To what extent is circadian phase predictive of subjective jet lag in long-haul cabin crew pre- and post-trip?

Long-haul cabin crew regularly report misalignment between their circadian phase and the external world (i.e. jet lag). The extent to which changes in circadian phase relate to reported levels of jet lag remains unclear. The main aim of the present study was first to evaluate the relationship between objective (circadian phase) and subjective jet lag and second to explore the relative role of both subjective and objective psycho-behavioural factors in predicting the subjective experience of jet lag. Twenty-eight long-haul cabin crew completed questionnaires measuring diurnal preference, trip characteristics and subjective jet lag as a single and as a multidimensional measure. Sleep was monitored using actigraphy and urinary melatonin peak time was measured, at baseline (T1), e.g. before a long-haul trip and post-trip on the crew's first recovery day (T2). Subjective jet lag was also measured at both time points. At T1, later circadian phase related to increased unidimensional jet lag, however, a post-trip discrepancy was found between objective and subjective uni- and multidimensional jet lag measured at T2 and change from T1 to T2. After controlling for direction and size of circadian phase, increased uni- and multidimensional subjective jet lag was predicted by depressed mood states. The regression models including phase, diurnal preference, departure time on the outbound sector and arousal levels accounted for 28% of the variance in unidimensional jet lag and 53% of the variance in multidimensional jet lag. It was concluded that there is a discordance between objective and subjective jet lag post-trip. Further, subjective jet lag in long-haul cabin crew is better explained by mood impairment than circadian phase. The results are discussed with reference to the gap between subjective and objective jet lag and the role of psychology rather than just biology in the jet lag experience. The implications for improving health and safety in the workplace, through a better understanding of the role of human factors in the management of jet lag, are discussed.

Sleep timing, chronotype and social jetlag: Impact on cognitive abilities and psychiatric disorders.

Sleep timing is controlled by the subtle interplay between circadian and homeostatic oscillators which, according to their endogenous properties, allow beings to feel spontaneously that it is time to go to bed or wake up in synchrony with the earth's light/dark cycle. In humans, however, social time and nocturnal artificial light modify sleep timing. Our modern lifestyle and artificial nocturnal light delay our bedtime, make us wake up, and lead to a greater intraindividual variability in sleep timing. Depending on the constraints that social time places on us, our sleep timing may be in or out of phase with the internal circadian timing determined by the circadian clock. When a person's social time is out of phase with their circadian time, they may be considered to suffer from circadian disruption or 'social jetlag'. There are interindividual differences in sleep timing that are known as morningness-eveningness preferences or chronotype, e.g. late chronotypes go to bed later. Chronotype may be assessed in terms of differences in kinetic homeostatic sleep pressure, intrinsic circadian period (ICP) and/or phase angle entrainment. In addition, chronotype depends on genetic and age-related factors, e.g. it gets earlier as people grow older. The social time of late chronotype individuals during week days is not adapted to their circadian time, unlike on free days. This results in social jetlag and circadian disruption, which in turn induces a chronic sleep debt due to a late bedtime and an early wake time, which is compensated on free days but only partially. Sleep and circadian clock disruption generally alter cognitive performance (alertness, attention, memory, higher-order executive functions such as response inhibition and decision-making) but their impact remains to be clarified. When subjects adopt their preferred sleep timing, a "synchrony effect" often appears with chronotypes performing better during daytime at optimal than at suboptimal timing (late chronotypes perform better in the evening, early chronotypes in the morning). Evening types appear to be cognitively more vulnerable to suboptimal times than morning types, probably because they have to deal with social jetlag and the "wake effort" period after awakening. Circadian disruption, but not chronotype, may impact attentional/inhibitory performance (more impulsivity and inattention). Strong associations have been found between mood disorders or attention deficit hyperactivity disorder (ADHD) and chronotype, with these psychiatric disorders typically being overrepresented in evening types. The association between social jetlag and these psychiatric disorders is less obvious. Social jetlag can be corrected by reducing exposure to evening light, although eveningness may be considered as a lifelong factor predisposing to depression or inattention.

