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Tracey L Sletten,1 Bhairavi Raman,1 Michelle Magee,1 Sally A Ferguson,2 David J Kennaway,3 Ronald R Grunstein,4,5 Steven W Lockley,6,7 Shantha MW Rajaratnam1,6,7 1Turner Institute for Brain and Mental Health, School of Psychological Sciences, Monash University, Melbourne, Victoria, Australia; 2Central Queensland University, Appleton Institute, Goodwood, SA, Australia; 3Robinson Research Institute, School of Medicine, Discipline of Obstetrics and Gynaecology, University of Adelaide, Adelaide, SA, Australia; 4Woolcock Institute of Medical Research, University of Sydney, Sydney, NSW, Australia; 5Department of Respiratory & Sleep Medicine, Royal Prince Alfred Hospital, Sydney, NSW, Australia; 6Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women’s Hospital, Boston, MA, USA; 7Division of Sleep Medicine, Harvard Medical School, Boston, MA, USACorrespondence: Tracey L SlettenTurner Institute for Brain and Mental Health, School of Psychological Sciences, Monash University, Building 2, 270 Ferntree Gully Road, Notting Hill, Victoria, 3168, AustraliaTel + 61 3 990 20734Email tracey.sletten@monash.eduPurpose: This study examined the efficacy of a lighting intervention that increased both light intensity and short-wavelength (blue) light content to improve alertness, performance and mood in night shift workers in a chemical plant.Patients and Methods: During rostered night shifts, 28 workers (46.0± 10.8 years; 27 male) were exposed to two light conditions each for two consecutive nights (∼ 19:00– 07:00 h) in a counterbalanced repeated measures design: traditional-spectrum lighting set at pre-study levels (43 lux, 4000 K) versus higher intensity, blue-enriched lighting (106 lux, 17,000 K), equating to a 4.5-fold increase in melanopic illuminance (24 to 108 melanopic illuminance). Participants completed the Karolinska Sleepiness Scale, subjective mood ratings, and the Psychomotor Vigilance Task (PVT) every 2– 4 hours during the night shift.Results: A significant main effect of time indicated KSS, PVT mean reaction time, number of PVT lapses (reaction times > 500 ms) and subjective tension, misery and depression worsened over the course of the night shift (p< 0.05). Percentage changes in KSS (p< 0.05, partial η2=0.14) and PVT mean reaction time (p< 0.05, partial η2=0.19) and lapses (p< 0.05, partial η2=0.17) in the middle and end of night shift, expressed relative to start of shift, were significantly improved during the lighting intervention compared to the traditional lighting condition. Self-reported mood did not significantly differ between conditions (p> 0.05).Conclusion: Our findings, showing improvements in alertness and performance with exposure to blue-enriched, increased intensity light, provide support for light to be used as a countermeasure for impaired alertness in night shift work settings.Keywords: shift work, circadian photoreception, alertness, vigilance, light, short-wavelength

Internal circadian phase assessment is increasingly acknowledged as a critical clinical tool for the diagnosis, monitoring, and treatment of circadian rhythm sleep-wake disorders and for investigating circadian timing in other medical disorders. The widespread use of in-laboratory circadian phase assessments in routine practice has been limited, most likely because circadian phase assessment is not required by formal diagnostic nosologies, and is not generally covered by insurance. At-home assessment of salivary dim light melatonin onset (DLMO, a validated circadian phase marker) is an increasingly accepted approach to assess circadian phase. This approach may help meet the increased demand for assessments and has the advantages of lower cost and greater patient convenience. We reviewed the literature describing at-home salivary DLMO assessment methods and identified factors deemed to be important to successful implementation. Here, we provide specific protocol recommendations for conducting at-home salivary DLMO assessments to facilitate a standardized approach for clinical and research purposes. Key factors include control of lighting, sampling rate, and timing, and measures of patient compliance. We include findings from implementation of an optimization algorithm to determine the most efficient number and timing of samples in patients with Delayed Sleep-Wake Phase Disorder. We also provide recommendations for assay methods and interpretation. Providing definitive criteria for each factor, along with detailed instructions for protocol implementation, will enable more widespread adoption of at-home circadian phase assessments as a standardized clinical diagnostic, monitoring, and treatment tool., (© 2024 The Author(s). Journal of Pineal Research published by John Wiley & Sons Ltd.)

