Social jetlag: misalignment of biological and social time

Humans show large differences in the preferred timing of their sleep and activity. This so-called "chronotype" is largely regulated by the circadian clock. Both genetic variations in clock genes and environmental influences contribute to the distribution of chronotypes in a given population, ranging from extreme early types to extreme late types with the majority falling between these extremes. Social (e.g., school and work) schedules interfere considerably with individual sleep preferences in the majority of the population. Late chronotypes show the largest differences in sleep timing between work and free days leading to a considerable sleep debt on work days, for which they compensate on free days. The discrepancy between work and free days, between social and biological time, can be described as 'social jetlag.' Here, we explore how sleep quality and psychological wellbeing are associated with individual chronotype and/or social jetlag. A total of 501 volunteers filled out the Munich ChronoType Questionnaire (MCTQ) as well as additional questionnaires on: (i) sleep quality (SF-A), (ii) current psychological wellbeing (Basler Befindlichkeitsbogen), (iii) retrospective psychological wellbeing over the past week (POMS), and (iv) consumption of stimulants (e.g., caffeine, nicotine, and alcohol). Associations of chronotype, wellbeing, and stimulant consumption are strongest in teenagers and young adults up to age 25 yrs. The most striking correlation exists between chronotype and smoking, which is significantly higher in late chronotypes of all ages (except for those in retirement). We show these correlations are most probably a consequence of social jetlag, i.e., the discrepancies between social and biological timing rather than a simple association to different chronotypes. Our results strongly suggest that work (and school) schedules should be adapted to chronotype whenever possible.     

Social Jetlag: Misalignment of Biological and Social Time

Humans show large differences in the preferred timing of their sleep and activity. This so‐called “chronotype” is largely regulated by the circadian clock. Both genetic variations in clock genes and environmental influences contribute to the distribution of chronotypes in a given population, ranging from extreme early types to extreme late types with the majority falling between these extremes. Social (e.g., school and work) schedules interfere considerably with individual sleep preferences in the majority of the population. Late chronotypes show the largest differences in sleep timing between work and free days leading to a considerable sleep debt on work days, for which they compensate on free days. The discrepancy between work and free days, between social and biological time, can be described as ‘social jetlag.’ Here, we explore how sleep quality and psychological wellbeing are associated with individual chronotype and/or social jetlag. A total of 501 volunteers filled out the Munich ChronoType Questionnaire (MCTQ) as well as additional questionnaires on: (i) sleep quality (SF‐A), (ii) current psychological wellbeing (Basler Befindlichkeitsbogen), (iii) retrospective psychological wellbeing over the past week (POMS), and (iv) consumption of stimulants (e.g., caffeine, nicotine, and alcohol). Associations of chronotype, wellbeing, and stimulant consumption are strongest in teenagers and young adults up to age 25 yrs. The most striking correlation exists between chronotype and smoking, which is significantly higher in late chronotypes of all ages (except for those in retirement). We show these correlations are most probably a consequence of social jetlag, i.e., the discrepancies between social and biological timing rather than a simple association to different chronotypes. Our results strongly suggest that work (and school) schedules should be adapted to chronotype whenever possible.     