The impact of social jetlag and chronotype on attention, inhibition and decision making in healthy adults.

Sleep and circadian clock disruption are associated with neuropsychiatric disorders, such as attention deficit hyperactivity disorder, but the impact on neurocognitive performance is unclear. We assessed whether chronotype and everyday circadian misalignment manifested as social jetlag were associated with inter-individual neurocognitive performance across domains of attention, inhibitory control and decision making. One hundred and eighty-eight healthy young adults were assessed for sleep and circadian properties and performed two neurocognitive tasks, the Continuous Performance Test and the Iowa Gambling Task. Social jetlag was associated with significantly faster and less variable reaction times and commission errors on the Continuous Performance Test. Poorer subjective sleep quality was associated with poorer decision making on the Iowa Gambling Task. No effects were present for polymorphisms in the circadian clock genes CLOCK and PER3. We conclude that circadian disruption shaped by everyday environmental factors may impact on attentional/inhibitory performance but not on a measure of risky decision making.

Chronotype is associated with psychological well-being depending on the composition of the study sample.

Past studies examining the effect of chronotype and social jetlag on psychological well-being have been inconsistent so far. Here, we recruited participants from the general population and enquired about their natural sleeping behavior, sleep quality, depressive symptoms, and perceived stress. Partial correlations were computed between sleep variables and indicators of psychological well-being, controlling for age and sex. Less sleep during work days was found a good indicator for impairments in psychological well-being. In exploratory follow-up analyses, the same correlations were calculated within groups of early, intermediate, and late chronotype. We observed that the composition of the sample in terms of chronotype influenced whether associations between sleep variables and psychological well-being could be observed, a finding that is advised to be taken into account in future studies.

Sleep Hygiene for Optimizing Recovery in Athletes: Review and Recommendations.

For elite athletes who exercise at a high level, sleep is critical to overall health. Many studies have documented the effects of sleep deprivation in the general population, but few studies exist regarding specific effects in the athlete. This review summarizes the effects of sleep deprivation and sleep extension on athletic performance, including reaction time, accuracy, strength and endurance, and cognitive function. There are clear negative effects of sleep deprivation on performance, including reaction time, accuracy, vigor, submaximal strength, and endurance. Cognitive functions such as judgment and decision-making also suffer. Sleep extension can positively affect reaction times, mood, sprint times, tennis serve accuracy, swim turns, kick stroke efficiency, and increased free throw and 3-point accuracy. Banking sleep (sleep extension prior to night of intentional sleep deprivation before sporting event) is a new concept that may also improve performance. For sports medicine providers, the negative effects of sleep deprivation cannot be overstated to athletes. To battle sleep deprivation, athletes may seek supplements with potentially serious side effects; improving sleep quality however is simple and effective, benefiting not only athlete health but also athletic performance.

The elite athlete as a special risk traveler and the jet lag's effect: lessons learned from the past and how to be prepared for the next Olympic Games 2020 Tokyo.

BACKGROUND: Elite athletes have to travel long-haul distances and cross multiple meridians; thus, a unique syndrome named as jet-lag is induced. Furthermore, traveler athletes are submitted to several factors negatively affecting their well-being and athletic performance. This qualitative descriptive study aims to promote safely and future promising participations of elite athletes in great events, such as the next Olympic Games 2020 Tokyo, based on the chronobiology of jet-lag, factors affecting the traveler athlete and previous experiences from the 2014 FIFA World Cup Brazil, the 2018 FIFA World Cup Russia and the Olympic Games Rio 2016. METHODS: A narrative review of the literature across a broad cross-section of the chronobiology of jet-lag and factors affecting the traveler athlete was undertaken. In addition, a general analysis based on the past sport events aforementioned is also included. RESULTS: The jet-lag disorder may occur after transmeridian travel over more than three time-zones and the resynchronization is dependent on the direction and number of the time-zones crossed and the availability and the intensity of local circadian time cues. Also the athlete's ability to sleep, eat, get hydrated and train, are essential, as well as, others individual tolerance differences, such as age, gender, chronotype and ethnic differences. Athletes should arrive a number of days before the competition according to the number of time-zone transitions experienced. CONCLUSIONS: Jet-lag is usually benign and self-limited, but can occasionally have serious consequences for the athlete's mental and physical health and performance. A good plan concerning the athlete's traveling schedule, sleeping, eating and training before and after travelling is mandatory.

