Charles Czeisler

Harvard Medical School | HMS · Division of Sleep Medicine

Screen-based digital media devices potentially impact pediatric sleep health, which is fundamental to healthy development. Systematic reviews of the literature consistently show that screen use is associated with delayed bedtimes, shorter sleep duration, and reduced sleep quality. Studies also demonstrate that interactivity, content, and timing of...

This Viewpoint reports the findings of a 2024 independent scientific evaluation of fatigue risk in air traffic operations commissioned by the US Federal Aviation Administration.

Sleep tracking by consumers is becoming increasingly prevalent; yet, few studies have evaluated the accuracy of such devices. We sought to evaluate the accuracy of three devices (Oura Ring Gen3, Fitbit Sense 2, and Apple Watch Series 8) compared to the gold standard sleep assessment (polysomnography (PSG)). Thirty-five participants (aged 20–50 year...

Study objectives: Insomnia, poor sleep quality and extremes of sleep duration are associated with COVID-19 infection. This study assessed whether these factors are related to Post-Acute Sequelae of SARS-CoV-2 infection (PASC). Methods: Cross-sectional survey of a general population of 24,803 U.S. adults to determine the association of insomnia,...

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, mo...

Cross-sectional studies suggest that obstructive sleep apnea (OSA) is a potential risk factor for incident COVID-19 infection, but longitudinal studies are lacking. In this study, two surveys from a large general population cohort, the COVID-19 Outbreak Public Evaluation (COPE) Initiative, undertaken 147 +/- 58 days apart were analyzed to determine...

Adaptation of the circadian clock to the environment is essential for optimal health, well-being, and performance. Animal models demonstrate that a high-fat diet impairs circadian adaptation to advances of the light-dark cycle; it is unknown whether this occurs in humans. Utilizing a natural experiment that occurs when humans must advance their beh...

Objectives To develop and implement a pilot online data collection tool to help local health departments with their COVID-19 pandemic response efforts and inform health department actions. Design The COVID-19 Outbreak Public Evaluation (COPE) was an online survey and was distributed by participating sites to individuals who recently tested positiv...

Study Objectives: Insomnia, poor sleep quality and extremes of sleep duration are associated with COVID-19 infection. This study assessed whether these factors are related to Post-Acute Sequelae of SARS-CoV-2 infection (PASC). Methods: Cross-sectional survey of a general population of 24,803 U.S. adults to determine the association of insomnia, poo...

Previous research has revealed that daily variations in human neurobehavioral functions are driven in part by the endogenous circadian system. The objective of this study was to explore whether there exists a circadian influence on performance regarding a risky decision-making task and to determine whether the performance changes with sleep depriva...

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 sel...

Introduction Accurate biomarkers of insufficient sleep have been a central interest of sleep scientists. Given advancements in artificial intelligence, researchers have explored non-invasive digital biomarkers from human voices. In this study, we conducted a within-participant counterbalanced controlled trial of chronic sleep restriction (CSR) and...

Introduction Sleep tracking using consumer devices is increasingly prevalent in the population. Given this interest, it is essential that data produced by these monitors is reliable and accurate. In a single night study with the primary aim of validating the Oura Ring in comparison to polysomnography (PSG), participants wore Oura Rings on their rig...

Introduction Minoritized groups in the United States experience discrimination that impacts their physical and mental well-being. People with multiple minoritized identities, such as being a racial/ethnic minority or sexual minority, often experience worsened health outcomes due to the intersectional nature of discrimination. The insidious nature o...

Introduction Circadian rhythms, which control sleep-wake cycles and metabolism, are fundamental to human health. Our study aimed to understand how these rhythms affect proteins in the body throughout the day, and to develop a tool that predicts the body's internal clock phase based on protein expression. Methods Plasma samples from 17 healthy adul...

Objective This study assesses whether chronotype is related to COVID-19 infection and whether there is an interaction with shift work. Methods Cross-sectional survey of 19,821 U.S. adults Results COVID-19 infection occurred in 40% of participants, 32.6% morning and 17.2% evening chronotypes. After adjusting for demographic and socioeconomic facto...

Background: Obstructive sleep apnea (OSA) is associated with COVID-19 infection. Fewer investigations have assessed OSA as a possible risk for the development of Post-Acute Sequelae of SARS-CoV-2 infection (PASC). Research Question: In a general population, is OSA associated with increased odds of PASC-related symptoms and with an overall definitio...