CHRONOTYPES AND SUBJECTIVE SLEEP PARAMETERS IN EPILEPSY PATIENTS: A LARGE QUESTIONNAIRE STUDY

Accumulating evidence suggests epilepsy and seizures may influence circadian rhythms and that circadian rhythms may influence epilepsy. It is also conceivable that seizure timing influences the timing of daily activities, sleeping, and wakefulness (i.e., chronotype). Only one group has studied the distribution of chronotypes of epileptics, showing significant differences between the diurnal activity patterns in two groups of patients with different epilepsy syndromes. The authors performed a questionnaire-based study of 200 epilepsy patients to compare the distribution of chronotypes and subjective sleep parameters of sleep duration and time of mid-sleep on free days to the distribution in the general population (n?=?4042). Within this large group of epilepsy patients, we also compared the chronotypes of subsamples with well-defined epilepsy syndromes, i.e., temporal lobe epilepsy [TLE; n?=?46], frontal lobe epilepsy [FLE; n?=?30], and juvenile myoclonic epilepsy [JME; n?=?38]. In addition, 27 patients who had had surgery for TLE were compared with those with TLE who had not had surgery. Both the Morningness-Eveningness Questionnaire and Munich Chronotype Questionnaire were used to determine chronotypes and subjective sleep parameters. Significant differences in morningness/eveningness distribution, timing of mid-sleep (corrected for sleep duration), and total sleep time on free days were found between epileptics and healthy controls. Those with epilepsy were more morning oriented, had earlier mid-sleep on free days, and longer sleep duration on free days (p?<?.001). However, distributions of chronotypes and sleep parameters between the groups of people with TLE, FLE, and JME did not differ. Persons who had surgery for TLE had similar morningness-eveningness parameters and similar sleep durations compared to those without surgery, but mid-sleep on free days was earlier in operated patients (p?=?.039). In conclusion, this is the first large study focusing on chronotypes in people with epilepsy. We show that the distribution of chronotypes and subjective sleep parameters of epileptics, in general, is different from that of healthy controls. Nevertheless, no differences are observed between patients with specified epilepsy syndromes, although they exhibit seizures with different diurnal patterns. Our results suggest that epilepsy, itself, rather than seizure timing, has a significant influence on chronotype behavior and subjective sleep parameters. (Author correspondence: w.hofstra@mst.nl)     

Sleep/wake patterns and circadian typology in preschool children based on standardized parental self-reports

We studied the sleep/wake patterns and circadian typology of Japanese preschool children living in the Tokyo metropolitan area (193 boys and 190 girls, 4–6 years of age) from June to July 2012 based on a standardized parental self-reporting questionnaire. Our major findings are as follows: (1) sleep/wake timing was delayed, and the duration of nocturnal sleep (sleep period as well as time in bed) increased from that on scheduled days (weekdays) to that on free days (weekends) for all ages. (2) The duration of daily sleep (24?h), including daytime nap, was longer for 4-year-old children compared with that in 5- to 6-year-old children, but not significantly different between scheduled and free days within each age group. (3) The distribution of chronotypes was 36.3% for morning (M)-type, 48.8% for neither (N)-type and 11.2% for evening (E)-type, and this distribution was independent of sex or age. (4) Sleep/wake timing delays were observed from M-type and N-type to E-type during scheduled and free days. (5) The duration of nocturnal sleep decreased but increased for 24-h sleep time from M-type and N-type to E-type on scheduled days. (6) Sleep durations did not differ among chronotypes on free days. (7) Chronotypes were associated with parents’ diurnal preferences, mealtimes and attendance at kindergartens or childcare centers but not with sex, age, season of birth, exposure to multimedia or exposure to morning sunlight in their bedrooms. When these results were compared with those for older children and adolescents, similar sleep/wake patterns and circadian typology were observed, although to a lesser degree, in children as young as 4–6 years of age. Napping may compensate, in part, for an accumulated weekday sleep deficit. The distribution of chronotypes was associated with differences in sleep/wake timing and duration and was influenced by the parents’ diurnal preferences and lifestyles. Further research on preschool children is required to investigate whether circadian typology affects their behavioral, emotional and cognitive development.     

Morningness‐Eveningness Comparison in Adolescents from Different Countries around the World

Very few studies have focused on differences in chronotype around the globe. In this study, morningness‐eveningness was measured using the Composite Scale of Morningness and the midpoint of sleep on free days (corrected for sleep debt, MSF_sc) in adolescents of sixteen German schools abroad, dispersed all over the world, and for comparison pupils attending German schools. There was no influence of duration of residence in the respective locality, and sex differences were weak. Age correlated negatively with morningness. A significant influence of climate zone (temperate, subtropics, tropics) was found, with adolescents in the subtropics being the latest chronotypes, and an interaction of age×climate zone was identified. Significant associations between chronotype and longitude and latitude were identified within the time zone of central Europe. Adolescents were found to be more morning oriented both toward the East and North. The results indicate that climate, longitude, and latitude contribute to chronotype.     

