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Background Shift work can disturb circadian homeostasis and result in fatigue, excessive sleepiness, and reduced quality of life. Light therapy has been shown to impart positive effects in night shift workers. We sought to determine whether or not prolonged exposure to bright light during a night shift reduces sleepiness and enhances psychomotor performance among ICU nurses. Methods This is a single-center randomized, crossover clinical trial at a surgical trauma ICU. ICU nurses working a night shift were exposed to a 10-h period of high illuminance (1500–2000 lx) white light compared to standard ambient fluorescent lighting of the hospital. They then completed the Stanford Sleepiness Scale and the Psychomotor Vigilance Test. The primary and secondary endpoints were analyzed using the paired t test. A p  value <0.05 was considered significant. Results A total of 43 matched pairs completed both lighting exposures and were analyzed. When exposed to high illuminance lighting subjects experienced reduced sleepiness scores on the Stanford Sleepiness Scale than when exposed to standard hospital lighting: mean (sem) 2.6 (0.2) vs. 3.0 (0.2), p  = 0.03. However, they committed more psychomotor errors: 2.3 (0.2) vs. 1.7 (0.2), p  = 0.03. Conclusions A bright lighting environment for ICU nurses working the night shift reduces sleepiness but increases the number of psychomotor errors. Trial registration ClinicalTrials.gov, NCT03331822 . Retrospectively registered on 6 November 2017.

Background: Shift‐work schedules can cause sleep and psychological problems among nurses, negatively affecting their health and quality of life. This trial examined the effects of low‐energy light therapy on sleep, psychological symptoms, and heart rate variability among shift‐work nurses. Methods: This randomized controlled trial was conducted from July 2021 to June 2022. The inclusion criteria were nurses with self‐reported insomnia who worked in shifts in the last 6 months in a medical center in northern Taiwan. Block randomization was used to assign the study participants to two groups: experimental ( n = 32) and control ( n = 32). A portable Meridian Aura Cap equipped with a low‐level light‐emitting diode was used to provide red and near‐infrared light (660 and 850 nm) for 30 min, three times a week for 4 weeks; the control group did not receive any intervention. The Depression Anxiety Stress Scale‐21 and Insomnia Severity Index were used to measure psychological symptoms and sleep problems, respectively. Heart rate variability was measured by the ANSWatch. Results: No significant differences were reported in preintervention scores. After the 4‐week intervention, the intervention group scored significantly lower in insomnia (4.3 vs. 12.6, respectively; p < 0.001), depression (2.5 vs. 7.9, p < 0.001), anxiety (3.1 vs. 9.2, p < 0.001), and stress (5.6 vs. 12, p < 0.001) than those in the controls. No significant differences were observed in heart rate variability between the two groups. Conclusion: Low‐level light‐emitting diode light therapy improved sleep quality in shift‐work nurses with insomnia and alleviated depression, anxiety, and stress symptoms; however, it did not improve heart rate variability, possibly because of the short intervention duration and the ongoing shift‐work schedule. Implications for Nursing Management: Employers could consider providing phototherapy for shift nurses to improve their health. Trial Registration: ClinicalTrials.gov identifier: NCT05146596

Night shift work can associate with an increased risk for depression. As night workers experience a ‘misalignment’ between their circadian system and daily sleep–wake behaviors, with negative health consequences, we investigated whether exposure to circadian misalignment underpins mood vulnerability in simulated shift work. We performed randomized within-subject crossover laboratory studies in non-shift workers and shift workers. Simulated night shifts were used to induce a misalignment between the endogenous circadian pacemaker and sleep/wake cycles (circadian misalignment), while environmental conditions and food intake were controlled. Circadian misalignment adversely impacted emotional state, such that mood and well-being levels were significantly decreased throughout 4 days of continuous exposure to circadian misalignment in non-shift workers, as compared to when they were under circadian alignment (interaction of “circadian alignment condition” vs. “day”, mood: p  < 0.001; well-being: p  < 0.001; adjusted p -values). Similarly, in shift workers, mood and well-being levels were significantly reduced throughout days of misalignment, as compared to circadian alignment (interaction of “circadian alignment condition” vs. “day”, mood: p  = 0.002; well-being: p  = 0.002; adjusted p -values). Our findings indicate that circadian misalignment is an important biological component for mood vulnerability, and that individuals who engage in shift work are susceptible to its deleterious mood effects.

