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Working from home has become standard for employees with a university degree. The most common scheme, which has been adopted by around 100 million employees in Europe and North America, is a hybrid schedule, in which individuals spend a mix of days at home and at work each week 1 , 2 . However, the effects of hybrid working on employees and firms have been debated, and some executives argue that it damages productivity, innovation and career development 3 , 4 – 5 . Here we ran a six-month randomized control trial investigating the effects of hybrid working from home on 1,612 employees in a Chinese technology company in 2021–2022. We found that hybrid working improved job satisfaction and reduced quit rates by one-third. The reduction in quit rates was significant for non-managers, female employees and those with long commutes. Null equivalence tests showed that hybrid working did not affect performance grades over the next two years of reviews. We found no evidence for a difference in promotions over the next two years overall, or for any major employee subgroup. Finally, null equivalence tests showed that hybrid working had no effect on the lines of code written by computer-engineer employees. We also found that the 395 managers in the experiment revised their surveyed views about the effect of hybrid working on productivity, from a perceived negative effect (−2.6% on average) before the experiment to a perceived positive one (+1.0%) after the experiment. These results indicate that a hybrid schedule with two days a week working from home does not damage performance. A trial investigating the effects of a hybrid working schedule in a Chinese technology firm in 2021–2022 shows that working from home two days a week improved job satisfaction, reduced quitting and did not affect performance.

Shift work is a risk factor for hypertension, inflammation, and cardiovascular disease. This increased risk cannot be fully explained by classic risk factors. One of the key features of shift workers is that their behavioral and environmental cycles are typically misaligned relative to their endogenous circadian system. However, there is little information on the impact of acute circadian misalignment on cardiovascular disease risk in humans. Here we show—by using two 8-d laboratory protocols—that short-term circadian misalignment (12-h inverted behavioral and environmental cycles for three days) adversely affects cardiovascular risk factors in healthy adults. Circadian misalignment increased 24-h systolic blood pressure (SBP) and diastolic blood pressure (DBP) by 3.0 mmHg and 1.5 mmHg, respectively. These results were primarily explained by an increase in blood pressure during sleep opportunities (SBP, +5.6 mmHg; DBP, +1.9 mmHg) and, to a lesser extent, by raised blood pressure during wake periods (SBP, +1.6 mmHg; DBP, +1.4 mmHg). Circadian misalignment decreased wake cardiac vagal modulation by 8–15%, as determined by heart rate variability analysis, and decreased 24-h urinary epinephrine excretion rate by 7%, without a significant effect on 24-h urinary norepinephrine excretion rate. Circadian misalignment increased 24-h serum interleukin-6, C-reactive protein, resistin, and tumor necrosis factor-α levels by 3–29%. We demonstrate that circadian misalignment per se increases blood pressure and inflammatory markers. Our findings may help explain why shift work increases hypertension, inflammation, and cardiovascular disease risk.

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.

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.

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.

Abstract Study Objectives Shiftwork is associated with cognitive impairment and reduced sleep time and quality, largely due to circadian misalignment. This study tested if circadian-informed lighting could improve cognitive performance and sleep during simulated night shifts versus dim control lighting. Methods Nineteen healthy participants (mean ± SD 29 ± 10 years, 12 males, 7 females) were recruited to a laboratory study consisting of two counterbalanced 8-day lighting conditions (order randomized) 1-month apart: (1) control lighting condition - dim, blue-depleted and (2) circadian-informed lighting condition - blue-enriched and blue-depleted where appropriate. Participants underwent an adaptation night (22:00–07:00 hours), then four nights of simulated night work (cognitive testing battery of nine tasks, 00:00–08:00 hours), and sleep during the day (10:00–19:00 hours). Psychomotor vigilance task (PVT) lapses, Karolinska Sleepiness Scale (KSS) scores, and polysomnography-derived sleep outcomes were compared between conditions and across days using mixed models. Results Significant condition-by-day-by-time of task interaction effects were found for PVT lapses, median reaction time, and reaction speed, with ~50% fewer lapses by the end of simulated shift work with circadian-informed lighting versus control (mean ± SD 7.4 ± 5.0 vs. 15.6 ± 6.1). KSS was lower around the night shift midpoints on days 6 and 7 with circadian versus control lighting. Participants slept 52 minutes longer [95% CIs: 27.5, 76.5 minutes] by day 7 with circadian-informed versus control lighting, p < .001. Effects were inconsistent on other performance tasks. Conclusions Circadian-informed lighting improved sleep, sleepiness, and vigilance compared to control lighting. These findings support the potential for lighting interventions to improve sleep and vigilance in night shift workers chronically exposed to dim lighting. Graphical Abstract Graphical Abstract