Fibromyalgia syndrome and chronotype: late chronotypes are more affected

Sleep has strong links to the symptomology of fibromyalgia syndrome (FMS), a diffuse musculoskeletal pain disorder. Information about the involvement of the circadian clock is, however, sparse. In this study, 1548 individuals with FMS completed an online survey containing questions on demographics, stimulant consumption, sleep quality, well-being and subjective pain, chronotype (assessed by the Munich ChronoType Questionnaire, MCTQ), and FMS impact. Chronotype (expressed as the mid-sleep-point on free days, corrected for sleep deficit on workdays, MSF(sc)) significantly correlated with stress-ratings, so-called "memory failures in everyday life," fatigue, FMS impact, and depression but not with anxiety. When chronotypes were categorized into 3 groups (early, intermediate, late), significant group differences were found for sum scores of perceived stress, memory failures in everyday life, fatigue, FMS impact, and depression but not anxiety, with late chronotypes being more affected than early chronotypes. Sleepiness ratings were highest in early chronotypes. Challenges of sleep quality and subjective pain were significantly increased in both early and late chronotypes. The results show that according to their reports, late chronotypes are more affected by fibromyalgia.     

Individual Traits and Environmental Factors Influencing Sleep Timing: A Study of 225 Japanese Couples

Behavioral and physiological processes, such as sleep-wakefulness, thermoregulation, and hormone secretion, exhibit 24-h rhythms in most organisms. These biological rhythms are driven by the circadian clock system and are entrained by the external environment, which in the case of humans includes social time schedules. Couples might be ideal experimental subjects to discriminate between individual traits and environmental factors, as they share lifestyle habits but not genetic backgrounds. In this study, sleep timing was compared between married Japanese couples (n?=?225) who had lived together for 1 yr or more (mean 17 yrs). Additionally, the authors evaluated the influence of individual traits and environmental factors on an individual's sleep timing per each couple. The results reveal that the sleep timings of a couple are mainly associated with the chronotypes of the husband and wife, whereas the sleep timings are significantly influenced by certain environmental factors. The findings suggest that chronotype remains one of the major determinants of an individual's sleep onset and wake times. Understanding an individual's chronotype may help improve the quality of life issues surrounding sleep. (Author correspondence: mishima@ncnp.go.jp)     

Shift-specific associations between age,chronotype and sleep duration

The objective of this study was to examine the association of age with chronotype and sleep duration in day workers and rotating shift workers, including night shift work. Between October 2012 and February 2015, a cross-sectional study was conducted in a German chemical company. Using the “Munich ChronoType Questionnaire” (MCTQ), data about sleep onset and sleep offset during workdays and work-free days were retrieved and the chronotype was computed during regular voluntary occupational health check-ups. Associations between age and chronotype, as well as sleep duration, were assessed using linear regression analyses. Potential effect modification by the working time system was examined. Within the study period, 4,040 employees (82.3% and 17.7% were engaged in day work and rotating shift work, respectively) completed the questionnaire. Study participants were on average 41.8 years old (Min = 18.0, Max = 65.0, SD = 10.2) and predominantly male (75.4%). Mean chronotype and overall sleep duration was 03:22 (SD = 54 min) and 7.2 h (SD = 1.0 h) respectively. Older age was associated with earlier chronotype and reduced overall sleep duration in both day workers and rotating shift workers (p < 0.001 for all models). Compared to day workers, employees whom engaged in rotating shift work were later chronotypes and had overall a longer sleep duration. With older age, the difference between day and rotating shift workers regarding chronotype increased, while the difference regarding overall sleep duration decreased (p_interaction<0.005 for both models). This finding could indicate that both changes in circadian physiology and exposure to certain work schedules contribute to the age-related changes. Older rotating shift workers, with early chronotypes may have issues with night shifts, while day work and morning shifts may be best compatible to earlier chronotypes. Differences in sleep timing across age groups, might indicate that the same work hours will affect shift workers differently, dependent on their age, suggesting that more flexible and chronotype-adapted work hours could provide useful; especially for older employees. Sleep education in the form of courses and health campaigns could be a way to raise awareness of the importance of a healthy sleep pattern. This could be achieved by learning strategies to better adjust individual sleep patterns to work hours.     

