Relation of chronotype to sleep complaints in the general Finnish population

Individuals show variation in their preference for the daily timing of activities. In this study the authors analyzed whether chronotypes associate with sleep duration and sleep-related complaints. The authors used the National FINRISK Study 2007 Survey data on 3696 women and 3162 men, representative of the Finnish population aged 25 yrs and older, for the assessment of chronotype and self-reported sleep. Evening types experienced insomnia symptoms, had nightmares, and had used recently hypnotics significantly more often than other chronotypes among both men and women. In a multinominal logistic regression model predicting insufficient sleep, the association of eveningness with insufficient sleep was not abolished after adjustment for sex, age, and sleep duration. The prevalence of short sleepers was significantly higher in evening types among men than among women, whereas that of long sleepers was significantly higher in evening types among both men and women, as compared with the other chronotypes. These results indicate that eveningness predisposes individuals to a range of sleep complaints.     

Influence of Chronotype,Season, and Sex of Subject on Sleep Behavior of Young Adults

The aim of this study was to investigate whether sex, season, and/or chronotype influence the sleep behavior of university students. Detailed data were collected on activity/rest patterns by wrist actigraphy combined with diaries. Thirty‐four medical students (19 female and 15 male) were monitored by Actiwatch® actometers for 15 consecutive days in May and again in November. The data of a modified Horne and Östberg chronotype questionnaire, which were collected from 1573 female and 1124 male medical school students surveyed in the spring and autumn over an eight‐year period, were evaluated. Actiwatch® sleep analysis software was used to process the activity data with statistical analyses performed with ANOVA. We found no significant sex‐specific differences in sleep efficiency, sleep onset latency, or actual sleep‐time duration. However, we did find a difference in sleep efficiency between morning and evening types, with morning types having a higher sleep efficiency (87.9%, SD=1.3) than evening types (84.3%, SD=0.87%; p=0.007). Seasonal differences were also detected: the actual sleep‐time duration in autumn was significantly longer (mean 6.9 h, SD=0.13 h) than in spring (6.6 h, SD=0.1 h; p=0.013). Evaluation of the chronotype questionnaire data showed that individuals with no special preference for morningness or eveningness (i.e., so‐called intermediates) were most common. The distribution of chronotypes was related to the sex of subject. Men displayed eveningness significantly more often than women (28.9% males vs. 20.8% females; p<0.001), while females exhibited greater morningness (20.3% females vs.15.6% males; p<0.001). Sex influences chronotype distribution, but not actual sleep time‐duration, sleep onset latency, or sleep efficiency. The latter, however, differed among chronotypes, while actual sleep‐time duration was affected by season.     

Relation of Chronotype to Sleep Complaints in the General Finnish Population

Individuals show variation in their preference for the daily timing of activities. In this study the authors analyzed whether chronotypes associate with sleep duration and sleep-related complaints. The authors used the National FINRISK Study 2007 Survey data on 3696 women and 3162 men, representative of the Finnish population aged 25 yrs and older, for the assessment of chronotype and self-reported sleep. Evening types experienced insomnia symptoms, had nightmares, and had used recently hypnotics significantly more often than other chronotypes among both men and women. In a multinominal logistic regression model predicting insufficient sleep, the association of eveningness with insufficient sleep was not abolished after adjustment for sex, age, and sleep duration. The prevalence of short sleepers was significantly higher in evening types among men than among women, whereas that of long sleepers was significantly higher in evening types among both men and women, as compared with the other chronotypes. These results indicate that eveningness predisposes individuals to a range of sleep complaints. (Author correspondence: ilona.merikanto@helsinki.fi)     

Influence of chronotype, season, and sex of subject on sleep behavior of young adults

