rotating night shift work history and MS risk in two female cohorts, the Nurses’ Health Study (NHS) and NHSII.MethodsA total of 83 992 (NHS) and 114 427 (NHSII) women were included in this analysis. We documented 579 (109 in NHS and 470 in NHSII) incident physician-confirmed MS cases (moderate and definite diagnosis), including 407 definite MS cases. The history (cumulative years) of rotating night shifts (≥3 nights/month) was assessed at baseline and updated throughout follow-up. Cox proportional hazards models were used to estimate HRs and 95% CIs for the association between rotating night shift work and MS risk adjusting for potential confounders.ResultsWe observed no association between history of rotating night shift work and MS risk in NHS (1–9 years: HR 1.03, 95% CI 0.69 to 1.54; 10+ years: 1.15, 0.62 to 2.15) and NHSII (1–9 years: HR 0.90, 95% CI 0.74 to 1.09; 10+ years: 1.03, 0.72 to 1.49). In NHSII, rotating night shift work history of 20+ years was significantly associated with MS risk, when restricting to definite MS cases (1–9 years: HR 0.88, 95% CI 0.70 to 1.11; 10–19 years: 0.98, 0.62 to 1.55; 20+ years: 2.62, 1.06 to 6.46).ConclusionsOverall, we found no association between rotating night shift work history and MS risk in these two large cohorts of nurses. In NHSII, shift work history of 20 or more years was associated with an increased risk of definite MS diagnosis.

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A Rodent Model of Night-Shift Work Induces Short-Term and Enduring Sleep and Electroencephalographic Disturbances

Journal of Biological Rhythms ◽

10.1177/0748730416675460 ◽

2016 ◽

Vol 32 (1) ◽

pp. 48-63 ◽

Cited By ~ 9

Author(s):

Janne Grønli ◽

Peter Meerlo ◽

Torhild T. Pedersen ◽

Ståle Pallesen ◽

Silje Skrede ◽

...

Keyword(s):

Shift Work ◽

Slow Wave ◽

Night Shift ◽

Active Phase ◽

Nrem Sleep ◽

Night Work ◽

Brain State ◽

Work Schedule ◽

Night Shift Work ◽

Increased Risk

Millions of people worldwide are working at times that overlap with the normal time for sleep. Sleep problems related to the work schedule may mediate the well-established relationship between shift work and increased risk for disease, occupational errors and accidents. Yet, our understanding of causality and the underlying mechanisms that explain this relationship is limited. We aimed to assess the consequences of night-shift work for sleep and to examine whether night-shift work-induced sleep disturbances may yield electrophysiological markers of impaired maintenance of the waking brain state. An experimental model developed in rats simulated a 4-day protocol of night-work in humans. Two groups of rats underwent 8-h sessions of enforced ambulation, either at the circadian time when the animal was physiologically primed for wakefulness (active-workers, mimicking day-shift) or for sleep (rest-workers, mimicking night-shift). The 4-day rest-work schedule induced a pronounced redistribution of sleep to the endogenous active phase. Rest-work also led to higher electroencephalogram (EEG) slow-wave (1-4 Hz) energy in quiet wakefulness during work-sessions, suggesting a degraded waking state. After the daily work-sessions, being in their endogenous active phase, rest-workers slept less and had higher gamma (80-90 Hz) activity during wake than active-workers. Finally, rest-work induced an enduring shift in the main sleep period and attenuated the accumulation of slow-wave energy during NREM sleep. A comparison of recovery data from 12:12 LD and constant dark conditions suggests that reduced time in NREM sleep throughout the recorded 7-day recovery phase induced by rest-work may be modulated by circadian factors. Our data in rats show that enforced night-work-like activity during the normal resting phase has pronounced acute and persistent effects on sleep and waking behavior. The study also underscores the potential importance of animal models for future studies on the health consequences of night-shift work and the mechanisms underlying increased risk for diseases.