Chronotype and sleep duration: The influence of season of assessment

Little is known about human entrainment under natural conditions, partly due to the complexity of human behavior, torn between biological and social time and influenced by zeitgebers (light–dark cycles) that are progressively “polluted” (and thereby weakened) by artificial light. In addition, data about seasonal variations in sleep parameters are scarce. We, therefore, investigated seasonal variation in cross-sectional assessments of sleep/wake times of 9765 subjects from four European populations (EGCUT?=?Estonian Genome Centre, University of Tartu in Estonia; KORA?=?Cooperative Health Research in the Region of Augsburg in Germany; KORCULA?=?The Korcula study in Croatia; and ORCADES?=?The Orkney Complex Disease Study in Scotland). We identified time-of-year dependencies for the distribution of chronotype (phase of entrainment assessed as the mid-sleep time point on free days adjusted for sleep deficit of workdays) in cohorts from Estonia (EGCUT) and Germany (KORA). Our results indicate that season (defined as daylight saving time – DST and standard zonetime periods – SZT) specifications of photoperiod influence the distribution of chronotype (adjusted for age and sex). Second, in the largest investigated sample, from Estonia (EGCUT; N?=?5878), we could detect that seasonal variation in weekly average sleep duration was dependent on individual chronotype. Later chronotypes in this cohort showed significant variation in their average sleep duration across the year, especially during DST (1?h advance in social time from the end of March to end of October), while earlier chronotypes did not. Later chronotypes not only slept less during the DST period but the average chronotype of the population assessed during this period was earlier than during the SZT (local time for a respective time zone) period. More in detail, hierarchical multiple regression analyses showed that, beyond season of assessment (DST or SZT), social jetlag (SJl; the discrepancy between the mid sleep on free and work days – which varied with age and sex) contributed to a greater extent to the variation in sleep duration than chronotype (after taking into account factors that are known to influence sleep duration, i.e. age, sex and body mass index). Variation in chronotype was also dependent on age, sex, season of assessment and SJl (which is highly correlated with chronotype – SJl was larger among later chronotypes). In summary, subjective assessments of sleep/wake times are very reliable to assess internal time and sleep duration (e.g. reproducing sleep duration and timing tendencies related to age and sex across the investigated populations), but season of assessment should be regarded as a potential confounder. We identified in this study photoperiod (seasonal adaptation) and SJl as two main factors influencing seasonal variation in chronotype and sleep duration. In conclusion, season of assessment, sex and age have an effect on epidemiological variation in sleep duration, chronotype and SJl, and should be included in studies investigating associations between these phenotypes and health parameters, and on the development of optimal prevention strategies.     