Shift work, sleep disturbances and social jetlag in healthcare workers.

The aim of this study was to compare chronotype- and age-dependent sleep disturbances and social jetlag between rotating shift workers and non-shift workers, and between different types of shifts. In the Klokwerk+ cohort study, we included 120 rotating shift workers and 74 non-shift workers who were recruited from six Dutch hospitals. Participants wore Actigraph GT3X accelerometers for 24 hr for 7 days. From the Actigraph data, we predicted the sleep duration and social jetlag (measure of circadian misalignment). Mixed models and generalized estimation equations were used to compare the sleep parameters between shift and non-shift workers. Within shift workers, sleep on different shifts was compared with sleep on work-free days. Differences by chronotype and age were investigated using interaction terms. On workdays, shift workers had 3.5 times (95% confidence interval: 2.2-5.4) more often a short (< 7 hr per day) and 4.1 times (95% confidence interval: 2.5-6.8) more often a long (≥ 9 hr per day) sleep duration compared with non-shift workers. This increased odds ratio was present in morning chronotypes, but not in evening chronotypes (interaction p-value < .05). Older shift workers (≥ 50 years) had 7.3 times (95% confidence interval: 2.5-21.8) more often shorter sleep duration between night shifts compared with work-free days, while this was not the case in younger shift workers (< 50 years). Social jetlag due to night shifts increased with increasing age (interaction p-value < .05), but did not differ by chronotype (interaction p-value ≥ .05). In conclusion, shift workers, in particular older workers and morning chronotypes, experienced more sleep disturbances than non-shift workers. Future research should elucidate whether these sleep disturbances contribute to shift work-related health problems.

Sociodemographic and behavioural correlates of social jetlag in Australian adults: results from the 2016 National Sleep Health Foundation Study.

Social jetlag is a term used to describe misalignment between biological and social time. Measured as the difference in sleep midpoints between work and free days, social jetlag has been associated with unhealthy lifestyle behaviours and adverse health outcomes. This study aimed to identify the prevalence of social jetlag, and its sociodemographic and behavioural correlates in 837 respondents who completed the Sleep Health Foundation Australia 2016 online survey. Binomial logistic regression models determined associations between social jetlag and self-reported lifestyle and work outcomes, excluding night, evening or rotating shift workers. One third (31.1%) of respondents experienced >1h of social jetlag. In analyses adjusted for sociodemographic variables associated with social jetlag (age, marital status, work status and metropolitan living plus the significant interaction term for age by metro living), social jetlag was associated with longer sleep duration on free days (OR = 2.8, CI = 1.9-4.1), evening preference (OR = 2.0, CI = 1.4-2.4), often staying up later than planned on work days (OR 1.9, CI = 1.3-2.9), and having a computer (OR = 1.7, CI = 1.2-2.4) or phone (OR = 1.6, CI = 1.1-2.4) in the bedroom and internet use in the hour before bed (OR = 1.7, CI 1.2-2.5). Almost twice as many working respondents with social jetlag reported going to work when they should have taken sick leave due to their state of health (OR = 1.9, CI = 1.3-3.0). In conclusion, social jetlag is prevalent in the Australian community and associated with bedtime technology use. Work attendance when in poor health is cause for concern in Australian day workers and requires further investigation.

[CME: Jet Lag Jetlag]. / CME: Jetlag CME-Fragen.