ObjectivesA decreased ability to repair oxidative DNA damage, due to melatonin suppression, is a compelling mechanism by which night shift workers are at an increased risk of cancer. We sought to determine if melatonin supplementation would improve oxidative DNA damage repair among night shift workers.MethodsWe conducted a parallel-arm randomised placebo-controlled trial of melatonin supplementation among 40 night shift workers. Supplements were consumed before engaging in day sleep over a 4-week period. All urine excreted during a representative day sleep and night work period before and during the intervention period was collected for measurement of creatinine-adjusted 8-hydroxy-2′-deoxyguanosine (8-OH-dG) as an indicator of oxidative DNA damage repair capacity, with higher concentrations indicating better repair. Linear regression models were used to analyse the association between ln-transformed 8-OH-dG concentration and intervention status during day sleep and night work.ResultsThe melatonin intervention was associated with a borderline statistically significant 1.8-fold increase in urinary 8-OH-dG excretion during day sleep (95% CI 1.0, 3.2, p=0.06). No statistically significant difference in 8-OH-dG excretion was observed during the subsequent night shift (melatonin vs placebo excretion ratio=0.9; 95% CI 0.6, 1.5; p=0.7).ConclusionsOur results suggest that melatonin supplementation improves oxidative DNA damage repair capacity among night shift workers. Future larger-scale trials are needed to evaluate the impact of varying doses of melatonin supplements and examine the impacts of longer-term use of melatonin supplements by night shift workers.

Effective countermeasures against the adverse cardiovascular effects of circadian misalignment, such as effects experienced due to night work or jet lag, remain to be established in humans. Here, we aim to test whether eating only during daytime can mitigate such adverse effects vs. eating during the night and day (typical for night shift workers) under simulated night work (secondary analysis of NCT02291952). This single-blind, parallel-arm trial randomized 20 healthy participants (non-shift workers) to simulated night work with meals consumed during night and day (Nighttime Meal Control Group) or only during daytime (Daytime Meal Intervention Group). The primary outcomes were pNN50 (percentage consecutive heartbeat intervals >50 ms), RMSSD (root mean square of successive heartbeat differences), and LF/HF (low/high cardiac frequency). The secondary outcome was blood concentrations of prothrombotic factor plasminogen activator inhibitor-1 (PAI-1). These measures were assessed under Constant Routine conditions, before (baseline) and after (postmisalignment) simulated night work. The meal timing intervention significantly modified the impact of simulated night work on cardiac vagal modulation and PAI-1 ( p FDR = 0.001). In the Control Group, the postmisalignment Constant Routine showed a decrease in p NN50 by 25.7% ( p FDR = 0.008) and RMMSD by 14.3% ( p FDR = 0.02), and an increase in LF/HF by 5.5% ( p FDR = 0.04) and PAI-1 by 23.9% ( p FDR = 0.04), vs. the baseline Constant Routine. In the Intervention Group, there were no significant changes in these outcomes. For exploratory outcomes, the intervention significantly modified the impact of simulated night work on blood pressure ( P < 0.05), with no significant change in the Control Group, and a significant reduction by 6-8% ( P < 0.01) in the Intervention Group; without significant effects for heart rate or cortisol. These findings indicate that daytime eating, despite mistimed sleep, may mitigate changes in cardiovascular risk factors and offer translational evidence for developing a behavioral strategy to help minimize the adverse changes in cardiovascular risk factors in individuals exposed to circadian misalignment, such as shift workers. Circadian misalignment, which typically occurs in shift work, associates with cardiovascular diseases. Here the authors report that eating only in the daytime during simulated night work mitigates adverse changes in cardiovascular risk factors (including autonomic cardiac control, prothrombotic factor, and blood pressure) in a secondary analysis of a randomized controlled trial.