Depression scores associate with chronotype and social jetlag in a rural population

In public health, mood disorders are among the most important mental impairments. Patients with depressive episodes exhibit daily mood variations, abnormal patterns in sleep-wake behavior, and in the daily rhythms of several endocrine-metabolic parameters. Although the relationship between the sleep/circadian processes and mood disorders is poorly understood, clock-related therapies, such as light therapy, sleep deprivation, and rigid sleep schedules, have been shown to be effective treatments. Several studies investigated the relationship between circadian phenotype (chronotype) and depression. These focused mainly on urban populations and assessed diurnal preferences (Morningness-Eveningness score) rather than the actual timing of sleep and activity. Here, we used the Beck Depression Inventory (BDI) in an essentially rural population (N?=?4051), and investigated its relation to circadian phenotype (chronotype and social jetlag), assessed with the Munich Chronotype Questionnaire (MCTQ). In our study design, we (i) normalized both chronotype and BDI scores for age and sex (MSF(sas) and BDI(as), respectively); (ii) calculated individual social jetlag (misalignment of the biological and social time); and (iii) investigated the relationship between circadian phenotypes and BDI scores in a population homogeneous in respect to culture, socioeconomic factors, and daily light exposure. A 15.65% (N?=?634) of the participants showed mild to severe depressive BDI scores. Late chronotypes had a higher BDI(as) than intermediate and early types, which was independent of whether or not the participants were smokers. Both chronotype and BDI(as) correlated positively with social jetlag. BDI(as) was significantly higher in subjects with >2?h of social jetlag than in the rest of the population?again independent of smoking status. We also compared chronotype and social jetlag distributions between BDI categories (no symptoms, minimal symptoms, and mild to severe symptoms of depression) separately for men and women and for four age groups; specifically in the age group 31?40 yrs, subjects with mild to severe BDI scores were significantly later chronotypes and suffered from higher social jetlag. Our results indicate that misalignment of circadian and social time may be a risk factor for developing depression, especially in 31- to 40-yr-olds. These relationships should be further investigated in longitudinal studies to reveal if reduction of social jetlag should be part of prevention strategies. (Author correspondence: karla.allebrandt@med.uni-muenchen.de ).     

Depression Scores Associate With Chronotype and Social Jetlag in a Rural Population

In public health, mood disorders are among the most important mental impairments. Patients with depressive episodes exhibit daily mood variations, abnormal patterns in sleep-wake behavior, and in the daily rhythms of several endocrine-metabolic parameters. Although the relationship between the sleep/circadian processes and mood disorders is poorly understood, clock-related therapies, such as light therapy, sleep deprivation, and rigid sleep schedules, have been shown to be effective treatments. Several studies investigated the relationship between circadian phenotype (chronotype) and depression. These focused mainly on urban populations and assessed diurnal preferences (Morningness-Eveningness score) rather than the actual timing of sleep and activity. Here, we used the Beck Depression Inventory (BDI) in an essentially rural population (N?=?4051), and investigated its relation to circadian phenotype (chronotype and social jetlag), assessed with the Munich Chronotype Questionnaire (MCTQ). In our study design, we (i) normalized both chronotype and BDI scores for age and sex (MSF_sas and BDI_as, respectively); (ii) calculated individual social jetlag (misalignment of the biological and social time); and (iii) investigated the relationship between circadian phenotypes and BDI scores in a population homogeneous in respect to culture, socioeconomic factors, and daily light exposure. A 15.65% (N?=?634) of the participants showed mild to severe depressive BDI scores. Late chronotypes had a higher BDI_as than intermediate and early types, which was independent of whether or not the participants were smokers. Both chronotype and BDI_as correlated positively with social jetlag. BDI_as was significantly higher in subjects with >2?h of social jetlag than in the rest of the population—again independent of smoking status. We also compared chronotype and social jetlag distributions between BDI categories (no symptoms, minimal symptoms, and mild to severe symptoms of depression) separately for men and women and for four age groups; specifically in the age group 31–40 yrs, subjects with mild to severe BDI scores were significantly later chronotypes and suffered from higher social jetlag. Our results indicate that misalignment of circadian and social time may be a risk factor for developing depression, especially in 31- to 40-yr-olds. These relationships should be further investigated in longitudinal studies to reveal if reduction of social jetlag should be part of prevention strategies. (Author correspondence: karla.allebrandt@med.uni-muenchen.de)     

Individual traits and environmental factors influencing sleep timing: a study of 225 Japanese couples

