Charles Czeisler

Harvard Medical School | HMS · Division of Sleep Medicine

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...

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...

A potential contributor to insufficient sleep among college students is their daily schedule, with sleep sacrificed for other waking activities. We investigated how daily schedules predict day-to-day sleep-wake timing in college students. 223 undergraduate college students (M±SD = 19.2±1.4 years, 37% females) attending a Massachusetts university in...

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...

Background : Unpaid caregivers of adults play critical roles in health care systems by providing care to older adults and those with chronic conditions. The COVID-19 pandemic has heightened caregiving needs, forcing some into caregiving roles and disrupting others. We sought to estimate the prevalence of and identify factors associated with adverse...

Adults with disabilities, a group including >25% of U.S. adults (1), experience higher levels of mental health and substance use conditions and lower treatment rates than do adults without disabilities* (2,3). Survey data collected during April-September 2020 revealed elevated adverse mental health symptoms among adults with disabilities (4) compar...

Objective: To evaluate whether caregiving for older adults is associated with insomnia symptoms and diminished workplace productivity. Methods: We analyzed data collected from caregivers to older adults in the US. Participants self-reported awakenings from sleep (caregiving-related or spontaneous) and workplace measures (presenteeism, absenteeis...

Study objectives: To determine whether there was evidence of circadian or sleep-regulatory dysfunction in sighted individuals with Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD). Methods: Three sighted individuals with signs and/or symptoms of N24SWD were studied. Thirty-five to three-hundred and thirty-two day laboratory and home-based assessm...

Two patients with delayed sleep-wake phase disorder (DSWPD) demonstrated improvement in sleep quality and duration, reduction in symptoms, and elimination of the need for hypnotic or stimulant medications after changing their sleep schedules in response to the coronavirus disease 2019 (COVID-19) pandemic lockdown work schedule changes. These cases...

Rigorous nonpharmaceutical interventions (e.g., stay-at-home orders, remote-work directives) were implemented in early 2020 for coronavirus disease 2019 (COVID-19) pandemic containment in the U.S. During this time, increased sleep duration and delayed sleep timing were reported through surveys (Leone et al., 2021) and wearable data (Rezaei and Gran...

Objectives: Due to the significant mortality and morbidity consequences of the coronavirus 2019 (COVID-19) pandemic among older adults, these individuals were urged to avoid going out in public and socializing with others, among other major disruptions to daily life. While these significant and often unavoidable disruptions have been shown to bear...

Early during the COVID-19 pandemic, nearly two thirds of unpaid caregivers of adults reported adverse mental or behavioral health symptoms, compared with approximately one third of noncaregivers† (1). In addition, 27% of parents of children aged <18 years reported that their mental health had worsened during the pandemic (2). To examine mental heal...

Sleep difficulties have been implicated in the development and progression of dementia and in all-cause mortality. This study examines the relationship between sleep difficulties, incident dementia and all-cause mortality over 8 years of follow-up among a nationally representative sample of older (≥65 years) adults in the United States. We used dat...

The COVID-19 pandemic has been associated with mental health consequences due to direct (i.e., SARS-CoV-2 infection, potentially due to neuronal or astrocytic infection, microvascular, or inflammatory mechanisms) and indirect (i.e., social and economic impacts of COVID-19 prevention measures) mechanisms. Investigation of mental health in a region w...

Shiftwork and circadian disruption are associated with adverse metabolic effects. Therefore, we examined whether clinical biomarkers of metabolic health are under endogenous circadian regulation using a 40‐h constant routine protocol (CR; constant environmental and behavioral conditions) and evaluated the impact of typical daily conditions with per...

The time of dim light melatonin onset (DLMO) is the gold standard for circadian phase assessment in humans, but collection of samples for DLMO is time and resource intensive. Numerous studies have attempted to estimate circadian phase from actigraphy data, but most of these studies have involved individuals on controlled and stable sleep-wake sched...

Aims Markedly elevated adverse mental health symptoms were widely observed early in the coronavirus disease-2019 (COVID-19) pandemic. Unlike the U.S., where cross-sectional data indicate anxiety and depression symptoms have remained elevated, such symptoms reportedly declined in the U.K., according to analysis of repeated measures from a large-scal...

Importance SARS-CoV-2 containment is estimated to require attainment of high (>80%) post-infection and post-vaccination population immunity. Objective To assess COVID-19 vaccine intentions among US adults and their children, and reasons for vaccine hesitancy among potential refusers. Design Internet-based surveys were administered cross-sectionally...

Introduction Melatonin levels are partially driven by the parenchyma volume of the pineal gland. Low urinary levels of 6‐sulfatoxymelatonin have been associated with increased risk of advanced prostate cancer, but the relationship between pineal gland volume and composition and prostate cancer risk has not been examined. Materials and Methods We u...

Objectives: Rotating shift work is associated with adverse outcomes due to circadian misalignment, sleep curtailment, work-family conflicts, and other factors. We tested a bright light countermeasure to enhance circadian adaptation on a counterclockwise rotation schedule. Methods: Twenty-nine adults (aged 20-40 years; 15 women) participated in a...

Background Governments worldwide recommended unprecedented measures to contain the coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). As pressure mounted to scale back measures, understanding public priorities was critical. We assessed initial public adherence with and support for s...

Objectif Notre objectif était d’identifier les tendances en matière de durée du sommeil et de Jet-Lag social en utilisant les données d’une application mobile populaire en France et au Canada, “iSommeil”. Méthodes Nous avons examiné 8 207 nuits de iSommeil, une application de suivi du sommeil très répandue en France et au Canada. Dans cette analys...