ObjectiveObservational studies indicate an association between working nights and miscarriage, but inaccurate exposure assessment precludes causal inference. Using payroll data with exact and prospective measurement of night work, the objective was to investigate whether working night shifts during pregnancy increases the risk of miscarriage.MethodsA cohort of 22 744 pregnant women was identified by linking the Danish Working Hour Database (DWHD), which holds payroll data on all Danish public hospital employees, with Danish national registers on births and admissions to hospitals (miscarriage). The risk of miscarriage during pregnancy weeks 4–22 according to measures of night work was analysed using Cox regression with time-varying exposure adjusted for a fixed set of potential confounders.ResultsIn total 377 896 pregnancy weeks (average 19.7) were available for follow-up. Women who had two or more night shifts the previous week had an increased risk of miscarriage after pregnancy week 8 (HR 1.32 (95% CI 1.07 to 1.62) compared with women, who did not work night shifts. The cumulated number of night shifts during pregnancy weeks 3–21 increased the risk of miscarriages in a dose-dependent pattern.ConclusionsThe study corroborates earlier findings that night work during pregnancy may confer an increased risk of miscarriage and indicates a lowest observed threshold level of two night shifts per week.

Abstract Study Objectives: Fatigue from sleep loss is a risk to physician and patient safety, but objective data on physician sleep and alertness on different duty hour schedules is scarce. This study objectively quantified differences in sleep duration and alertness between medical interns working extended overnight shifts and residents not or rarely working extended overnight shifts. Methods: Sleep–wake activity of 137 interns and 87 PGY-2/3 residents on 2-week Internal Medicine and Oncology rotations was assessed with wrist-actigraphy. Alertness was assessed daily with a brief Psychomotor Vigilance Test (PVT) and the Karolinska Sleepiness Scale. Results: Interns averaged 6.93 hours (95% confidence interval [CI] 6.84–7.03 hours) sleep per 24 hours across shifts, significantly less than residents not working overnight shifts (7.18 hours, 95% CI 7.06–7.30 hours, p = .007). Interns obtained on average 2.19 hours (95% CI 2.02–2.36 hours) sleep during on-call nights (17.5% obtained no sleep). Alertness was significantly lower on mornings after on-call nights compared to regular shifts (p < .001). Naps between 9 am and 6 pm on the first day post‐call were frequent (90.8%) and averaged 2.84 hours (95% CI 2.69–3.00 hours), but interns still slept 1.66 hours less per 24 hours (95% CI 1.56–1.76 hours) compared to regular shift days (p < .001). Sleep inertia significantly affected alertness in the 60 minutes after waking on-call. Conclusions: Extended overnight shifts increase the likelihood of chronic sleep restriction in interns. Reduced levels of alertness after on-call nights need to be mitigated. A systematic comparison of sleep, alertness, and safety outcomes under current and past duty hour rules is encouraged.

OBJECTIVE: This study aimed to (i) investigate associations between different characteristics of exposure to shift work and breast cancer risk and (ii) identify effect modifiers. METHODS: Comprising 42 379 women from the Finnish Public Sector cohort, this longitudinal study included data from survey responses, payroll-based working hour records, and national breast cancer registry data. Cause-specific Cox proportional hazards models were used to estimate hazard ratios (HR), adjusting for age, marital status, socioeconomic status, living with a child, lifestyle, and occupational factors. Stratified analyses and interaction tests were performed to assess effect modification. RESULTS: Over an average follow-up of 9.8 years, 945 women were diagnosed with breast cancer. Among women aged ≥50 years, increased risk was associated with working >3 consecutive night shifts [hazard ratio (HR) 1.64, 95% confidence interval (CI) 1.22–2.21] and evening shifts (HR 1.28, 95% CI 1.03–1.59). Sleep problems and fatigue at work modified the association between night shift work and breast cancer risk, whereas psychological distress and diurnal preference did not. Permanent night shift workers reporting sleep problems (HR 1.76, 95% CI 1.01–3.09) or fatigue at work (HR 1.90, 95% CI 1.08–3.35) had a higher risk compared to day workers with similar symptoms. CONCLUSIONS: Women aged ≥50 years showed increased breast cancer risk for several shift work characteristics. Permanent night shift work was especially associated with increased risk among those reporting sleep problems or fatigue. These findings may help identify groups needing closer occupational health monitoring, though causal inference is limited by the observational design. Intervention studies are required to determine whether changes in work schedules or management of sleep problems and fatigue could reduce risk.

