Circadian preference, sleep and daytime behaviour in adolescence

Altered resting-state connectivity within default mode network associated with late chronotype

Current evidence suggests late chronotype individuals have an increased risk of developing depression. However, the underlying neural mechanisms of this association are not fully understood. Forty-six healthy, right-handed individuals free of current or previous diagnosis of depression, family history of depression or sleep disorder underwent resting-state functional Magnetic Resonance Imaging (rsFMRI). Using an Independent Component Analysis (ICA) approach, the Default Mode Network (DMN) was identified based on a well validated template. Linear effects of chronotype on DMN connectivity were tested for significance using non-parametric permutation tests (applying 5000 permutations). Sleep quality, age, gender, measures of mood and anxiety, time of scan and cortical grey matter volume were included as covariates in the regression model. A significant positive correlation between chronotype and functional connectivity within nodes of the DMN was observed, including; bilateral PCC and precuneus, such that later chronotype (participants with lower rMEQ scores) was associated with decreased connectivity within these regions. The current results appear consistent with altered DMN connectivity in depressed patients and weighted evidence towards reduced DMN connectivity in other at-risk populations which may, in part, explain the increased vulnerability for depression in late chronotype individuals. The effect may be driven by self-critical thoughts associated with late chronotype although future studies are needed to directly investigate this.

Circadian Preference, Sleep Quality, and Health-impairing Lifestyles Among Undergraduates of Medical University

Background/Aims

Health-impairing lifestyle during adolescence is an important marker for poor health. An unhealthy lifestyle may lead to physical and psychological problems in adulthood. Most of the prior researches were done among the adult population. Therefore, we assessed the chronotype pattern and correlation of health-impairing lifestyles with sleep quality according to circadian typology in medical students.

Material and Methods

In this cross-sectional research, a total of 203 subjects were enrolled. All subjects were divided into definite evening chronotype (n = 73), intermediate chronotype (n = 87), and definite morning chronotype (n = 43). Electronic media use at bedtime and duration of media use, the timing of dinner, smoking, tobacco chewing, and alcohol consumption were assessed with the help of a preformed proforma. Physical activity, sleep quality, daytime sleepiness, and chronotype were assessed by International Physical Activity Questionnaire (IPAQ), Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Score (ESS), and Morningness-Eveningness Questionnaire Self-assessment version (MEQ-SA), respectively.

Results

Subjects of the evening chronotype were suffering more with poor sleep quality. Evening chronotype had a significant (p < 0.05) positive correlation between poor sleep quality and sex, tobacco smoking, alcohol drinking, type of diet, and timing of dinner.

Conclusion

Circadian typology demonstrated the significant correlation of health-impairing lifestyles with sleep quality. From this observation, it might be a better way to plan their daily activities, in accordance with their chronotypes, benefiting not only their academic performance but also their quality of life.

Eveningness chronotype, insomnia symptoms, and emotional and behavioural problems in adolescents

OBJECTIVE

Eveningness tendency and insomnia are common in adolescents, but whether they have an independent or synergistic effect on the risk of psychopathology have remained undefined. The present study aimed to examine eveningness chronotype and insomnia symptoms in relation to mental health and emotional and behavioural problems in a community-based adolescent population.

METHODS

A total of 4948 adolescents (weighted mean age: 14.5 ± 1.8 years, weighted percentage of females: 48.9%) completed the measures. Insomnia was assessed by the Insomnia Severity Index (ISI), and chronotype preference was measured by the reduced version of the Morningness-Eveningness Questionnaire (MEQ). Emotional and behavioural problems and mental health were assessed by the Strengths and Difficulties Questionnaire (SDQ) and the General Health Questionnaire (GHQ-12), respectively. Potential confounders including demographic factors, pubertal status, general health, and sleep duration were controlled for in the analyses.

RESULTS

Insomnia symptoms were prevalent in evening-type adolescents (52% vs intermediate-type: 34.3%, morning-type: 18.0%, p < 0.001), especially two subtypes of insomnia symptoms, including difficulty initiating sleep and difficulty maintaining sleep. Eveningness and insomnia were independently associated with an increased risk of having emotional and behavioural problems (eveningness: adjusted odds ratio [AdjOR] = 1.88, 95% confidence interval [CI] = 1.61-2.19, p < 0.001; insomnia: AdjOR = 3.66, 95% CI = 2.73-4.91) as well as poor mental health in adolescents (eveningness: AdjOR = 1.25, 95% CI = 1.04-1.52, p < 0.001; insomnia: AdjOR = 3.63, 95% CI = 2.41-5.03).