Robust circadian rhythms are essential for optimal health. The central circadian clock controls temperature rhythms, which are known to organize the timing of peripheral circadian rhythms in rodents. In humans, however, it is unknown whether temperature rhythms relate to the organization of circadian rhythms throughout the body. We assessed core body temperature amplitude and the rhythmicity of 929 blood plasma metabolites across a 40-h constant routine protocol, controlling for behavioral and environmental factors that mask endogenous temperature rhythms, in 23 healthy individuals (mean [± SD] age = 25.4 ± 5.7 years, 5 women). Valid core body temperature data were available in 17/23 (mean [± SD] age = 25.6 ± 6.3 years, 1 woman). Individuals with higher core body temperature amplitude had a greater number of metabolites exhibiting circadian rhythms (R 2  = 0.37, p = .009). Higher core body temperature amplitude was also associated with less variability in the free-fitted periods of metabolite rhythms within an individual (R 2  = 0.47, p = .002). These findings indicate that a more robust central circadian clock is associated with greater organization of circadian metabolite rhythms in humans. Metabolite rhythms may therefore provide a window into the strength of the central circadian clock., (© 2024. The Author(s).)

Study Objectives: We previously reported that during a 45-day simulated space mission, a dynamic lighting schedule (DLS) improved circadian phase alignment and performance assessed once on selected days. This study aimed to evaluate how DLS affected performance on a 5-minute psychomotor vigilance task (PVT) administered multiple times per day on selected days., Methods: Sixteen crewmembers (37.4 ± 6.7 years; 5F) underwent six cycles of 2 × 8-hour/night followed by 5 × 5-hour/night sleep opportunities. During the DLS ( n  = 8), daytime white light exposure was blue-enriched (~6000 K; Level 1: 1079, Level 2: 76 melanopic equivalent daytime illuminance (melEDI) lux) and blue-depleted (~3000-4000 K; L1: 21, L2: 2 melEDI lux) 3 hours before bed. In the standard lighting schedule (SLS; n  = 8), lighting remained constant (~4500K; L1: 284, L2 62 melEDI lux). Effects of lighting condition (DLS/SLS), sleep condition (5/8 hours), time into mission, and their interactions, and time awake on PVT performance were analyzed using generalized linear mixed models., Results: The DLS was associated with fewer attentional lapses (reaction time [RT] > 500 milliseconds) compared to SLS. Lapses, mean RT, and 10% fastest/slowest RTs were worse following 5 compared to 8 hours of sleep but not between lighting conditions. There was an effect of time into mission on RTs, likely due to sleep loss. Overall performance differed by time of day, with longer RTs at the beginning and end of the day. There were more lapses and slower RTs in the afternoon in the SLS compared to the DLS condition., Conclusions: Future missions should incorporate DLS to enhance circadian alignment and performance. This paper is part of the Sleep and Circadian Rhythms: Management of Fatigue in Occupational Settings Collection., (© The Author(s) 2024. Published by Oxford University Press on behalf of Sleep Research Society.)

Sleep deprivation enhances risk for serious injury and fatality on the roads and in workplaces. To facilitate future management of these risks through advanced detection, we developed and validated a metabolomic biomarker of sleep deprivation in healthy, young participants, across three experiments. Bi-hourly plasma samples from 2 × 40-hour extended wake protocols (for train/test models) and 1 × 40-hour protocol with an 8-hour overnight sleep interval were analyzed by untargeted liquid chromatography-mass spectrometry. Using a knowledge-based machine learning approach, five consistently important variables were used to build predictive models. Sleep deprivation (24 to 38 hours awake) was predicted accurately in classification models [versus well-rested (0 to 16 hours)] (accuracy = 94.7%/AUC 99.2%, 79.3%/AUC 89.1%) and to a lesser extent in regression ( R 2 = 86.1 and 47.8%) models for within- and between-participant models, respectively. Metabolites were identified for replicability/future deployment. This approach for detecting acute sleep deprivation offers potential to reduce accidents through "fitness for duty" or "post-accident analysis" assessments.