The aim of this study was to investigate whether sex, season, and/or chronotype influence the sleep behavior of university students. Detailed data were collected on activity/rest patterns by wrist actigraphy combined with diaries. Thirty-four medical students (19 female and 15 male) were monitored by Actiwatch actometers for 15 consecutive days in May and again in November. The data of a modified Horne and Ostberg chronotype questionnaire, which were collected from 1573 female and 1124 male medical school students surveyed in the spring and autumn over an eight-year period, were evaluated. Actiwatch sleep analysis software was used to process the activity data with statistical analyses performed with ANOVA. We found no significant sex-specific differences in sleep efficiency, sleep onset latency, or actual sleep-time duration. However, we did find a difference in sleep efficiency between morning and evening types, with morning types having a higher sleep efficiency (87.9%, SD=1.3) than evening types (84.3%, SD=0.87%; p=0.007). Seasonal differences were also detected: the actual sleep-time duration in autumn was significantly longer (mean 6.9 h, SD=0.13 h) than in spring (6.6 h, SD=0.1 h; p=0.013). Evaluation of the chronotype questionnaire data showed that individuals with no special preference for morningness or eveningness (i.e., so-called intermediates) were most common. The distribution of chronotypes was related to the sex of subject. Men displayed eveningness significantly more often than women (28.9% males vs. 20.8% females; p<0.001), while females exhibited greater morningness (20.3% females vs.15.6% males; p<0.001). Sex influences chronotype distribution, but not actual sleep time-duration, sleep onset latency, or sleep efficiency. The latter, however, differed among chronotypes, while actual sleep-time duration was affected by season.     

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)     

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.     

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 ).     

Is the shift in chronotype associated with an alteration in well-being?

The study aimed to test whether a shift in chronotype (determined by mid-sleep on free days) is associated with alterations in psychological well-being and sleep parameters. One hundred and seventeen undergraduates were tested in longitudinal study with four repeated measures. Measurements were taken during spring in three-week intervals and each measurement consisted of self-reported sleep parameters on work and free days (i.e. bedtime, sleep latency, wake time, sleep onset, mid-sleep time, social jetlag), satisfaction with life, and mood (energetic arousal, tense arousal, hedonic tone). Between-subjects analyses revealed earlier chronotypes, as compared to the later ones, showing lower tense arousal, higher energetic arousal and life satisfaction, earlier bedtime, sleep onset and offset on both work and free days, longer sleep duration and shorter sleep latency on workdays, and less social jetlag. Within-subjects analyses revealed increasing photoperiod associated with a shift toward earlier chronotype, decrease in social jetlag, and shortening sleep latency. The seasonal shift toward earlier chronotype was not associated with alterations in mood or life satisfaction, but it was associated with a shift toward earlier bedtimes and longer sleep duration on workdays, decrease in sleep latency, and social jetlag. Results from the within-subjects analyses were consistent with the results of between-subjects analyses regarding sleep–wake functioning, but inconsistent regarding psychological outcomes.     

Life between clocks: daily temporal patterns of human chronotypes

Human behavior shows large interindividual variation in temporal organization. Extreme "larks" wake up when extreme "owls" fall asleep. These chronotypes are attributed to differences in the circadian clock, and in animals, the genetic basis of similar phenotypic differences is well established. To better understand the genetic basis of temporal organization in humans, the authors developed a questionnaire to document individual sleep times, self-reported light exposure, and self-assessed chronotype, considering work and free days separately. This report summarizes the results of 500 questionnaires completed in a pilot study individual sleep times show large differences between work and free days, except for extreme early types. During the workweek, late chronotypes accumulate considerable sleep debt, for which they compensate on free days by lengthening their sleep by several hours. For all chronotypes, the amount of time spent outdoors in broad daylight significantly affects the timing of sleep: Increased self-reported light exposure advances sleep. The timing of self-selected sleep is multifactorial, including genetic disposition, sleep debt accumulated on workdays, and light exposure. Thus, accurate assessment of genetic chronotypes has to incorporate all of these parameters. The dependence of human chronotype on light, that is, on the amplitude of the light:dark signal, follows the known characteristics of circadian systems in all other experimental organisms. Our results predict that the timing of sleep has changed during industrialization and that a majority of humans are sleep deprived during the workweek. The implications are far ranging concerning learning, memory, vigilance, performance, and quality of life.     

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.     

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.     

Differential influence of asynchrony in early and late chronotypes on convergent thinking