Objectives: To explore how the blood plasma proteome fluctuates across the 24-hour day and identify a subset of proteins that show endogenous circadian rhythmicity. Methods: Plasma samples from 17 healthy adults were collected hourly under controlled conditions de- signed to unmask endogenous circadian rhythmicity; in a subset of 8 participants, we...

The amount of time available in a day is fixed, and consequently, sleep is often sacrificed for waking activities. For college students, daily activities, comprised of scheduled classes, work, study, social, and other extracurricular events, are major contributors to insufficient and poor-quality sleep. We investigated the impact of daily schedules...

Objective: To develop and present consensus findings of the National Sleep Foundation sleep timing and variability panel regarding the impact of sleep timing variability on health and performance. Methods: The National Sleep Foundation assembled a panel of sleep and circadian experts to evaluate the scientific evidence and conduct a formal conse...

Aging alters the amplitude and phase of centrally regulated circadian rhythms. Here we evaluate whether peripheral circadian rhythmicity in the plasma lipidome is altered by aging through retrospective lipidomics analysis on plasma samples collected in 24 healthy individuals (9 females; mean ± SD age: 40.9 ± 18.2 years) including 12 younger (4 fema...

Objective: This study assesses whether chronotype is related to COVID-19 infection and whether there is an interaction with shift work. Methods: Cross-sectional survey of 19,821 U.S. adults Results: COVID-19 infection occurred in 40% of participants, 32.6% morning and 17.2% evening chronotypes. After adjusting for demographic and socioeconomic fact...

Patients with chronic rhinosinusitis (CRS) report improved sleep quality after dupilumab, an anti IL4/13 therapy. Concurrent CRS and obstructive sleep apnea (OSA) cases are not rare, and CRS seemingly raises nasal resistance. Thus, we hypothesized that improved sleep quality by dupilumab therapy in CRS patients might be due to lowered nasal resista...

The main aim of this study was to explore how melatonin onset timing and phase angle to bedtime in healthy older adults are impacted by prior light exposure. A total of 13 healthy older (ages 56-74) individuals were studied on two successive evenings. Prior to the first evening, the participants were in self-selected lighting conditions for the fir...

Introduction Shift work is increasingly common in our 24/7 society and can cause sleep disturbances and excessive sleepiness. Roughly 10-43% of shift workers are diagnosed with shift work disorder (SWD), characterized by excessive sleepiness accompanied by reduced sleep duration and/or insomnia. While more individuals work early morning shifts (shi...

Introduction Transportation workers are at risk for obstructive sleep apnea (OSA), yet OSA is commonly undiagnosed in this population. In a two-phase study, we design and evaluate a tailored, mobile health (mHealth) intervention aimed at achieving OSA awareness, including changes in OSA beliefs, among operators of large highway maintenance vehicles...

Study objectives: To examine whether drivers are aware of sleepiness and associated symptoms, and how subjective reports predict driving impairment and physiological drowsiness. Methods: Sixteen shift workers (19-65y; 9 women) drove an instrumented vehicle for 2-hours on a closed-loop track after a night of sleep and a night of work. Subjective...

Objective To determine whether long weekly work hours and shifts of extended duration (≥24 hours) are associated with adverse patient and physician safety outcomes in more senior resident physicians (postgraduate year 2 and above; PGY2+). Design Nationwide, prospective cohort study. Setting United States, conducted over eight academic years (2002...

Background: Medical comorbidities increase the risk of severe acute COVID-19 illness. Although sleep problems are common after COVID-19 infection, it is unclear whether insomnia, poor sleep quality and extremely long or short sleep increase risk of developing COVID-19 infection or hospitalization. Methods: Cross-sectional survey of a diverse sam...

Objectives: Studies have found associations between occupational burnout symptoms and reduced engagement with healthy behaviours. We sought to characterise demographic, employment and sleep characteristics associated with occupational burnout symptoms, and to evaluate their relationships with adherence to COVID-19 prevention behaviours (mask usage...

Study objectives: Sleep deficiency can adversely affect the performance of resident physicians resulting in greater medical errors. However, the impact of sleep deficiency on surgical outcomes, particularly among attending surgeons is less clear. Methods: Sixty attending surgeons from academic and community departments of surgery or obstetrics a...

Importance: US public health guidance has increasingly shifted responsibility for actions to minimize ongoing impacts of COVID-19 onto individuals. During September to October 2022, the World Health Organization continued to characterize COVID-19 as a pandemic. Yet, public perceptions of the pandemic status of COVID-19 and its associations with COV...