Women typically sleep and wake earlier than men and have been shown to have earlier circadian timing relative to the light/dark cycle that synchronizes the clock. A potential mechanism for earlier timing in women is an altered response of the circadian system to evening light. We characterized individual-level dose-response curves for light-induced melatonin suppression using a within-subjects protocol. Fifty-six participants (29 women, 27 men; aged 18-30 years) were exposed to a range of light illuminances (10, 30, 50, 100, 200, 400, and 2000 lux) using melatonin suppression relative to a dim control (<1 lux) as a marker of light sensitivity. Women were free from hormonal contraception. To examine the potential influence of sex hormones, estradiol and progesterone was examined in women and testosterone was examined in a subset of men. Menstrual phase was monitored using self-reports and estradiol and progesterone levels. Women exhibited significantly greater melatonin suppression than men under the 400-lux and 2000-lux conditions, but not under lower light conditions (10-200 lux). Light sensitivity did not differ by menstrual phase, nor was it associated with levels of estradiol, progesterone, or testosterone, suggesting the sex differences in light sensitivity were not acutely driven by circulating levels of sex hormones. These results suggest that sex differences in circadian timing are not due to differences in the response to dim/moderate light exposures typically experienced in the evening. The finding of increased bright light sensitivity in women suggests that sex differences in circadian timing could plausibly instead be driven by a greater sensitivity to phase-advancing effects of bright morning light., (© 2024 The Authors. Journal of Pineal Research published by John Wiley & Sons Ltd.)

Objective: To investigate the influence of the degree of circadian adaptation to night work on sleep architecture following night shift., Methods: Thirty four night workers (11 females; 33.8 ± 10.1years) completed a simulated night shift following 2-7 typical night shifts. Participants completed a laboratory-based simulated night shift (21:00-07:00 hours), followed by a recovery sleep opportunity (∼09:00-17:00 hours), recorded using polysomnography. Urinary 6-sulphatoxymelatonin (aMT6s) rhythm acrophase was used as a marker of circadian phase. Sleep duration and architecture were compared between individuals with aMT6s acrophase before (unadapted group, n = 22) or after (partially adapted group, n = 12) bedtime., Results: Bedtime occurred on average 2.16 hours before aMT6s acrophase in the partially adapted group and 3.91 hours after acrophase in the unadapted group. The partially adapted group had more sleep during the week before the simulated night than the unadapted group (6.47 ± 1.02 vs. 5.26 ± 1.48 hours, p = .02). After the simulated night shift, both groups had similar total sleep time (partially adapted: 6.68 ± 0.80 hours, unadapted: 6.63 ± 0.88 hours, p > .05). The partially adapted group had longer total rapid eye movement sleep duration than the unadapted group (106.79 ± 32.05 minutes vs. 77.90 ± 28.86 minutes, p = .01). After 5-hours, rapid eye movement sleep accumulation was higher in the partially adapted compared to the unadapted group (p = .02). Sleep latency and other stages were not affected by circadian adaptation., Discussion: Partial circadian adaptation to night shift was associated with longer rapid eye movement sleep duration during daytime sleep, highlighting the influence of entrainment between the sleep-wake cycle and the circadian pacemaker in night workers. The findings have important implications for sleep and subsequent alertness associated with shift work., Competing Interests: Declaration of conflicts of interest Iona Zimberg, Suzanne Ftouni and Michelle Magee have no conflicts of interest to disclose. Sally Ferguson reports that through her institution she has received research grants from SafeWorkSA, Sleep Health Foundation; Australian Research Council, Australian Government Department of Industry, Innovation and Science; Defence, Science and Technology Organisation, Australian Maritime Safety Authority and Queensland Health. Steven Lockley has no conflicts of interests related to the research or results reported in this paper. In the interests of full disclosure, commercial interests are listed below. SWL has received consulting fees from the Atlanta Falcons, Atlanta Hawks, BHP Billiton, Noble Insights, Slingshot Insights and Team C Racing; honoraria and/or paid travel from BHP Billiton, DIN, Emory University, IES, Ineos, SLTBR, Solemma and Teague; has current consulting contracts with Akili Interactive, Apex2100 Ltd, Consumer Sleep