CME: Jet Lag Jetlag Abstract. Crossing several time zones by air travel leads to a temporary desynchronization of the internal clock with the external light/dark cycle. In the following jet lag occurs typically including difficulties falling asleep or waking up early as well as day-time sleepiness and significant reduction of wellbeing and fitness. To provide optimal medical advice, it is necessary to understand the human circadian rhythm and sleep-wake regulation. In consideration with additional information on travel plans, an approach to alleviate jet lag symptoms can be developed. This article addresses different supportive measures and advice on how to adjust to a new time zone and reduce jet lag symptoms.

Greater circadian disadvantage during evening games for the National Basketball Association (NBA), National Hockey League (NHL) and National Football League (NFL) teams travelling westward.

We investigated the effects of a circadian disadvantage (i.e. playing in a different time zone) on the winning percentages in three major sport leagues in North America: the National Basketball Association, the National Hockey League and the National Football League. We reviewed 5 years of regular season games in the National Basketball Association, National Hockey League and National Football League, and noted the winning percentage of the visiting team depending on the direction of travel (west, east, and same time zone) and game time (day and evening games). T-tests and analysis of variance were performed to evaluate the effects of the circadian disadvantage, its direction, the number of time zones travelled, and the game time on winning percentages in each major league. The results showed an association between the winning percentages and the number of time zones traveled for the away evening games, with a clear disadvantage for the teams travelling westward. There was a significant difference in the teams' winning percentages depending on the travelling direction in the National Basketball Association (F2,5908  = 16.12, P < 0.0001) and the National Hockey League (F2,5639  = 4.48, P = 0.011), and a trend was found in the National Football League (F2,1279  = 2.86, P = 0.058). The effect of the circadian disadvantage transcends the type of sport and needs to be addressed for greater equity among the western and eastern teams in professional sports. These results also highlight the importance of circadian rhythms in sport performance and athletic competitions.

Computing sleep deficiency.

Sleep deficiency is a major public health concern. Since epidemiological studies play an important role in public health evaluations, this theoretical paper pursues answers to the question: 'How can we compute sleep deficiency as informative measures of exposures or doses in observational research?' Starting from the social jetlag concept and based on the chronodisruption rationale, we illustrate and discuss five approaches (one established and four untested, each with unique strengths and limitations) to quantify sleep deficiency by focusing on the timing and duration of sleep. Hitherto, social jetlag and chronodisruption rationale were neither explicitly proposed nor developed as assessments of sleep deficiency but, as we suggest, could potentially be utilized to this end. This first foray into computing sleep deficiency in epidemiological studies makes clear that laboratory, field and epidemiological collaboration is pre-requisite to elucidating potential (co-)causal roles of sleep deficiency in disease endpoints.

Greater Effect of East versus West Travel on Jet Lag, Sleep, and Team Sport Performance.

PURPOSE: This study aimed to determine the recovery timeline of sleep, subjective jet lag and fatigue, and team sport physical performance after east and west long-haul travel. METHODS: Ten physically trained men underwent testing at 0900 h and 1700 h local time on four consecutive days 2 wk before outbound travel (BASE), and the first 4 d after 21 h of outbound (WEST) and return (EAST) air travel across eight time zones between Australia and Qatar. Data collection included performance (countermovement jump, 20-m sprint, and Yo-Yo intermittent recovery level 1 [YYIR1] test) and perceptual (jet lag, motivation, perceived exertion, and physical feeling) measures. In addition, sleep was measured via wrist activity monitors and self-report diaries throughout the aforementioned data collection periods. RESULTS: Compared with the corresponding day at BASE, the reduction in YYIR1 distance after EAST was significantly different from the increase in WEST on day 1 after travel (P < 0.001). On day 2, significantly slower 20-m sprint times were detected in EAST compared with WEST (P = 0.03), with large effect sizes (ES) also indicating a greater reduction in YYIR1 distance in EAST compared with WEST (d = 1.06). Mean sleep onset and offset were significantly later and mean time in bed and sleep duration were significantly reduced across the 4 d in EAST compared with BASE and WEST (P < 0.05). Lastly, mean jet lag, fatigue, and motivation ratings across the 4 d were significantly worse in EAST compared with BASE and WEST (P < 0.05) and WEST compared with BASE (P < 0.05). CONCLUSIONS: Long-haul transmeridian travel can impede team sport physical performance. Specifically, east travel has a greater detrimental effect on sleep, subjective jet lag, fatigue, and motivation. Consequently, maximal and intermittent sprint performance is also reduced after east travel, particularly within 72 h after arrival.