Behavioral and physiological processes, such as sleep-wakefulness, thermoregulation, and hormone secretion, exhibit 24-h rhythms in most organisms. These biological rhythms are driven by the circadian clock system and are entrained by the external environment, which in the case of humans includes social time schedules. Couples might be ideal experimental subjects to discriminate between individual traits and environmental factors, as they share lifestyle habits but not genetic backgrounds. In this study, sleep timing was compared between married Japanese couples (n?=?225) who had lived together for 1 yr or more (mean 17 yrs). Additionally, the authors evaluated the influence of individual traits and environmental factors on an individual's sleep timing per each couple. The results reveal that the sleep timings of a couple are mainly associated with the chronotypes of the husband and wife, whereas the sleep timings are significantly influenced by certain environmental factors. The findings suggest that chronotype remains one of the major determinants of an individual's sleep onset and wake times. Understanding an individual's chronotype may help improve the quality of life issues surrounding sleep.     

Chronotype and environmental light exposure in a student population

ABSTRACT

In humans and most other species, changes in the intensity and duration of light provide a critical set of signals for the synchronisation of the circadian system to the astronomical day. The timing of activity within the 24 h day defines an individual’s chronotype, i.e. morning, intermediate or evening type. The aim of this study was to investigate the associations between environmental light exposure, due to geographical location, on the chronotype of university students. Over 6 000 university students from cities in the Northern Hemisphere (Oxford, Munich and Groningen) and Southern Hemisphere (Perth, Melbourne and Auckland) completed the Munich ChronoType Questionnaire. In parallel, light measures (daily irradiance, timing of sunrise and sunset) were compiled from satellite or ground stations at each of these locations. Our data shows that later mid-sleep point on free days (corrected for oversleep on weekends MFS_sc) is associated with (i) residing further from the equator, (ii) a later sunset, (iii) spending more time outside and (iv) waking from sleep significantly after sunrise. However, surprisingly, MSF_sc did not correlate with daily light intensity at the different geographical locations. Although these findings appear to contradict earlier studies suggesting that in the wider population increased light exposure is associated with an earlier chronotype, our findings are derived exclusively from a student population aged between 17 and 26 years. We therefore suggest that the age and occupation of our population increase the likelihood that these individuals will experience relatively little light exposure in the morning whilst encountering more light exposure later in the day, when light has a delaying effect upon the circadian system.     

Chronotype in very low birth weight adults – a sibling study

ABSTRACT

Chronotype is the temporal preference for activity and sleep during the 24 h day and is linked to mental and physical health, quality of life, and mortality. Later chronotypes, so-called “night owls”, consistently display poorer health outcomes than “larks”. Previous studies have suggested that preterm birth (<37 weeks of gestation) is associated with an earlier chronotype in children, adolescents, and young adults, but studies beyond this age are absent. Our aim was to determine if adults born preterm at very low birth weight (VLBW, ≤1500 g) display different chronotypes than their siblings. We studied VLBW adults, aged 29.9 years (SD 2.8), matched with same-sex term-born siblings as controls. A total of 123 participants, consisting of 53 sibling pairs and 17 unmatched participants, provided actigraphy-derived data on the timing, duration, and quality of sleep from 1640 nights (mean 13.3 per participant, SD 2.7). Mixed effects models provided estimates and significance tests. Compared to their siblings, VLBW adults displayed 27 min earlier sleep midpoint during free days (95% CI: 3 to 51 min, p =.029). This was also reflected in the timing of falling asleep, waking up, and sleep-debt corrected sleep midpoint. The findings were emphasized in VLBW participants born small for gestational age. VLBW adults displayed an earlier chronotype than their siblings still at age 30, which suggests that the earlier chronotype is an enduring individual trait not explained by shared family factors. This preference could provide protection from risks associated with preterm birth.     