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Hubungan Kerja Shift Malam dan Kejadian Kanker Payudara Pada Pekerja Wanita: Tinjauan Kasus Berbasis Bukti

Pro Health Jurnal Ilmiah Kesehatan ◽

10.35473/proheallth.v2i1.386 ◽

2020 ◽

Vol 2 (1) ◽

Author(s):

Ayu Munawaroh

Keyword(s):

Breast Cancer ◽

Shift Work ◽

Service Sector ◽

Meta Analysis ◽

Night Shift ◽

International Agency ◽

Night Shift Work ◽

Female Workers ◽

Increased Risk ◽

Negative Impacts

Within the last decade, shift work has been an important issue, because it can give negative impacts to the worker’s body. International Agency for Research on Cancer (IARC) on 2007 had classified the shift work which disturb circadian rhythm as probably carcinogenic. One of the cancer which often been researched is breast cancer. Moreover, Around 572% of female workers are in professional and service sector that closely related to night shift work. This evidence based case report aims to know the relation between night shift work and breast cancer in female workers. Based on electronic database literature searching on September 26th 2018 using PubMed, EBSCo (MEDLINE with fulltext), and ProQuest, there are seven meta-analysis which useful to be critically appraised. The result of critical appraisal was increased risk of breast cancer in night shift female workers. Therefore, there was a sufficient validity with number needed to harm by 15 people. It can be concluded that night shift work, with duration and certain period could be risk factor for breast cancer in female workers, then further approaches are needed regarding this matter.

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Night Shift Among Women: Is It Associated With Difficulty Conceiving a First Birth?

Frontiers in Public Health ◽

10.3389/fpubh.2020.595943 ◽

2020 ◽

Vol 8 ◽

Author(s):

Renae C. Fernandez ◽

Vivienne M. Moore ◽

Jennifer L. Marino ◽

Melissa J. Whitrow ◽

Michael J. Davies

Keyword(s):

Shift Work ◽

Night Shift ◽

Fertility Treatment ◽

Menstrual Irregularity ◽

Female Reproduction ◽

First Birth ◽

Shift Workers ◽

Night Shift Work ◽

Paid Employment ◽

Increased Risk

Background: Asynchrony in circadian processes alters many physiological systems, including female reproduction. Thus, there are possible reproductive consequences of night shift work for women including menstrual irregularity, endometriosis, and prolonged time to conception. This study examined whether women who worked night shift were more likely than those who did not to require fertility treatment to conceive a first birth, whether they had specific infertility diagnoses, and if such relationships were age-specific.Methods: In a retrospective data linkage study of 128,852 primiparous women, fertility treatment data were linked to the state perinatal registry for South Australia (1986–2002). Potential exposure to night shift work was assessed using a job-exposure matrix. First, the association between night shift work and fertility treatment was assessed among (1) all women, then (2) women in paid employment, using logistic regression. Interactions between age and shift work status were also examined. Secondly, among women who conceived with fertility treatment, we assessed associations between night shift work and type of infertility diagnosis. Potential confounders were considered in all analyses.Results: Among women ≤35 years, night shift workers were more likely to require fertility treatment (all: OR = 1.40, 95% CI 1.19–1.64; in paid employment: OR = 1.27, 95% CI 1.08–1.50). There were no associations among women >35 years. Ethnicity, socioeconomic status and smoking did not affect these results. Among women who underwent fertility treatment, night shift workers were more likely than day workers to have menstrual irregularity (OR = 1.42, 95% CI 1.05–1.91) or endometriosis (OR = 1.34, 95% CI 1.00–1.80).Conclusions: Night shift work may contribute to increased need for fertility treatment in younger women. This increased risk may reflect young women's vulnerability in terms of poor tolerance of night shift work, and/or lack of control and choice about shift schedule.