Predicting jet lag in long-haul cabin crew: The role of illness cognitions and behaviour.

OBJECTIVE: Established risk factors for jet lag are mostly physiological including circadian preference, age, gender, the number of flight zones crossed and to some extent direction of travel. Some research has also highlighted a role for psychosocial factors including sleep, diet and 'circadian' health behaviours and illness cognitions although this remains relatively untested. The aim of this study was to evaluate the role of sleep, diet and illness cognitions in predicting perceived jet lag amongst long-haul crew. DESIGN: Sixty long-haul crew took part in a longitudinal study. Profile characteristics (including chronotype), preparation strategies (sleep, eating and 'circadian' behaviours) and illness cognitions were measured at baseline (before a trip). MAIN OUTCOME MEASURES: Subjective jet lag (unidimensional and multidimensional) was measured on the crews' second day off (post-trip). RESULTS: Hierarchical regression analyses showed that unidimensional jet lag was predicted by the belief in a cyclical timeline, whereas multidimensional jet lag was predicted by multidimensional jet lag at baseline and to a lesser extent by identity. No role was found for profile characteristics and preparation strategies. CONCLUSION: Illness cognitions partly explain the experience of perceived jet lag in long-haul cabin crew indicating that jet lag is in part a psycho-social construct, not just a biological one.

The impact of an implementation intention to improve mealtimes and reduce jet lag in long-haul cabin crew.

OBJECTIVE: Jet lag is common place amongst long-haul cabin crew. Timed food has been shown to reset the circadian rhythm in rodents. Implementation intentions have been used to change eating behaviour. Mealtimes could therefore be used as a countermeasure to reduce jet lag and improve alertness in long-haul cabin crew through forming an implementation intention to improve the regularity of meals on days off. DESIGN: Sixty long-haul crew took part in a randomised controlled trial, with two conditions: forming an implementation intention to eat regular meals on days off vs. no implementation intention. Pre-intervention measurements were taken at baseline (before a long-haul trip) and post-intervention measures were taken on the first and second days off post-trip. MAIN OUTCOME MEASURES: Subjective jet lag (unidimensional and multidimensional) and objective alertness (Psychomotor Vigilance Task (PVT)). RESULTS: Mixed ANOVA showed a significant condition x time interaction for unidimensional jet lag but not for multidimensional jet lag and objective alertness. In particular, the formation of an implementation intention to alter mealtimes resulted in a reduction of unidimensional jet lag. CONCLUSION: Implementation intentions can be used to alleviate jet lag in long-haul crew through promoting a change in mealtimes.

Insomnia, Nightmares, and Chronotype as Markers of Risk for Severe Mental Illness: Results from a Student Population.

STUDY OBJECTIVES: To group participants according to markers of risk for severe mental illness based on subsyndromal symptoms reported in early adulthood and evaluate attributes of sleep across these risk categories. METHODS: An online survey of sleep and psychiatric symptomatology (The Oxford Sleep Survey) was administered to students at one United Kingdom university. 1403 students (undergraduate and postgraduate) completed the survey. The median age was 21 (interquartile range = 20-23) and 55.60% were female. The cross-sectional data were used to cluster participants based on dimensional measures of psychiatric symptoms (hallucinations, paranoia, depression, anxiety, and (hypo)mania). High, medium, and low symptom groups were compared across sleep parameters: insomnia symptoms, nightmares, chronotype, and social jet lag. RESULTS: Insomnia symptoms, nightmares frequency, and nightmare-related distress increased in a dose-response manner with higher reported subsyndromal psychiatric symptoms (low, medium, and high). The high-risk group exhibited a later chronotype (mid sleep point for free days) than the medium- or low-risk group. The majority of participants (71.7%) in the high-risk group screened positive for insomnia and the median nightmare frequency was two per 14 days (moderately severe pathology). CONCLUSIONS: Insomnia, nightmares, and circadian phase delay are associated with increased subsyndromal psychiatric symptoms in young people. Each is a treatable sleep disorder and might be a target for early intervention to modify the subsequent progression of psychiatric disorder.