Solutions, Headwaters Inc, Hintsa PERformance AG, LightCognitive, Lighting Science Group Corporation, Mental Workout, PlanLED, Six Senses, Stantec and Wyle Integrated Science and Engineering; has received unrestricted equipment gifts from Bionetics Corporation and F. Lux Software LLC and royalties from Oxford University Press; and has served as a paid expert in legal proceedings related to light, sleep and health. He holds a patent through Harvard University and Brigham and Women's Hospital for “Systems and Methods for Determining and/or Controlling Sleep Quality.” Shantha Rajaratnam reports unpaid appointments at the Cooperative Research Centre for Alertness, Safety and Productivity, Australia and the Sleep Health Foundation. Dr. Rajaratnam is supported on grants from Vanda Pharmaceuticals, Philips Respironics, Cephalon, Rio Tinto, BHP Billiton and Shell. Dr. Rajaratnam has received other support from Optalert, Compumedics, Teva Pharmaceuticals and Circadian Therapeutics, through his institution. He is a member of the National Sleep Foundation Sleep Timing Variability Consensus Panel, for which he was paid an honorarium through his institution. Tracey Sletten reports her institution has received equipment donations or other support from Philips Lighting, Philips Respironics, Optalert and Compumedics. Dr. Sletten was a Project Leader and received grants for research from the Cooperative Research Centre for Alertness, Safety and Productivity. Dr. Sletten has received consulting fees from Vanda Pharmaceuticals and is a member of the National Sleep Foundation Sleep Timing Variability Consensus Panel, for which she was paid an honorarium., (Copyright © 2024 National Sleep Foundation. Published by Elsevier Inc. All rights reserved.)

Objectives: Mathematical models of human neurobehavioral performance that include the effects of acute and chronic sleep restriction can be key tools in assessment and comparison of work schedules, allowing quantitative predictions of performance when empirical assessment is impractical., Methods: Using such a model, we tested the hypothesis that resident physicians working an extended duration work roster, including 24-28 hours of continuous duty and up to 88 hours per week averaged over 4weeks, would have worse predicted performance than resident physicians working a rapidly cycling work roster intervention designed to reduce the duration of extended shifts. The performance metric used was attentional failures (ie, Psychomotor Vigilance Task lapses). Model input was 169 actual work and sleep schedules. Outcomes were predicted hours per week during work hours spent at moderate (equivalent to 16-20 hours of continuous wakefulness) or high (equivalent to ≥20 hours of continuous wakefulness) performance impairment., Results: The model predicted that resident physicians working an extended duration work roster would spend significantly more time at moderate impairment (p = .02, effect size=0.2) than those working a rapidly cycling work roster; this difference was most pronounced during the circadian night (p < .001). On both schedules, performance was predicted to decline from weeks 1 + 2 to weeks 3 + 4 (p < .001), but the rate of decline was significantly greater on extended duration work roster (p < .01). Predicted performance impairment was inversely related to prior sleep duration (p < .001)., Conclusions: These findings demonstrate the utility of a mathematical model to evaluate the predicted performance profile of schedules for resident physicians and others who experience chronic sleep restriction and circadian misalignment., Competing Interests: Declaration of conflict of interest Dr. Phillips has received research funding from Versalux and Delos, and he is co-founder and co-director of Circadian Health Innovations PTY LTD. He also holds a patent (US20150080756A1) for estimating arousal states from ambulatory recordings by using sleep and wake models. Dr. St Hilaire has received grant/research support from NIH, NASA, and Merrimack College. Dr. Barger reports honorariums from AAA Foundation, University of Arizona and University of British Columbia. Mr. O’Brien has no COI to report from the past 3 years. Dr. Rahman holds patents for (1) Method and device for preventing alterations in circadian rhythm (U.S. patent application Ser. No. 10/525,958), and (2) Methods and devices for improving sleep performance in subject exposed to light at night (U.S. Application No. 61/810,985); owns equity in Melcort Inc; has provided paid consulting services to Sultan & Knight Limited, Bambu Vault LLC, Lucidity Lighting Inc; and has received honoraria as an invited speaker and travel funds from Starry Skies Lake Superior, University of Minnesota