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Shift work, DNA methylation and epigenetic age

International Journal of Epidemiology ◽

10.1093/ije/dyz027 ◽

2019 ◽

Vol 48 (5) ◽

pp. 1536-1544 ◽

Cited By ~ 9

Author(s):

Alexandra J White ◽

Jacob K Kresovich ◽

Zongli Xu ◽

Dale P Sandler ◽

Jack A Taylor

Keyword(s):

Dna Methylation ◽

Linear Regression ◽

Association Study ◽

Shift Work ◽

Night Shift ◽

Night Shift Work ◽

Age Related ◽

Epigenetic Age ◽

Increased Risk ◽

Epigenetic Age Acceleration

Abstract Background Shift work has been associated with increased risk of age-related morbidity and mortality. Biological age, estimated using DNA methylation (DNAm), may quantify the biological consequences of shift work on the risk of age-related disease. We examined whether prior employment in shift-working occupations was associated with epigenetic age acceleration. Methods In a sample of non-Hispanic White women aged 35–74 (n = 2574), we measured DNAm using the Illumina Infinium Human450 BeadChip and calculated DNAm age using three established epigenetic clocks. Age-acceleration metrics were derived by regressing DNAm age on chronological age and predicting the residuals. Using linear regression, we estimated associations between shift work history and age acceleration. We also conducted an epigenome-wide association study using robust linear-regression models corrected with false discovery rate (FDR) q-values. Results Approximately 7% of women reported any shift work. Higher age acceleration was observed for a 1-year increase in overall [β = 0.11, 95% confidence interval (CI): 0.02–0.21] and night-specific shift work (β = 0.12, 95% CI: 0.03–0.21). The association was strongest for ≥10 years of night shift work (β = 3.16, 95% CI: 1.17–5.15). From the epigenome-wide association study, years of overall and night shift work were associated with DNAm at 66 and 85 CpG sites (FDR < 0.05), respectively. Years of night shift work was associated with lower methylation of a CpG in the gene body of ZFHX3 (cg04994202, q = 0.04), a gene related to circadian rhythm. Conclusions Shift work was associated with differential CpG site methylation and with differential DNAm patterns, measured by epigenetic age acceleration, consistent with long-term negative health effects.

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Rotating night shift work and menopausal age

Human Reproduction ◽

10.1093/humrep/dey390 ◽

2019 ◽

Vol 34 (3) ◽

pp. 539-548 ◽

Cited By ~ 9

Author(s):

D Stock ◽

J A Knight ◽

J Raboud ◽

M Cotterchio ◽

S Strohmaier ◽

...

Keyword(s):