Effect of transmeridian travel and jetlag on mood disorders: evidence and implications.

OBJECTIVES: Given the sensitivity of individuals with mood disorders to circadian disruption, transmeridian travel would likely be a high-risk endeavour leading to onset or relapses in mood. A systematic review was undertaken to identify the evidence of the impact of transmeridian travel on people with mood disorders. METHODS: Databases search included the following: CINAHL, MEDLINE, PsycINFO and manual searching using the keywords jetlag, transmeridian travel, circadian rhythm disruption, mood disorder, bipolar, major depression, seasonal affective disorder, depression, mania and hypomania. RESULTS: Only three studies were identified that related to transmeridian travel and jetlag in people with mood disorders. There is some suggestion that transmeridian travel does appear to precipitate mood episodes with an increased rate of episodes of depression with westward compared with an increased rate of manic/hypomanic episodes with eastward travel. Individuals with a previous history of mood disorder appear to be more vulnerable if adherence to medication is compromised. CONCLUSION: Given the limited evidence that transmeridian travel precipitates mood episodes, this poses difficulties in identifying suitable ways to mitigate the effects of transmeridian travel in mood disorders. However, in the absence of mood-specific guidelines, some guidance can be given based on our current understanding of the relevance of circadian disruption to both jetlag and mood disorders. Further research is required to identify more focused strategies to mitigate the impact of transmeridian travel for individuals with mood disorders.

Social Jetlag, Chronotype, and Cardiometabolic Risk.

CONTEXT: Shift work, which imposes a habitual disruption in the circadian system, has been linked to increased incidence of cardiometabolic diseases, and acute circadian misalignment alters various metabolic processes. However, it remains unclear whether day-to-day circadian dysregulation contributes to these risks beyond poor sleep and other behavioral characteristics. OBJECTIVE: Individuals differ in circadian phase preference, known as chronotype, but may be constrained by modern work obligations to specific sleep schedules. Individuals experience social jetlag (SJL) due to a habitual discrepancy between their endogenous circadian rhythm and actual sleep times imposed by social obligations. Here, we examined whether chronotype and/or SJL associate with components of cardiovascular disease risk beyond the known effects of sleep disturbances, poor health behaviors, and depressive symptomatology. DESIGN: Participants were healthy, midlife adults who worked part- or full-time day shifts (n = 447; mean age, 42.7 [range, 30-54] y; 53% female; 83% white). Chronotype was assessed with the Composite Scale of Morningness. SJL was quantified as the difference (in minutes) between the midpoints of actigraphy-derived sleep intervals before work vs non-workdays. RESULTS: Multiple regression analyses showed that SJL related to a lower high-density lipoprotein-cholesterol level, higher triglycerides, higher fasting plasma insulin, insulin resistance, and adiposity (P < .05), even after adjustment for subjective sleep quality, actigraphy-derived sleep characteristics, depressive symptomatology, and health behaviors. Evening chronotype associated with lower high-density lipoprotein-cholesterol after adjustment for covariates. CONCLUSION: Our findings suggest that a misalignment of sleep timing is associated with metabolic risk factors that predispose to diabetes and atherosclerotic cardiovascular disease.

[Risks of psychiatric decompensation in travel]. / Voyages et risques de décompensations psychiatriques.