Medical School, PennWell Corp, and Seoul Semiconductor Co Ltd, FALK FOUNDATION E.V.; and has received grant/research support from Seoul Semiconductor Co Ltd, Biological Innovation and Optimization Systems, LLC, Merck & Co, Inc, Pfizer Inc, Vanda Pharmaceuticals Inc, Lighting Science Group, NIH, and NASA. These interests were reviewed and managed by Brigham and Women's Hospital and Mass General Brigham in accordance with their conflict-of-interest policies. Dr. Landrigan holds equity in and has consulted with the I-PASS Patient Safety Institute, which seeks to train institutions in best handoff practices and aid in their implementation. In addition, Dr. Landrigan has received monetary awards, honoraria, and travel reimbursement from multiple academic and professional organizations for teaching and consulting on sleep deprivation, physician performance, handoffs, and safety, and has served as an expert witness in cases regarding patient safety and sleep deprivation. Dr. Lockley reports consulting fees from the Hintsa Performance AG, Stantec and View Inc, and has consulting contracts with Absolute Rest, Akili Interactive, Apex 2100 Ltd, Ashurst Risk Advisory, Consumer Sleep Solutions, KBR Wyle Services, Light Cognitive; Lighting Science Group Corporation/HealthE; and Mental Workout/Timeshifter. He has received honoraria and travel or accommodation expenses from Bloxhub, Clifton College, Danish Centre for Lighting, and University of Toronto; and travel or accommodation expenses (no honoraria) from Wiley; and royalties from Monash University and Oxford University Press. He holds equity in iSleep pty. He has received an unrestricted equipment gift and investigator-initiated grant from F. Lux Software LLC, and a Clinical Research Support Agreement and Clinical Trial Agreement with Vanda Pharmaceuticals Inc. He is an unpaid Board Member of the Midwest Lighting Institute (non-profit). He was a Program Leader for the CRC for Alertness, Safety and Productivity, Australia, through an adjunct professor position at Monash University (2015-2019). He is part-time adjunct professor at the University of Surrey, UK. He holds several pending patents (US2019366032A1; USD943612S1; US2021162164A1, US20220151552A1). He has served as a paid expert in legal proceedings related to light, sleep, and health. His interests are reviewed and managed by Mass General Brigham in accordance with their conflict-of-interest policies. Dr. Czeisler reports that he serves as the incumbent of an endowed professorship provided to Harvard Medical School by Cephalon, Inc and reports institutional support for a Quality Improvement Initiative from Delta Airlines and Puget Sound Pilots; education support to Harvard Medical School Division of Sleep Medicine and support to Brigham and Women’s Hospital from: Jazz Pharmaceuticals PLC, Inc, Philips Respironics, Inc, Optum, and ResMed, Inc; research support to Brigham and Women’s Hospital from Axsome Therapeutics, Inc, Dayzz Ltd, Peter Brown and Margaret Hamburg, Regeneron Pharmaceuticals, Sanofi SA, Casey Feldman Foundation, Summus, Inc, Takeda Pharmaceutical Co, LTD, Abbaszadeh Foundation, CDC Foundation; educational funding to the Sleep and Health Education Program of the Harvard Medical School Division of Sleep Medicine from ResMed, Inc, Teva Pharmaceuticals Industries, Ltd, and Vanda Pharmaceuticals; personal royalty payments on sales of the Actiwatch-2 and Actiwatch-Spectrum devices from Philips Respironics, Inc; personal consulting fees from Axsome Therapeutics, Bryte Foundation, With Deep, Inc and Vanda Pharmaceuticals; honoraria from the Associated Professional Sleep Societies, LLC for the Thomas Roth Lecture of Excellence at SLEEP 2022, from the Massachusetts Medical Society for a New England Journal of Medicine Perspective article, from the National Council for Mental Wellbeing, from the National Sleep Foundation for serving as chair of the Sleep Timing and Variability Consensus Panel, for lecture fees from Teva Pharma Australia PTY Ltd and Emory University, and for serving as an advisory board member for the Institute of Digital Media and Child Development, the Klarman Family Foundation, and the UK Biotechnology and Biological Sciences Research Council. CAC has received personal fees for serving as an expert witness on a number of civil matters, criminal matters, and arbitration cases, including those involving the following commercial and government entities: Amtrak; Bombardier, Inc; C&J Energy Services; Dallas Police Association; Delta Airlines/Comair; Enterprise Rent-A-Car; FedEx; Greyhound Lines, Inc/Motor Coach Industries/FirstGroup America; PAR Electrical Contractors, Inc; Puget Sound Pilots; the San Francisco Sheriff’s Department; Schlumberger