Human circadian, neuroendocrine, and neurobehavioral responses to light are mediated primarily by melanopsin-containing intrinsically-photosensitive retinal ganglion cells (ipRGCs) but they also receive input from visual photoreceptors. Relative photoreceptor contributions are irradiance- and duration-dependent but results for long-duration light e...

During the early stages of the COVID-19 pandemic, use of preventive behaviors was associated with perceived risk for contracting SARS-CoV-2 infection (1,2). Over time, perceived risk has declined along with waning COVID-19-related media coverage (3,4). The extent to which communities continue to be aware of local COVID-19 transmission levels and ar...

Circadian clocks drive cyclic variations in many aspects of physiology, but some daily variations are evoked by periodic changes in the environment or sleep-wake state and associated behaviors, such as changes in posture, light levels, fasting or eating, rest or activity and social interactions; thus, it is often important to quantify the relative...

Background: Medical comorbidities increase the risk of severe COVID-19 infection. In some studies, obstructive sleep apnea (OSA) has been identified as a comorbid condition that is associated with an increased prevalence of COVID-19 infection and hospitalization, but few have investigated this association in a general population. Research Question:...

Objectives We evaluated an online Sleep Health and Wellness (SHAW) programme paired with dayzz, a personalised sleep training programme deployed via smartphone application (dayzz app) that promotes healthy sleep and treatment for sleep disorders, among employees at a large healthcare organisation. Design Open-label, randomised, parallel-group cont...

Objectives: This study assessed the associations between parent intent to have their child receive the COVID-19 vaccination, and demographic factors and various child activities, including attendance at in-person education or childcare. Methods: Persons undergoing COVID-19 testing residing in Minnesota and Los Angeles County, California with childr...

Spaceflight exposes crewmembers to circadian misalignment and sleep loss, which impair cognition and increase the risk of errors and accidents. We compared the effects of an experimental dynamic lighting schedule (DLS) with a standard static lighting schedule (SLS) on circadian phase, self‐reported sleep and cognition during a 45‐day simulated spac...

Background: Sleep deficiency can adversely affect the performance of resident physicians resulting in greater medical errors. However, the impact of sleep deficiency on surgical outcomes, particularly among attending surgeons is less clear. Methods: Sixty attending surgeons from academic and community departments of surgery or obstetrics and gyneco...

Objectives: This study assessed the associations between parent intent to have their child receive COVID-19 vaccination, and demographic factors and various child activities including attendance at in-person education or childcare. Methods: Persons undergoing COVID-19 testing residing in Minnesota and Los Angeles County, California with children ag...

Background Given a downward age shift in COVID-19-involved deaths observed during the COVID-19 pandemic, we sought to estimate years of life lost (YLL) associated with leading causes of US death during the first 20 months of the pandemic. Findings Despite 4796 fewer COVID-19 deaths in Jan-Oct 2021 than in Mar-Dec 2020, the number of YLL due to COV...

We conducted a retrospective observational study using remote wearable and mobile application data to evaluate whether US public holidays or Daylight Saving Time transitions were associated with significant changes in sleep behaviors, including sleep duration, sleep onset and offset, and the consistency of sleep timing, as well as changes in the po...

Restorative sleep is a commonly used term but a poorly defined construct. Few studies have assessed restorative sleep in nationally representative samples. We convened a panel of 7 expert physicians and researchers to evaluate and enhance available measures of restorative sleep. We then developed the revised Restorative Sleep Questionnaire (REST-Q)...

Introduction Sleep deficiency and undiagnosed or untreated sleep disorders are pervasive among employed adults, yet are often ignored in the context of workplace health promotion. Smartphone applications (apps) are a promising, scalable approach to improving sleep among employees. We evaluated an online sleep education program followed by access to...

Background: The Accreditation Council for Graduate Medical Education (ACGME) enacted a policy in 2011 that restricted first-year resident physicians in the USA to work no more than 16 consecutive hours. This was rescinded in 2017. Methods: We conducted a nationwide prospective cohort study of resident physicians for 5 academic years (2002-2007)...

Circadian adaptation to shifted sleep/wake schedules may be facilitated by optimizing the timing, intensity and spectral characteristics of light exposure, which is the principal time cue for mammalian circadian pacemaker, and possibly by strategically timing non‐photic time cues such as exercise. Therefore, circadian phase resetting by light and e...

Aging is associated with changes in sleep, and improving sleep may have important consequences for the health, cognition, and quality of life of older adults. Many prescription sleep aids increase the risk of nighttime falls, have adverse effects on next‐day cognition, and are associated with increased mortality. Melatonin, a hormone secreted at ni...

