It is a general assumption that the prospective cohort study design is the gold standard approach and is superior to the case-control study design in epidemiology. However, there may be exceptions if the exposure is complex and requires collection of detailed information on many different aspects. Night-shift work, which impairs circadian rhythms, is an example of such a complex occupational exposure and may increase the risks of breast, prostate, and colorectal cancer. So far, for logistical reasons, investigators in cohort studies have assessed shift work rather crudely, lacking information on full occupational history and relevant shift-work metrics, and have presented mostly null findings. On the other hand, most cancer case-control studies have assessed the lifetime occupational histories of participants, including collection of detailed night-shift work metrics (e.g., type, duration, intensity), and tend to show positive associations. In this commentary, we debate why cohort studies with weak exposure assessment and other limitations might not necessarily be the preferred or less biased approach in assessing the carcinogenicity of night-shift work. Furthermore, we propose that risk-of-bias assessment and comparison of associations between studies with low versus high risks of bias be considered in future synthesis of the evidence.

OBJECTIVE: To investigate the association of hospital physicians\' working hours and on-call shifts with the risk of occupational injuries.
METHODS: In this nested cohort study of 556 Finnish hospital physicians, we linked electronic records from working-hour and on-call duty payroll data to occupational injury data obtained from the Finnish Workers\' Compensation Center for the period 2005-2019. We used a case-crossover design with matched intervals for a 7-day \'case window\' immediately prior to occupational injury and a \'control window\' 7 days prior to the beginning of the case window, and analyzed their associations using conditional logistic regression models.
RESULTS: We noted 556 occupational injuries, 281 at the workplace and 275 while commuting. Having three to four long (>12 h) work shifts on the preceding 7 days was associated with a higher probability of an occupational injury (odds ratio [OR] 2.14, 95% confidence interval [CI] 1.11, 4.09), and the OR for three to four on-call shifts was 3.54 (95%CI 2.11, 5.92) in comparison to having none of these work shift types. A higher number of several consecutive working days was associated with a higher probability of injury in a dose-response manner. Moreover, increasing weekly working hours was associated with an increased likelihood of injury (OR 1.03, 95%CI 1.01, 1.04), whereas the number of normal (≤12 h) work shifts reduced this likelihood (OR 0.79, 95%CI 0.64, 0.98).
CONCLUSIONS: Our findings suggest that accumulated working-hour load, as opposed to single, very long (>24 h) work shifts, may increase the risk of occupational injury among hospital physicians.

BACKGROUND: Blood glucose is higher in people working night shifts compared to day workers. Changes to eating behaviour, activity and sleep patterns in addition to circadian disruption are likely to impact glucose management in night-shift workers with type 2 diabetes.
OBJECTIVE: To investigate current dietary intake and glucose variability during night work, including barriers and facilitators to dietary behaviour in this context.
METHODS: A mixed-methods case study will be conducted. Shift workers with type 2 diabetes working in a hospital setting will be recruited to this two-part study. Part 1: 70 participants will complete a 10-day observational study collecting data on continuous glucose, diet (self-report diary), sleep and physical activity during a period covering night work, rest days and non-night workdays. Mean glucose concentration and variability, and the mean healthy diet index score, will be compared between days of night work, non-night work and rest, after adjusting for other individual factors (sleep/physical activity/demographics). Part 2: A sample (n~13) will complete semi-structured interviews based on behavioural science frameworks to explore barriers/enablers to dietary behaviour when working night shifts. This will inform a quantitative survey to explore the generalisability of interview findings.
CONCLUSIONS: Findings from Part 1 and 2 will be triangulated to identify potential intervention strategies to address key barriers and enablers to healthier eating, and in turn improved glucose control, in shift workers with type 2 diabetes. This will be facilitated through stakeholder consultation and application of behavioural science frameworks. Shift-Diabetes study registration: ISRCTN11764942.