Technology Corp; Union Pacific Railroad; United Parcel Service; and Vanda Pharmaceuticals. CAC has received travel support from Merck, Sharpe and Dohme for travel to Japan and Australia; equity interest in Vanda Pharmaceuticals, With Deep, Inc, WHOOP, Inc, and Signos, Inc; and institutional educational gifts to Brigham and Women’s Hospital from Johnson & Johnson, Mary Ann and Stanley Snider via Combined Jewish Philanthropies, Alexandra Drane, DR Capital, Harmony Biosciences, LLC, San Francisco Bar Pilots, Whoop, Inc, Harmony Biosciences LLC, Eisai Co, LTD, Idorsia Pharmaceuticals LTD, Sleep Number Corp, Apnimed, Inc, Avadel Pharmaceuticals, Bryte Foundation, f.lux Software, LLC, Stuart F. and Diana L. Quan Charitable Fund. Dr. Czeisler's interests were reviewed and are managed by the Brigham and Women's Hospital and Mass General Brigham in accordance with their conflict-of-interest policies. Dr. Klerman reports consulting for the American Academy of Sleep Medicine Foundation, Circadian Therapeutics, National Sleep Foundation, Puerto Rico Science, Technology, and Research Trust, Pfizer Pharmaceuticals, Sanofi-Genzyme, Sleep Research Society Foundation, and Yale University Press; travel support from the DGSM (Germany Sleep Society), EPFL Pavilions, European Biological Rhythms Society, Gordon Research Conference, Santa Fe Research Institute, Sleep Research Society, and World Conference of Chronobiology; and being on the Scientific Advisory Board (unpaid) for Chronsulting. Other: Partner is founder, director, and chief scientific officer of Chronsulting., (Copyright © 2024 National Sleep Foundation. Published by Elsevier Inc. All rights reserved.)

Objectives: For optimal health and well-being the sleep episode and the circadian timing system should be properly aligned. We evaluated the effectiveness of different dynamic light and sleep/wake shift schedules for rapid circadian entrainment following an 8-hour advance of sleep., Methods: Forty-three healthy participants completed an 8-day inpatient protocol in which the 8-hour sleep episode was advanced by 8 hours. Participants were assigned to one of five conditions: (1) dim ambient WHITE light and GRADUAL shift in which the sleep episode was incrementally advanced over 5days; (2) dim GREEN, short-wavelength (∼504 nm) polychromatic light and GRADUAL shift; (3) dim WHITE light and SLAM shift, including an abrupt 8-hour advance on day 3 following an extended 32-hour wake episode; (4) GREEN light and SLAM shift; or (5) COMBINED (higher illuminance WHITE plus GREEN) light and modified SLAM shift with 2 short naps scheduled on the day prior to the abrupt advance. Phase shifts of the plasma dim light melatonin onset and sleep measures were compared to examine effects of protocol condition., Results: After 5days, the COMBINED light/modified SLAM shift condition showed larger phase advances of dim light melatonin onset (4.02 ± 1.13 hours) compared to the other 4 conditions (range 1.50 ± 0.96-2.83 ± 2.23 hours; p < .05) and resulted in increased REM sleep duration and fewer sleep disruptions., Conclusions: Consideration of the type of shift and the illuminance and wavelength of light may assist in designing lighting countermeasures to sleep and circadian disruption, which has implications for jetlag, shiftwork, and circadian rhythm sleep disorders., Competing Interests: Declaration of conflicts of interest A-MC has no conflicts of interest to disclose for this work. Outside of the work presented here, A-MC has received a grant to the Pennsylvania State University from Kunasan, Inc., and honoraria/travel support for lectures from the University of Miami. CA has no conflicts of interest for this work, but in the interest of full disclosure: CA has received a research award/prize from Sanofi-Aventis; contract research support from VicRoads, Rio Tinto Coal Australia, National Transport Commission, Tontine/Pacific Brands, and AAA Foundation; industry funding through ARC Linkage scheme with Seeing Machines and Cogstate Ltd; and lecturing fees from Brown Medical School/Rhode Island Hospital, Ausmed, Healthmed and TEVA Pharmaceuticals; and reimbursements for conference travel expenses from Philips Healthcare. In addition, she has served as a consultant to the Rail, Bus and Tram Union, the Transport Accident Commission (TAC), the National Transportation Committee (NTC), VicRoads, and Melius Consulting. She has also served as an expert witness and/or consultant in relation to fatigue and drowsy driving, and was a Theme Leader in the Cooperative Research Centre for Alertness, Safety and Productivity. SWC has received research funds from Versalux and Delos, and consulted for Beacon Lighting, Versalux, and Dyson. DAR has no conflicts of interest