Eveningness preference (late chronotype) was previously associated with different personality dimensions and thinking styles that were linked to creativity, suggesting that evening-type individuals tend to be more creative than the morning-types. Nevertheless, empirical data on the association between chronotype and creative performance is scarce and inconclusive. Moreover, cognitive processes related to creative thinking are influenced by other factors such as sleep and the time of testing. Therefore, our aim was to examine convergent and divergent thinking abilities in late and early chronotypes, taking into consideration the influence of asynchrony (optimal versus nonoptimal testing times) and sleep quality. We analyzed the data of 36 evening-type and 36 morning-type young, healthy adults who completed the Compound Remote Associates (CRAs) as a convergent and the Just suppose subtest of the Torrance Tests of Creative Thinking as a divergent thinking task within a time interval that did (n = 32) or did not (n = 40) overlap with their individually defined peak times. Chronotype was not directly associated with creative performance, but in case of the convergent thinking task an interaction between chronotype and asynchrony emerged. Late chronotypes who completed the test at subjectively nonoptimal times showed better performance than late chronotypes tested during their “peak” and early chronotypes tested at their peak or off-peak times. Although insomniac symptoms predicted lower scores in the convergent thinking task, the interaction between chronotype and asynchrony was independent of the effects of sleep quality or the general testing time. Divergent thinking was not predicted by chronotype, asynchrony or their interaction. Our findings indicate that asynchrony might have a beneficial influence on convergent thinking, especially in late chronotypes.     

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.     

The influences of sleep duration,chronotype, and nightwork on the ovarian cycle

ABSTRACT

Despite research indicating that sleep disorders influence reproductive health, the effects of sleep on reproductive hormone concentrations are poorly characterized. We prospectively followed 259 regularly menstruating women across one to two menstrual cycles (the BioCycle Study, 2005–2007), measuring fasting serum hormone concentrations up to eight times per cycle. Women provided information about daily sleep in diaries and chronotype and night/shift work on a baseline questionnaire. We evaluated percent differences in mean hormone concentrations, the magnitude of shifts in the timing and amplitude of hormone peaks, and the risk for sporadic anovulation associated with self-reported sleep patterns and night/shift work. We estimated chronotype scores – categorizing women below and above the interquartile range (IQR) as “morning” and “evening” chronotypes, respectively. For every hour increase in daily sleep duration, mean estradiol concentrations increased by 3.9% (95% confidence interval [CI] 2.0, 5.9%) and luteal phase progesterone by 9.4% (CI 4.0, 15.2%). Receiving less than 7 hours of sleep per day was associated with slightly earlier rises in peak levels for several hormones. Women reporting night/shift work (n = 77) had lower testosterone relative to women employed without night/shift work (percent difference: ?9.9%, CI ?18.4, ?0.4%). Women with morning chronotypes (n = 47) had earlier rises in estradiol during their cycles and potentially an earlier rise in luteinizing hormone. Compared to those who had intermediate chronotypes, women with evening chronotypes (n = 42) had a later luteinizing hormone peak of borderline statistical significance. A reduced risk for sporadic anovulation was suggested, but imprecise, for increasing hours of daily sleep leading up to ovulation (risk ratio 0.79, CI 0.59, 1.06), while an imprecise increased risk was observed for women with morning chronotypes (risk ratio 2.50, CI 0.93, 6.77). Sleep-related hormonal changes may not greatly alter ovarian function in healthy women, but have the potential to influence gynecologic health.     

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.     

The human circadian clock's seasonal adjustment is disrupted by daylight saving time

A quarter of the world's population is subjected to a 1 hr time change twice a year (daylight saving time, DST). This reflects a change in social clocks, not environmental ones (e.g., dawn). The impact of DST is poorly understood. Circadian clocks use daylight to synchronize (entrain) to the organism's environment. Entrainment is so exact that humans adjust to the east-west progression of dawn within a given time zone. In a large survey (n = 55,000), we show that the timing of sleep on free days follows the seasonal progression of dawn under standard time, but not under DST. In a second study, we analyzed the timing of sleep and activity for 8 weeks around each DST transition in 50 subjects who were chronotyped (analyzed for their individual phase of entrainment). Both parameters readily adjust to the release from DST in autumn but the timing of activity does not adjust to the DST imposition in spring, especially in late chronotypes. Our data indicate that the human circadian system does not adjust to DST and that its seasonal adaptation to the changing photoperiods is disrupted by the introduction of summer time. This disruption may extend to other aspects of seasonal biology in humans.     