Objectives To characterize objective sleep patterns among U.S. adults before and during the COVID-19 pandemic, and to assess for associations between adverse mental health symptoms and (1) sleep duration and (2) the consistency of sleep timing before and during the pandemic. Design Longitudinal objective sleep-wake data during January-June 2020 we...

Ocular light exposure has important influences on human health and well-being through modulation of circadian rhythms and sleep, as well as neuroendocrine and cognitive functions. Prevailing patterns of light exposure do not optimally engage these actions for many individuals, but advances in our understanding of the underpinning mechanisms and eme...

Chronic sleep restriction (CSR) has been associated with adverse effects including cognitive impairment and increased risk of diabetes and cardiovascular disease. Yet, sleep restriction therapy is an essential component of most behavioral treatments for insomnia. Moreover, little is known about the impact of CSR on sleep continuity and structure in...

Background: Nearly 14% of Americans experience chronic circadian disruption due to shift work, increasing their risk of obesity, diabetes, and other cardiometabolic disorders. These disorders are also exacerbated by modern eating habits such as frequent snacking and consumption of high-fat foods. Methods: We investigated the effects of recurrent...

While studies suggest that light and feeding patterns can reset circadian rhythms in various metabolites, whether these shifts follow a predictable pattern is unknown. We describe the first phase response curves (PRC) for lipids and hepatic proteins in response to combined light and food stimuli. The timing of plasma rhythms was assessed by constan...

The daily rhythm of plasma melatonin concentrations is typically unimodal, with one broad peak during the circadian night and near‐undetectable levels during the circadian day. Light at night acutely suppresses melatonin secretion and phase shifts its endogenous circadian rhythm. In contrast, exposure to darkness during the circadian day has not ge...

Sleep deficiency is a hidden cost of our 24–7 society, with 70% of adults in the US admitting that they routinely obtain insufficient sleep. Further, it is estimated that 50–70 million adults in the US have a sleep disorder. Undiagnosed and untreated sleep disorders are associated with diminished health for the individual and increased costs for th...

Sleep, a modifiable health behavior and an essential physiologic state, is a fundamental human need for overall health and survival. Sleep health has emerged as a broad concept to refer to healthy sleep. Sleep health involves several measurable dimensions including satisfaction, alertness, timing, efficiency, and duration. Sleep disorders and sleep...

Many people are concerned about whether they are getting “enough” sleep, and if they can “sleep too much.” These concerns can be approached scientifically using experiments probing long-term (i.e., multi-night) sleep homeostatic processes, since homeostatic processes move the system toward its physiological setpoint (i.e., between “not enough” and...

Diabetes affects approximately one in 10 persons in the United States† and is a risk factor for severe COVID-19 (1), especially when a patient's diabetes is not well managed (2). The extent to which the COVID-19 pandemic has affected diabetes care and management, and whether this varies across age groups, is currently unknown. To evaluate access to...

Sleep deficiencies and associated performance decrements are common among astronauts during spaceflight missions. Previously, sleep in space was analyzed with a focus on global measures while the intricate structure of sleep oscillations remains largely unexplored. This study extends previous findings by analyzing how spaceflight affects characteri...

We conducted a retrospective observational study using remote wearable and mobile application data to identify US public holidays associated with significant changes in sleep behaviors, including sleep duration, bedtime and waketime, and the consistency of sleep timing, as well as changes in the point prevalence of alcohol use. These metrics were c...

Study Objectives Clinical and population health recommendations are derived from studies that include self-report. Differences in question wording and response scales may significantly affect responses. We conducted a methodological review assessing variation in event definition(s), context (i.e., work- versus free-day), and timeframe (e.g., “in th...

Insufficient sleep, which has been shown to adversely affect metabolism, is generally associated with prolonged exposure to artificial light at night, a known circadian disruptor. There is growing evidence suggesting that circadian disruption adversely affects metabolism, yet few studies have attempted to evaluate the adverse metabolic effects of i...

Sleep deficiency and undiagnosed or untreated sleep disorders are pervasive among employed adults, yet often ignored in the context of workplace health promotion programs among employers. Smartphone applications (app) are a promising, scalable approach to improving sleep among employees. In this randomized clinical trial, we evaluate the dayzz app,...

Sleep deficiency is a hidden cost of our 24-7 society, with 70% of adults in the US admitting that they routinely obtain insufficient sleep. Further, it is estimated that 50-70 million adults in the US have a sleep disorder. Undiagnosed and untreated sleep disorders are associated with diminished health for the individual and increased costs for th...