Shift Work ◽

Night Shift ◽

Night Work ◽

Natural Menopause ◽

Night Shift Work ◽

Age At Menopause ◽

Increased Risk ◽

National Cohort ◽

Night Shifts

Abstract STUDY QUESTION How are rotating night shift schedules associated with age at menopause among a large, national cohort of shift working nurses? SUMMARY ANSWER Our findings suggest that working rotating night shifts with sufficient frequency may modestly accelerate reproductive senescence among women who may already be predisposed to earlier menopause. WHAT IS KNOWN ALREADY Younger age at menopause has been associated with increased risk of adverse health outcomes, particularly those linked to reproduction. Night work has been associated with reproductive dysfunction, including disruption of menstrual cycle patterns. STUDY DESIGN, SIZE, DURATION This cohort study was conducted among 80 840 women of the Nurses’ Health Study 2 (NHS2), with prospective follow-up from 1991 through 2013. Loss-to-follow-up of the NHS2 is estimated to be <10%. PARTICIPANTS/MATERIALS, SETTING, METHODS We assessed the association between cumulative and current rotating night shift work and age at natural menopause over 22 years of follow-up (1991–2013). Cox proportional hazards models were used to estimate hazard ratios (HR) for menopause, adjusted for age, smoking status, body mass index, physical activity, alcohol consumption, reproductive factors and exogenous hormone use. MAIN RESULTS AND THE ROLE OF CHANCE Over follow-up, 27 456 women (34%) reached natural menopause. Women who worked 20 or more months of rotating night shifts in the prior 2-year had an increased risk of earlier menopause (multivariable-adjusted (MV)-HR = 1.09, 95% CI: 1.02–1.16) compared to women without rotating night shift work. This risk was stronger among women undergoing menopause or otherwise censored under age 45 years (MV-HR = 1.25, 95% CI: 1.08–1.46), than it was for those continuing in the study when >45 years old (MV-HR = 1.05, 95% CI: 0.99–1.13). Working 10 or more years of cumulative rotating night work was also associated with higher risk of menopause among women reaching menopause under age 45 (MV-HR10–19 years = 1.22, 95% CI: 1.03–1.44; MV-HR≥20 years = 1.73, 95% CI: 0.90–3.35), though not over the age of 45 years (MV-HR10–19 years = 1.04, 95% CI: 0.99–1.10; MV-HR≥20 years = 1.01, 95% CI: 0.89–1.15). LIMITATIONS, REASONS FOR CAUTION The degree to which observed effects of rotating night shifts on age at natural menopause are due to circadian disruption, rather than fatigue and stress associated with working more demanding schedules, is uncertain due to potential residual confounding by these factors. WIDER IMPLICATIONS OF THE FINDINGS This is the first study to assess the effects of night work on menopausal timing among a larger national cohort of shift working women. Women already prone to earlier menopause may further truncate their reproductive lifetime by working schedules comprising day as well as night shifts. STUDY FUNDING/COMPETING INTEREST(s) This study was supported by Center for Disease Control and Prevention/The National Institute for Occupational Safety and Health Grant 5R01OH009803 (PI: Schernhammer E), as well as UM1 CA176726 from the National Institute of Health. The funding sources had no role in the design and conduct of the study; collection, management, analysis and interpretation of the data; preparation, review or approval of the article; and decision to submit the article for publication. The authors have no conflicts of interest.

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Prospective Associations Between Working Time Arrangements and Psychiatric Treatment in Denmark: Protocol for a Cohort Study

JMIR Research Protocols ◽

10.2196/18236 ◽

2020 ◽

Vol 9 (6) ◽

pp. e18236 ◽

Cited By ~ 1

Author(s):

Harald Hannerz ◽

Karen Albertsen ◽

Martin Lindhardt Nielsen ◽

Anne Helene Garde

Keyword(s):

At Risk ◽

Psychiatric Hospital ◽

Shift Work ◽

Study Protocol ◽

Night Shift ◽

Working Hours ◽

Incidence Rates ◽

Hospital Treatment ◽

Long Working Hours ◽

Night Shift Work

Background The burden of mental ill health in working-age populations has prompted research on possible links between work-related factors and mental ill health. Long working hours and night shift work are some of the factors that have been studied in relation to the risk of developing mental ill health. Yet, previous studies have not generated conclusive evidence, and further studies of high quality are needed. Objective This study aims to investigate the prospective association between working time arrangements and mental health in terms of psychotropic drug usage or psychiatric hospital treatment in the general working population of Denmark. Methods Data on total weekly working hours in any job and night shift work from the Danish Labor Force Survey 2000–2013 will be linked to data from the Psychiatric Central Research Register (expected 2400 cases during 700,000 person years at risk) and National Prescription Registry (expected 17,400 cases during 600,000 person years at risk). Participants will be followed for up to 5 years. We will use Poisson regression to separately analyze incidence rates of redeemed prescriptions for psychotropic medicine and incidence rates of psychiatric hospital treatment due to mood disorders, anxiety disorders, or stress-related disorders as a function of weekly working hours and night shift work. The analyses will be controlled for sex, age, calendar time of the interview, and socioeconomic status. Results This is a study protocol. Power calculations indicate that the study has sufficient statistical power to detect relatively small differences in risks and minor interactions (eg, ~90% power to detect a rate ratio of 1.1 for psychoactive medication use). We expect the analyses to be completed by the end of 2020 and the results to be published in 2021. Conclusions In this study protocol, all hypotheses and statistical models of the project have been completely defined before we link the exposure data to the outcome data. The results of the project will indicate to what extent and in what direction the national burden of mental ill health in Denmark has been influenced by long working hours and night shift work. International Registered Report Identifier (IRRID) DERR1-10.2196/18236

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