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)     

Associations of chronotype with social jetlag and behavioral problems in preschool children

The timing, duration, and intensity of sleep are determined by the interaction between a sleep-wake-dependent homeostatic process and a sleep-wake-independent, intrinsic, clock-like circadian process. Chronotype represents individual differences in diurnal preferences, which are not only genetically determined but also influenced by social and environmental factors. Thus, the discrepancy between biological and social clocks, so-called “social jetlag”, occurs. Chronotype, social jetlag, and the links between chronotype and behavioral problems are well documented in adults and adolescents. However, such studies on young children are limited. We conducted a survey of sleep and health for preschool children attending kindergarten or childcare centers in Wako, Okayama and Kurashiki cities, Japan, between May and July 2012. A total of 654 children aged 4–6 years (342 boys and 312 girls, with an average age of 4.7 years) were assessed using the Children’s ChronoType Questionnaire and the Strength and Difficulties Questionnaire. Morning (M)-type, neither (N)-type and evening (E)-type accounted for 36.2%, 54.0% and 9.8% of the participants, respectively. The weekday-to-weekend differences in midsleep time – originally proposed as the concept of social jetlag – were 11, 25 and 35?min for M-, N- and E-types, respectively. There was a negative correlation between chronotype and sleep period during weekdays (p?<?0.001) and a positive correlation on weekends (p?<?0.001). The weekday-to-weekend difference in sleep period was 0.5?h for E-types, whereas there was no difference for M-types. Binomial logistic regression analyses were used to examine the links between chronotype and behavioral problems, adjusted for participants’ sex, age, childcare programs and locations. Chronotype was significantly associated with hyperactivity/inattention: N-type (adjusted OR?=?1.74, 95% CI?=?1.03–2.95, p?<?0.05) and E-type (adjusted OR?=?2.47, 95% CI?=?1.18–5.20, p?<?0.05). E-type was significantly associated with conduct problems (adjusted OR?=?2.11, 95% CI?=?1.03–4.31, p?<?0.05) and peer problems (adjusted OR?=?2.75, 95% CI?=?1.18–6.44, p?<?0.05). The results suggest that E-type children are vulnerable to higher social jetlag and more behavioral problems. The immature adjustment function of their endogenous circadian pacemakers may not be able to correct a small but significant social jetlag to synchronize with their social clocks. Furthermore, guidance based on chronobiological evidence is required for parents, teachers and health professionals to help children achieve optimal sleep and reduce behavioral problems.     

The association between sleep chronotype and obesity among black and white participants of the Bogalusa Heart Study

ABSTRACT

Research indicates that sleep duration and quality are inter-related factors that contribute to obesity, but few studies have focused on sleep chronotype, representing an individual’s circadian proclivity, nor assessed these factors in racially diverse middle-aged samples. We examined the associations between chronotype and obesity among black and white men and women participating in the Bogalusa Heart Study (BHS).

Body mass index (BMI) and sleep data were available for 1,197 middle-aged men and women (mean age 48.2 ± 5.3 years) who participated in the BHS 2013–2016. Based on the reduced Morningness-Eveningness Questionnaire’s cutoff values for chronotypes, we combined ‘definitely morning’ and ‘moderately morning’ types into ‘morning’ type, ‘definitely evening’ and ‘moderately evening’ types into ‘evening’ type and kept those who were “neither” type in a separate group. We used ‘morning’ type as the referent group. Obesity was defined as a BMI ≥ 30. Multivariable logistic regression models were used to examine associations adjusting for sex, age, education, smoking, alcohol use and drug use, depression, shift work, physical activity and sleep duration.

Evening chronotype, reported by 11.1% of participants, was associated with obesity after multi-variable adjustment, including shift work, physical activity and sleep duration (OR 1.67, 95% CI: 1.08–2.56). However, once stratified by race (black/white), this association was found only among white participants (OR = 1.91, 95% CI = 1.12–3.25) after full adjustment.

In our biracial, community-based population, evening chronotype was independently associated with obesity, specifically among white participants. Further research is needed to identify behavioral, endocrine, nutritional and genetic pathways which underlie these associations.     

Negative emotional biases in late chronotypes

Increasing evidence suggests evening chronotypes are at increased risk for developing depression. Here, we examined if, similar to acutely depressed patients, evening chronotype individuals display biases in emotional face recognition. Two hundred and twenty-six individuals completed an online survey including measures of sleep quality, depression/anxiety and chronotype followed by a simple emotion recognition task presenting male and female faces morphed in 10 steps between 0 (neutral) and 100% sad or happy. Evening chronotype was associated with increased recognition of sad facial expressions independently of sleep quality, mood, age and gender. The current results extend previous work indicating that negative biases in emotional processing are present in evening chronotypes and may have important implications for the prevention and treatment of depression in these vulnerable individuals.