Recent evidence indicates that disrupted sleep could contribute to the development of Alzheimer\'s disease by influencing the production and/or clearance of the amyloid-β protein. We set up a case-control study to investigate the association between long-term work-induced sleep disruption, cognitive function, and brain amyloid-β burden.
Nineteen male maritime pilots (aged 48-60 years) with chronic work-related sleep disruption and a sex-, age-, and education-matched control sample (n = 16, aged 50-60 years) with normal sleep completed the study. Primary sleep disorders were ruled out with in-lab polysomnography. Additional sleep measurements were obtained at home using actigraphy, sleep-wake logs, and a single-lead EEG device. Cognitive function was assessed with a neuropsychological test battery, sensitive to early symptomatic Alzheimer\'s disease. Brain amyloid-β burden was assessed in maritime pilots using 18F-flutemetamol amyloid PET-CT.
Maritime pilots reported significantly worse sleep quality (Pittsburgh Sleep Quality Index (PSQI) = 8.8 ± 2.9) during work weeks, compared to controls (PSQI = 3.2 ± 1.4; 95% CI 0.01 to 2.57; p = 0.049). This was confirmed with actigraphy-based sleep efficiency (86% ± 3.8 vs. 89.3% ± 4.3; 95% CI 0.43 to 6.03; p = 0.03). Home-EEG recordings showed less total sleep time (TST) and deep sleep time (DST) during work weeks compared to rest weeks (TST 318.56 (250.21-352.93) vs. TST 406.17 (340-425.98); p = 0.001; DST 36.75 (32.30-58.58) vs. DST 51.34 (48.37-69.30); p = 0.005)). There were no differences in any of the cognitive domains between the groups. For brain amyloid-β levels, mean global cortical standard uptake value ratios of 18F-flutemetamol were all in the normal range (1.009 ± 0.059; 95% CI 0.980 to 1.037), confirmed by visual reads.
Capitalizing on the particular work-rest schedule of maritime pilots, this study with a small sample size observed that long-term intermittent sleep disruption had no effects on global brain amyloid-β levels or cognitive function.

Extended shifts are common in medical practice. This is when doctors are required to work continuously for more than 16 h, with little or no rest, often without a maximum limit. These shifts have been a part of medical practice for more than a century. Research on the impact of fatigue presents compelling evidence that extended shifts increase the risk of harm to patients and practitioners. However, where the number of doctors is limited and their workloads are not easily reduced, there are numerous barriers to reform. Some of these include a perceived lack of safer alternatives, concerns about continuity of care, trainee education, and doctors\' preferences. As such, working hour reorganisation has been contentious globally. South Africa, a middle-income country where extended shifts are unregulated for most doctors, offers a useful case study of reform efforts. The South African Safe Working Hours campaign has promoted working hour reorganization through multi-level advocacy efforts, although extended shifts remain common. We propose that extended shifts should be regarded as an occupational hazard under health and safety legislation. We suggest options for managing the risks of extended shifts by adapting the hierarchy of controls for occupational hazards. Despite the challenges reform pose, the practice of unregulated extended shifts should not continue.

We present a case report of 2 migraine patients engaged in shift work, followed by a narrative review, to assess whether shift work influences headache-related disability and chronification of migraine.
Numerous modifiable factors can lead to chronification of migraine and to higher headache-related disability. These include, among others, obesity, depression, overuse of acute medications, ineffective acute treatments, and stressful life events. Sleep disruptions and disorders are also felt to increase the risk of transitioning from episodic to chronic migraine. We hypothesize that shift work, which by definition leads to atypical or irregular sleep cycles, along with poor quality sleep, is a risk factor for chronification of migraine.
We present the case histories of 2 shift workers with migraine as per International Classification of Headache Disorders 3 criteria, seen at a large, busy academic headache center, followed by a narrative review of the literature.
Previous literature regarding the relationship between shift work and migraine is sparse and conflicting, with more recent studies suggesting that shift work may be a risk factor for migraine-related disability. In our case series, both patients initially reported severe migraine headache-related disability and both patients had noted a worsening of their headaches after beginning night shift work. Both improved when switched back to day shifts, then worsened upon being put back on night shifts. Their headache patterns finally reverted from chronic to episodic migraine after eliminating night shifts completely and maintaining a good sleep routine.
In the 2 cases presented, shift work appeared to be associated with chronification of migraine and higher headache-related disability despite optimal headache management and good patient adherence. A switch to only day shifts promoted transition to an episodic, less disabling pattern of migraine. It is clinically important to take a detailed sleep history in headache patients, and when appropriate, provide support for workplace accommodations. Further larger-scale, rigorous studies are needed to more clearly delineate the relationship between shift work and migraine.

Successful pregnancy requires adaptation in maternal physiology. During intrauterine life the mother\'s circadian timing system supports successful birth and postnatal development. Maternal melatonin is important to transmit circadian timing and day length to the fetus. This study aims to describe the third trimester of pregnancy among day (n = 5) and night (n = 3) workers by assessing their melatonin levels in a natural environment. Additionally, we describe the worker\'s metabolic profiles and compare the health status of the newborns between groups of day and night working mothers. Our results indicate an occurrence of assisted delivery (cesarean and forceps) among night workers. Moreover, the newborns of night workers showed lower Apgar index and breastfeeding difficulty indicating a worse condition to deal with the immediate outside the womb environment. Additionally, there was lower night-time melatonin production among pregnant night workers compared to day workers. These findings may be related to light-induced suppression of melatonin that occurs during night work. We conclude that night work and consequent exposure to light at unconventional times might compromise the success of pregnancy and the health of the newborn. Further studies need to be carried out to monitor pregnancy and newborn health in pregnant night workers.