Abstract Study Objective Night work has detrimental impacts on sleep and performance, primarily due to misalignment between sleep–wake schedules and underlying circadian rhythms. This study tested whether circadian-informed lighting accelerated circadian phase delay, and thus adjustment to night work, compared to blue-depleted standard lighting under simulated submariner work conditions. Methods Nineteen healthy sleepers (12 males; mean ± SD aged 29 ± 10 years) participated in two separate 8-day visits approximately 1 month apart to receive, in random order, circadian-informed lighting (blue-enriched and dim, blue-depleted lighting at specific times) and standard lighting (dim, blue-depleted lighting). After an adaptation night (day 1), salivary dim-light melatonin onset (DLMO) assessment was undertaken from 18:00 to 02:00 on days 2–3. During days 3–7, participants completed simulated night work from 00:00 to 08:00 and a sleep period from 10:00 to 19:00. Post-condition DLMO assessment occurred from 21:00 to 13:00 on days 7–8. Ingestible capsules continuously sampled temperature to estimate daily core body temperature minimum (Tmin) time. Tmin and DLMO circadian delays were compared between conditions using mixed effects models. Results There were significant condition-by-day interactions in Tmin and DLMO delays (both p < .001). After four simulated night shifts, circadian-informed lighting produced a mean [95% CI] 5.6 [3.0 to 8.2] hours greater delay in Tmin timing and a 4.2 [3.0 to 5.5] hours greater delay in DLMO timing compared to standard lighting. Conclusions Circadian-informed lighting accelerates adjustment to shiftwork in a simulated submariner work environment. Circadian lighting interventions warrant consideration in any dimly lit and blue-depleted work environments where circadian adjustment is relevant to help enhance human performance, safety, and health.

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.

Abstract Study objectives To investigate the effect of a work schedule with abated quick returns (i.e. > 11 hours between two shifts) on insomnia, daytime sleepiness, and work-related fatigue compared to a shift schedule maintaining the usual number of quick returns. Methods A two-armed cluster randomized controlled trial including 66 units was conducted at a university hospital in Norway. Units with healthcare workers on rotating shift schedules were randomly assigned to a shift schedule with abated quick returns (intervention) or to continue with a schedule including quick returns as usual (control) for 6 months. Questionnaires assessed symptoms of insomnia (Bergen Insomnia Scale [BIS]), daytime sleepiness (Epworth Sleepiness Scale [ESS]), and work-related fatigue (Revised Swedish Occupational Fatigue Inventory) at baseline and towards the end of the intervention. Data were analyzed using multilevel linear mixed-effects models, and Cohen’s d was used to calculate the effect size between groups. Results Overall, 1314 healthcare workers (85.2% female) completed the baseline questionnaire (response rate 49.1%), and 552 completed the follow-up questionnaire. The intervention reduced quick returns from an average of 13.2 (SD = 8.7) to 6.7 (SD = 6.0), while the control group’s average remained relatively unchanged from 13.2 (SD = 8.7) to 12.0 (SD = 9.3). Results showed a small improvement in symptoms of insomnia (BIS; d = −0.13, p = .022) and daytime sleepiness (ESS; d = −0.14, p = .013) in favor of the intervention. No effects were observed on work-related fatigue. Conclusions Reducing the number of quick returns in the work schedule resulted in improvements in insomnia and daytime sleepiness. The findings highlight the importance of sufficient daily rest time in the work schedule of healthcare workers. Clinical Trial Health Promoting Work Schedules: The Effect of Abolishing Quick Returns (HeWoS); clinicaltrials.gov/ct2/show/NCT04693182; Registered at ClinicalTrials.gov with the identifier NCT04693182. Graphical Abstract Graphical Abstract

We compared resident physician work hours and sleep in a multicenter clustered-randomized crossover clinical trial that randomized resident physicians to an Extended Duration Work Roster (EDWR) with extended-duration (≥24 hr) shifts or a Rapidly Cycling Work Roster (RCWR), in which scheduled shift lengths were limited to 16 or fewer consecutive hours. Three hundred two resident physicians were enrolled and completed 370 1 month pediatric intensive care unit rotations in six US academic medical centers. Sleep was objectively estimated with wrist-worn actigraphs. Work hours and subjective sleep data were collected via daily electronic diary. Resident physicians worked fewer total hours per week during the RCWR compared with the EDWR (61.9 ± 4.8 versus 68.4 ± 7.4, respectively; p < 0.0001). During the RCWR, 73% of work hours occurred within shifts of ≤16 consecutive hours. In contrast, during the EDWR, 38% of work hours occurred on shifts of ≤16 consecutive hours. Resident physicians obtained significantly more sleep per week on the RCWR (52.9 ± 6.0 hr) compared with the EDWR (49.1 ± 5.8 hr, p < 0.0001). The percentage of 24 hr intervals with less than 4 hr of actigraphically measured sleep was 9% on the RCWR and 25% on the EDWR (p < 0.0001). RCWRs were effective in reducing weekly work hours and the occurrence of >16 consecutive hour shifts, and improving sleep duration of resident physicians. Although inclusion of the six operational healthcare sites increases the generalizability of these findings, there was heterogeneity in schedule implementation. Additional research is needed to optimize scheduling practices allowing for sufficient sleep prior to all work shifts.Clinical Trial: Multicenter Clinical Trial of Limiting Resident Work Hours on ICU Patient Safety (ROSTERS), https://clinicaltrials.gov/ct2/show/NCT02134847.