to disclose. JMR has no conflicts of interest to disclose. SWL reports commercial interests from the last 3 years (2020-2023). His interests are reviewed and managed by Brigham and Women's Hospital and Partners HealthCare in accordance with their conflict-of-interest policies. SWL has received consulting fees from Hintsa Performance AG, Stantec and View Inc, and has consulting contracts with Absolute Rest, Akili Interactive, Apex 2100 Ltd, Ashurst Risk Advisory, Consumer Sleep Solutions, KBR Wyle Services, Light Cognitive; Lighting Science Group Corporation/HealthE; Mental Workout/Timeshifter. He has received honoraria and travel or accommodation expenses from Bloxhub, Clifton College, Danish Centre for Lighting, and University of Toronto; and travel or accommodation expenses (no honoraria) from Wiley; and royalties from Oxford University Press and Monash University. He holds equity in iSleep pty. He has received an unrestricted equipment gift and investigator-initiated grant from F. Lux Software LLC, and a Clinical Research Support Agreement and Clinical Trial Agreement with Vanda Pharmaceuticals Inc. He is an unpaid Board Member of the Midwest Lighting Institute (non-profit). He is part-time adjunct professor at the University of Surrey, UK. He holds several pending (US20190366032; US20210162164 US20220151552) and one awarded (USD943612) patents. He has served as a paid expert in legal proceedings related to light, sleep and health. CAC serves as the incumbent of an endowed professorship provided to Harvard Medical School by Cephalon, Inc. and reports institutional support for a Quality Improvement Initiative from Delta Airlines and Puget Sound Pilots; education support to Harvard Medical School Division of Sleep Medicine and support to Brigham and Women’s Hospital from: Jazz Pharmaceuticals PLC, Inc, Philips Respironics, Inc., Optum, and ResMed, Inc.; research support to Brigham and Women’s Hospital from Axome Therapeutics, Inc., Dayzz Ltd., Peter Brown and Margaret Hamburg, Regeneron Pharmaceuticals, Sanofi SA, Casey Feldman Foundation, Summus, Inc., Takeda Pharmaceutical Co., LTD, Abbaszadeh Foundation, CDC Foundation; educational funding to the Sleep and Health Education Program of the Harvard Medical School Division of Sleep Medicine from ResMed, Inc., Teva Pharmaceuticals Industries, Ltd., and Vanda Pharmaceuticals; personal royalty payments on sales of the Actiwatch-2 and Actiwatch-Spectrum devices from Philips Respironics, Inc; personal consulting fees from Axsome, Inc., Bryte Foundation, With Deep, Inc. and Vanda Pharmaceuticals; honoraria from the Associated Professional Sleep Societies, LLC for the Thomas Roth Lecture of Excellence at SLEEP 2022, from the Massachusetts Medical Society for a New England Journal of Medicine Perspective article, from the National Council for Mental Wellbeing, from the National Sleep Foundation for serving as chair of the Sleep Timing and Variability Consensus Panel, for lecture fees from Teva Pharma Australia PTY Ltd. and Emory University, and for serving as an advisory board member for the Institute of Digital Media and Child Development, the Klarman Family Foundation, and the UK Biotechnology and Biological Sciences Research Council. Dr. Czeisler has received personal fees for serving as an expert witness on a number of civil matters, criminal matters, and arbitration cases, including those involving the following commercial and government entities: Amtrak; Bombardier, Inc.; C&J Energy Services; Dallas Police Association; Delta Airlines/Comair; Enterprise Rent-A-Car; FedEx; Greyhound Lines, Inc./Motor Coach Industries/FirstGroup America; PAR Electrical Contractors, Inc.; Puget Sound Pilots; and the San Francisco Sheriff’s Department; Schlumberger Technology Corp.; Union Pacific Railroad; United Parcel Service; and Vanda Pharmaceuticals. Dr. Czeisler has received travel support from the Stanley Ho Medical Development Foundation for travel to Macao and Hong Kong; equity interest in Vanda Pharmaceuticals, With Deep, Inc, and Signos, Inc.; and institutional educational gifts to Brigham and Women’s Hospital from Johnson & Johnson, Mary Ann and Stanley Snider via Combined Jewish Philanthropies, Alexandra Drane, DR Capital, Harmony Biosciences, LLC, San Francisco Bar Pilots, Whoop, Inc., Harmony Biosciences LLC, Eisai Co., LTD, Idorsia Pharmaceuticals LTD, Sleep Number Corp., Apnimed, Inc., Avadel Pharmaceuticals, Bryte Foundation, f.lux Software, LLC, and the Stuart F. and Diana L. Quan Charitable Fund. Dr Czeisler's interests were reviewed and are managed by the Brigham and Women's Hospital and Mass General Brigham in accordance with their conflict-of interest policies., (Copyright © 2024. Published by Elsevier Inc.)