The stimulating effect of bright light on physical performance depends on internal time

The human circadian clock regulates the daily timing of sleep, alertness and performance and is synchronized to the 24-h day by the environmental light-dark cycle. Bright light exposure has been shown to positively affect sleepiness and alertness, yet little is known about its effects on physical performance, especially in relation to chronotype. We, therefore, exposed 43 male participants (mean age 24.5 yrs ± SD 2.3 yrs) in a randomized crossover study to 160 minutes of bright (BL: ≈ 4.420 lx) and dim light (DL: ≈ 230 lx). During the last 40 minutes of these exposures, participants performed a bicycle ergometer test. Time-of-day of the exercise sessions did not differ between the BL and DL condition. Chronotype (MSF(sc), mid-sleep time on free days corrected for oversleep due to sleep debt on workdays) was assessed by the Munich ChronoType Questionnaire (MCTQ). Total work was significantly higher in BL (median 548.4 kJ, min 411.82 kJ, max 875.20 kJ) than in DL (median 521.5 kJ, min 384.33 kJ, max 861.23 kJ) (p = 0.004) going along with increased exhaustion levels in BL (blood lactate (+12.7%, p = 0.009), heart rate (+1.8%, p = 0.031), and Borg scale ratings (+2.6%, p = 0.005)) in all participants. The differences between total work levels in BL and DL were significantly higher (p = 0.004) if participants were tested at a respectively later time point after their individual mid-sleep (chronotype). These novel results demonstrate, that timed BL exposure enhances physical performance with concomitant increase in individual strain, and is related not only to local (external) time, but also to an individual's internal time.     

Late emergence chronotypes of fruit flies Drosophila melanogaster exhibit higher accuracy of entrainment

Inter-individual variation in phase-of-entrainment (chronotype) is widely observed in many species, but the underlying mechanisms and its consequences remain largely unexplored. In light of considerable limitations of previous studies proposing that the late chronotypes exhibit weakly stable rhythms, we employed outbred Drosophila populations exhibiting early and late emergence chronotypes to re-visit such associations. Contrary to previous reports, we observed that the late chronotypes consistently exhibit higher stability in emergence and activity–rest rhythms as compared to the early chronotypes, both under laboratory and semi-natural conditions, which is not associated with higher precision of circadian clocks, thus demonstrating the existence of genetic correlations between accuracy of entrainment and chronotype. Our results, along with the previously reported clock property differences between the early and the late emergence chronotypes highlights a possible complex interplay of clock period, phase response curve and accuracy in determining phase-of-entrainment.     

The Relationship Between Breakfast Skipping,Chronotype, and Glycemic Control in Type 2 Diabetes

Breakfast skipping is associated with obesity and an increased risk of type 2 diabetes. Later chronotypes, individuals who have a preference for later bed and wake times, often skip breakfast. The aim of the study was to explore the relationships among breakfast skipping, chronotype, and glycemic control in type 2 diabetes patients. We collected sleep timing and 24-h dietary recall from 194 non-shift-working type 2 diabetes patients who were being followed in outpatient clinics. Mid-sleep time on free days (MSF) was used as an indicator of chronotype. Hemoglobin A1C (HbA_1C) values were obtained from medical records. Hierarchical linear regression analyses controlling for demographic, sleep, and dietary variables were computed to determine whether breakfast skipping was associated with HbA_1C. Additional regression analyses were performed to test if this association was mediated by chronotype. There were 22 participants (11.3%) who self-reported missing breakfast. Breakfast skippers had significantly higher HbA_1C levels, higher body mass indices (BMI), and later MSF than breakfast eaters. Breakfast skipping was significantly associated with higher HbA_1C values (B?=?0.108, p?=?0.01), even after adjusting for age, sex, race, BMI, number of diabetes complications, insulin use, depressive symptoms, perceived sleep debt, and percentage of daily caloric intake at dinner. The relationship between breakfast skipping and HbA_1C was partially mediated by chronotype. In summary, breakfast skipping is associated with a later chronotype. Later chronotype and breakfast skipping both contribute to poorer glycemic control, as indicated by higher HbA_1C levels. Future studies are needed to confirm these findings and determine whether behavioral interventions targeting breakfast eating or sleep timing may improve glycemic control in patients with type 2 diabetes.     