In the general consideration of travel-related illnesses, not much attention is given to mental health, while a significant proportion is due to psychiatric problems. Any trip is a source of stress that may trigger or worsen mental disorders ranging from culture shock to a pathogenic trip via the classic pathological trip: for a tourist seeking exotic adventure, young people in initiatory journey, an expatriate, a political refugee or an immigrant in search of better economic conditions, any traveler may stumble upon the traces of his own family history or of his home culture fantasy, and show symptoms at some stage along his path of psychological disorders. Indeed every culture identify appointed destinations where its members are seemingly more likely to falter: the roads to the east or the search for paradise lost for westerners (the Florence syndrome, the India syndrome or the island syndrome), those of the West (the Japanese in Paris syndrome), or places rich with mystical associations: Mecca for Muslims, Benares for Hindis, Jerusalem for the monotheistic religions. A return to the home country is mostly a necessary requirement for the subject to regain a footing in his culture.

Aligning work and circadian time in shift workers improves sleep and reduces circadian disruption.

Sleep loss and circadian disruption-a state of misalignment between physiological functions and imposed sleep/wake behavior-supposedly play central roles in the etiology of shift work-related pathologies [1-4]. Circadian entrainment is, however, highly individual [5], resulting in different chronotypes [6, 7]. Chronotype in turn modulates the effects of working times: compared to late chronotypes, earlier ones sleep worse and shorter and show higher levels of circadian misalignment during night shifts, while late types experience more sleep and circadian disruption than early types when working morning shifts [8]. To promote sleep and reduce the mismatch between circadian and working time, we implemented a chronotype-adjusted (CTA) shift schedule in a factory. We abolished the most strenuous shifts for extreme chronotypes (i.e., mornings for late chronotypes, nights for early ones) and examined whether sleep duration and quality, social jetlag [9, 10], wellbeing, subjective stress perception, and satisfaction with leisure time improved in this schedule. Intermediate chronotypes (quartiles 2 and 3) served as a control group, still working morning (6:00-14:00), evening (14:00-22:00), and night (22:00-6:00) shifts, with two strenuous shifts (out of twelve per month) replaced by evening ones. We observed a significant increase of self-reported sleep duration and quality, along with increased wellbeing ratings on workdays among extreme chronotypes. The CTA schedule reduced overall social jetlag by 1 hr, did not alter stress levels, and increased satisfaction with leisure time (early types only). Chronotype-based schedules thus can reduce circadian disruption and improve sleep; potential long-term effects on health and economic indicators need to be elucidated in future studies.

Chronotype and stability of spontaneous locomotor activity rhythm in BMAL1-deficient mice.

Behavior, physiological functions and cognitive performance change over the time of the day. These daily rhythms are either externally driven by rhythmic environmental cues such as the light/dark cycle (masking) or controlled by an internal circadian clock, the suprachiasmatic nucleus (SCN), which can be entrained to the light/dark cycle. Within a given species, there is genetically determined variability in the temporal preference for the onset of the active phase, the chronotype. The chronotype is the phase of entrainment between external and internal time and is largely regulated by the circadian clock. Genetic variations in clock genes and environmental influences contribute to the distribution of chronotypes in a given population. However, little is known about the determination of the chronotype, the stability of the locomotor rhythm and the re-synchronization capacity to jet lag in an animal without a functional endogenous clock. Therefore, we analyzed the chronotype of BMAL1-deficient mice (BMAL1-/-) as well as the effects of repeated experimental jet lag on locomotor activity rhythms. Moreover, light-induced period expression in the retina was analyzed to assess the responsiveness of the circadian light input system. In contrast to wild-type mice, BMAL1-/- showed a significantly later chronotype, adapted more rapidly to both phase advance and delay but showed reduced robustness of rhythmic locomotor activity after repeated phase shifts. However, photic induction of Period in the retina was not different between the two genotypes. Our findings suggest that a disturbed clockwork is associated with a late chronotype, reduced rhythm stability and higher vulnerability to repeated external desynchronization.