BACKGROUND: Shift work characteristics, such as the number of night shifts or quick returns, are linked to disturbed sleep and greater work-life conflict, but little is known about their association with short sickness absences. Studies utilizing objective working-hour characteristic data can provide knowledge on specific shift work characteristics that may associate with sick leave. We investigated the association between working-hour characteristics in shift work and the incidence of short (1-3 days) sickness absences.
METHODS: The individual-level data were collected from the employers\' electronic working time records of the Finnish Public Sector study. The final analytical sample was restricted to the first incidence of short sickness absence (1-3 days) from January 1, 2008 to the end of 2015. We studied employees with shift work contracts (n = 12 156) and day work contracts (n = 6225). Of these, 89% were female workers, with a mean age of 37.1 years, and 12% worked part-time. We calculated type of shift (morning, day, evening, and night), quick returns (< 11 h between two work shifts), length of work shift and weekly working time. We utilized case-crossover study design to compare the working-hour characteristics of the 28 days preceding sickness absence (exposure window) and those of the 28 days before the exposure window (control window), using conditional logistic regression models for odds ratios with 95% Confidence Intervals (95%CI).
RESULTS: Exposure to ≥ 2, and especially ≥ 4 consecutive night shifts associated with an increased likelihood of short sickness absence (OR 1.24, 95%CI 1.12-1.38 and OR 1.54, 95%CI 1.10-2.15, respectively) among shift workers, whereas a high number (> 25%) of evening shifts and having ≥ 2 consecutive evening shifts associated with lower odds of sickness absence. Over 40-hour weeks (OR 1.29, 95%CI 1.20-1.39), over 48-hour weeks (OR 1.24, 95%CI 1.01-1.54) and quick returns (OR 1.02, 95%CI 1.01-1.02) increased the likelihood of sickness absence. Having only a few (0-1 or 2-3) quick returns over 28 days decreased the likelihood of sickness absence (ORs 0.46 and 0.67), whereas having ≥ 5 quick returns over 28 days increased it (OR 1.88, 95%CI 1.76-1.99). These associations were similar among both shift and day workers.
CONCLUSIONS: Long working hours, several consecutive night shifts and quick returns increase the risk of short sickness absence. These working-hour characteristics should be avoided in shift scheduling to minimize sickness absence and increased costs for the employer.

Research indicates that shiftwork may be associated with increased risks of adverse health outcomes, including some cancers. However, the evidence of an association between shiftwork and colorectal cancer risk is limited and inconclusive. Further, while several possible pathways through which shiftwork might result in cancer have been proposed, few studies have taken these factors into account. We investigated the association between two types of shiftwork (graveyard shiftwork and early-morning shiftwork) and six mechanistic shiftwork variables (including light at night and phase shift) and the risk of colorectal cancer among females in an Australian population-based case-control study. Graveyard shiftwork was the primary exposure of interest.
Participants (350 cases and 410 controls) completed a lifetime occupational history, and exposure to each of the eight shiftwork variables was assigned to participants through a job exposure matrix. We used logistic regression to calculate odds ratios (OR) and corresponding 95% confidence intervals (CI) for the association between different shiftwork variables and the risk of colorectal cancer, adjusting for potential demographic, lifestyle and medical confounders.
Working in an occupation involving long-term exposure (>7.5 years) to graveyard shiftwork was not associated with colorectal cancer risk (adjusted OR 0.95, 95% CI 0.57 to 1.58). Similarly, no increased risks of colorectal cancer were seen for any of the other seven shiftwork variables examined.
No evidence of an increased risk of colorectal cancer among females who had worked in occupations involving shiftwork was observed in this study.

The first case of video-polysomnography (vPSG) documented sleep masturbation in a male is reported, and the second reported case of shift work induced sexsomnia. A 20 y.o. soldier with childhood sleepwalking (SW) developed sleep masturbation and SW triggered by military shift work. vPSG documented two episodes of sleep masturbation from N2 sleep in the fourth sleep cycle and from N3 sleep during the fifth sleep cycle. There was no sleep-disordered breathing nor periodic limb movements. vPSG thus confirmed confusional arousals from NREM sleep as the cause of the masturbation. Bedtime clonazepam therapy controlled the SW but not the masturbation.