ObjectivesWe sought to evaluate whether rotating night shift work increases the risk of type 2 diabetes, particularly among women with a history of gestational diabetes mellitus (GDM).MethodsWe included 50 122 Nurses’ Health Study II participants who were parous at baseline in 1989 or at any time during follow-up through 2019. Using multivariable-adjusted Cox proportional hazards models, we estimated the HRs and 95% CIs for the associations between cumulative years of rotating night shift work and incident type 2 diabetes, overall, and by history of GDM.ResultsCompared with participants who never engaged in rotating night shift work, we observed a graded increase in the risk of type 2 diabetes with cumulative years of rotating night shift work: HR (95% CI) 1.14 (1.04 to 1.24) for <5 years, 1.32 (1.17 to 1.49) for 5–10 years and 1.32 (1.16 to 1.50) for >10 years (p-linear trend <0.001). Stratifying by history of GDM, we observed a similar pattern of associations among participants without a history of GDM, but not among those with a history of GDM (p-interaction=0.02). History of GDM was strongly associated with risk of incident type 2 diabetes in all women, including those who never worked rotating night shifts: HR (95% CI) 4.76 (3.90 to 5.81).Conclusions/interpretationCumulative years of rotating night shift work were modestly associated with a higher risk of type 2 diabetes, overall, and among nurses without a history of GDM. Rotating night shift work was not associated with risk of type 2 diabetes among individuals with a history of GDM, an exceptionally high-risk subgroup for type 2 diabetes.

Abstract A high proportion (20%–30%) of shift workers experience Shift Work Disorder (SWD), characterized by chronic sleepiness and/or insomnia associated with work schedules. The reasons for individual variation in shift work tolerance are not well understood, however. The aim of this study was to identify individual factors that contribute to the risk of SWD. Nurses (n = 202) were categorized as low or high risk of SWD based on the Shift Work Disorder Questionnaire. Participants provided demographic and lifestyle information and completed the Sleep Hygiene Index (SHI) and Morningness–Eveningness Questionnaire (MEQ). High risk of SWD was associated with poorer sleep hygiene (SHI, 35.41 ± 6.19 vs. 31.49 ± 7.08, p < .0001) and greater eveningness (MEQ, 34.73 ± 6.13 vs. 37.49 ± 6.45, p = .005) compared to low risk. No other factors, including body mass index, marital status, having children, or caffeine or alcohol intake were significant. Logistic regression showed that SHI was the most significant contributing factor to SWD risk (odds ratio [OR] = 1.09, 95% confidence interval [CI] = 1.04 to 1.14). Standardized odds ratio further revealed that with every unit increase on the SHI score, the odds of being at high risk of SWD increased by 80% (OR = 1.84). Most individuals at high risk of SWD reported “always” or “frequently” going to bed at different times (79%) and waking at different times (83%; compared to 58%, p = .017, and 61%, p = .002, respectively for the low-risk group), as well as going to bed stressed/angry (67% vs. 41%, p < .0001) and/or planning/worrying in bed (54% vs. 22%, p < .0001). Interventions aimed at improving sleep hygiene practices and psychological health of shift workers may help reduce the risk of SWD.