Chronotype and postmenopausal breast cancer risk among women in the California Teachers Study

ABSTRACT

Chronotype is the behavioral manifestation of an individual’s underlying circadian rhythm, generally characterized by one’s propensity to sleep at a particular time during the 24 hour cycle. Evening chronotypes (“night owls”) generally suffer from worse physical and mental health compared to morning chronotypes (“morning larks”) – for reasons that have yet to be explained. One hypothesis is that evening chronotypes may be more susceptible to circadian disruption, a condition where the coordinated timing of biologic processes breaks down. The role of chronotype as an independent or modifying risk factor for cancer has not been widely explored. The objective of the current study was to evaluate the risk of breast cancer associated with chronotype in a case-control study nested within the California Teachers Study (CTS) cohort. The study population consisted of 39686 post-menopausal CTS participants who provided information on chronotype by completing a questionnaire in 2012–2013. 2719 cases of primary invasive breast cancer diagnosed from 1995/1996 through completion of the chronotype questionnaire were identified by linkage of the CTS to the California Cancer Registry. 36967 CTS participants who had remained cancer-free during this same time period served as controls. Chronotype was ascertained by responses to an abbreviated version of the Horne-Ostberg Morningness-Eveningness Questionnaire (MEQ) and was characterized into five categories: definite morning, more morning than evening, neither morning or evening, more evening than morning, definite evening. Multivariable unconditional logistic regression analyses were performed to estimate the odds ratios (ORs) and 95% confidence intervals (95% CIs) for each of the chronotypes, adjusted for established breast cancer risk factors. Compared to definite morning types, definite evening types had an increased risk of breast cancer with elevated ORs that were statistically significant in both the crude (OR = 1.24, 95% CI: 1.10–1.40) and fully-adjusted models (OR = 1.20, 95% CI: 1.06–1.35). The risk estimates in the fully-adjusted model for all other chronotypes did not significantly differ from one. These results suggest that evening chronotype may be an independent risk factor for breast cancer among a population of women who are not known to have engaged in any substantial night shift work. Further research in other populations of non-shift workers is warranted.     

A unique,fast-forwards rotating schedule with 12-h long shifts prevents chronic sleep debt

Sleep debt – together with circadian misalignment – is considered a central factor for adverse health outcomes associated with shift work. Here, we describe in detail sleep-wake behavior in a fast-forward rotating 12-h shift schedule, which involves at least 24 hours off after each shift and thus allows examining the role of immediate recovery after shift-specific sleep debt. Thirty-five participants at two chemical plants in Germany were chronotyped using the Munich ChronoType Questionnaire for Shift-Workers (MCTQ^Shift) and wore actimeters throughout the two-week study period. From these actimetry recordings, we computed sleep and nap duration, social jetlag (a measure of circadian misalignment), and the daily timing of activity and sleep (center of gravity and mid-sleep, respectively). We observed that the long off-work periods between each shift create a fast alternation between shortened (mean ± standard deviation, 5h 17min ± 56min) and extended (8h 25min ± 72min) sleep episodes resulting in immanent reductions of sleep debt. Additionally, extensive napping of early chronotypes (up to 3 hours before the night shift) statistically compensated short sleep durations after the night shift. Partial rank correlations showed chronotype-dependent patterns of sleep and activity that were similar to those previously described in 8-h schedules; however, sleep before the day shift did not differ between chronotypes. Our findings indicate that schedules preventing a build-up of chronic sleep debt may reduce detrimental effects of shift work irrespective of shift duration. Prospective studies are needed to further elucidate the relationship between sleep, the circadian system, and health and safety hazards.