Objective: To examine effects of menstrual phase and nighttime light exposure on subjective sleepiness and auditory Psychomotor Vigilance Task performance., Methods: Twenty-nine premenopausal women (12 =Follicular; 17 =Luteal) completed a 6.5-hour nighttime monochromatic light exposure with varying wavelengths (420-620 nm) and irradiances (1.03-14.12 µW/cm 2 ). Subjective sleepiness, reaction time, and attentional lapses were compared between menstrual phases in women with minimal (<33%) or substantial (≥33%) light-induced melatonin suppression., Results: When melatonin was not suppressed, women in the follicular phase had significantly worse reaction time (mean difference=145.1 ms, 95% CI 51.8-238.3, p < .001, Cohen's D=1.9) and lapses (mean difference=12.9 lapses, 95% CI 4.37-21.41, p < .001, Cohen's D=1.7) compared to women in the luteal phase. When melatonin was suppressed, women in the follicular phase had significantly better reaction time (mean difference=152.1 ms, 95% CI 43.88-260.3, p < .001, Cohen's D=1.7) and lapses (mean difference=12.3 lapses, 95% CI 1.14-25.6, p < .01, Cohen's D=1.6) compared to when melatonin was not suppressed, such that their performance was not different (p > .9) from women in the luteal phase. Subjective sleepiness did not differ by menstrual phase (mean difference=0.6, p > .08) or melatonin suppression (mean difference=0.2, p > .4)., Conclusions: Nighttime light exposure sufficient to suppress melatonin can also mitigate neurobehavioral performance deficits associated with the follicular phase. Despite the relatively small sample size, these data suggest that nighttime light may be a valuable strategy to help reduce errors and accidents in female shift workers., (Copyright © 2024 National Sleep Foundation. Published by Elsevier Inc. All rights reserved.)

Human cognitive impairment associated with sleep loss, circadian misalignment and work overload is a major concern in any high stress occupation but has potentially catastrophic consequences during spaceflight human robotic interactions. Two safe, wake-promoting countermeasures, caffeine and blue-enriched white light have been studied on Earth and are available on the International Space Station. We therefore conducted a randomized, placebo-controlled, cross-over trial examining the impact of regularly timed low-dose caffeine (0.3 mg per kg per h) and moderate illuminance blue-enriched white light (~90 lux, ~88 melEDI lux, 6300 K) as countermeasures, separately and combined, in a multi-night simulation of sleep-wake shifts experienced during spaceflight among 16 participants (7 F, ages 26-55). We find that chronic administration of low-dose caffeine improves subjective and objective correlates of alertness and performance during an overnight work schedule involving chronic sleep loss and circadian misalignment, although we also find that caffeine disrupts subsequent sleep. We further find that 90 lux of blue-enriched light moderately reduces electroencephalogram (EEG) power in the theta and delta regions, which are associated with sleepiness. These findings support the use of low-dose caffeine and potentially blue-enriched white light to enhance alertness and performance among astronauts and shiftworking populations., (© 2023. The Author(s).)