CONCLUSIONS

Eveningness and insomnia symptoms are independently associated with the risk of psychopathology in adolescents. Our findings underscore the need to address both sleep and circadian factors in assessing and managing emotional and behavioural problems in the adolescent population.

Chronotype and Psychiatric Disorders

PURPOSE OF REVIEW

Chronotype, reflecting interindividual differences in daily activity patterns and sleep-wake cycles, is intrinsically connected with well-being. Research indicates increased risk of many adverse mental health outcomes for evening-type individuals. Here, we provide an overview of the current evidence available on the relationship between chronotype and psychiatric disorders.

RECENT FINDINGS

The association between eveningness and depression is well established cross-sectionally, with preliminary support from longitudinal studies. The mechanisms underlying this relationship warrant further research; deficient cognitive-emotional processes have recently been implicated. Eveningness is associated with unhealthy lifestyle habits, and the propensity of evening types to addiction has been recognized. Chronotype may also be implicated in disordered eating.

SUMMARY

Eveningness is associated with depression-including seasonal affective disorder (SAD)-and substance dependence, while support for a relation with anxiety disorders and psychosis is lacking. In bipolar disorder, chronotype is linked to depression but not mania. Eveningness is also related to sleep disturbances and poor lifestyle habits, which may increase risk for psychiatric disorders.

Course, risk factors, and mental health outcomes of excessive daytime sleepiness in rural Chinese adolescents: A one-year prospective study

BACKGROUND

This study aimed to examine the one-year incidence and persistence of excessive daytime sleepiness (EDS) in rural Chinese adolescents and their risk factors. In addition, we also aimed to explore the potential bidirectional associations of EDS with anxiety symptoms and depressive symptoms.

METHODS

A total of 3736 adolescents from 5 high schools from rural area in the south China were eligible for follow-up. Among them, 2787 responded to follow-up after one year. EDS was defined as having a total score of the Epworth Sleepiness Scale over 10.

RESULTS

The one-year persistence rate and incidence rate of EDS were 27.6% and 9.3%, respectively. After controlling for age and sex, new incident EDS was significantly associated with perceived high study stress, depressive symptoms, insomnia symptoms, and high life events at baseline. Baseline EDS predicted new onsets of depression and anxiety at follow-up. Cross-lagged analyses further revealed that there were bidirectional associations between EDS and anxiety symptom and between EDS and depressive symptoms. Persistent EDS was only associated with eveningness chronotype. In particular, short sleep duration and obesity were associated with neither new incidence nor persistence of EDS in this population.

LIMITATIONS

All measures relied on self-reported questionnaires rather than objective assessments, which might have led to report bias.

CONCLUSIONS

We have identified a number of risk factors of the one-year incidence of EDS (such as perceived high study stress, depressive symptoms, insomnia symptoms, and high life events) and persistence of EDS (eveningness chronotype) in rural adolescents. There is a reciprocal relationship of EDS with anxiety and depression. In this population, sleep loss and obesity seem not related to the course of EDS.

Chronotype and response to training during the polar night: a pilot study

BACKGROUND

An individual's chronotype influences his or her physiological rhythms. Some studies have looked at the effect of time of day on the responses to exercise, but studies on the effect of long-term training are lacking.

OBJECTIVE

To report the effects of an 8-week training period during the polar night in non-athletes of different chronotypes living at 70°N.

DESIGN

In all, 10 morning (M), 10 neither (N) and 10 evening (E) types were recruited, and their aerobic capacity (VO_2max), strength, flexibility and balance before and after the training period were tested.

RESULTS

3 E-types, 5 N-types and 6 M-types completed the protocol. An increase in VO_2max and strength was observed for the whole group. The best negative correlation (r=-0.5287) was found between the Morningness-Eveningness Questionnaire (MEQ) score and the increase in VO2max, and the best positive correlation (r=0.4395) was found between MEQ and the increase in strength. Changes in balance and flexibility did not show any clear trends.

CONCLUSION

In an environment with no outdoor daylight, it seems that the response to 8 weeks of aerobic training is larger in the E- than in the M-types, although the M-types showed a larger improvement in strength.

Free-running circadian period in adolescents and adults

Sleep timing shifts later during adolescence (second decade). This trend reverses at ~20 years and continues to shift earlier into adulthood. The current analysis examined the hypothesis that a longer free-running circadian period during late adolescence (14-17 years) compared with adulthood (30-45 years) accounts for sleep timing differences. Sex and ancestry were also examined because previous reports find that women and those with African-American ancestry have shorter free-running periods. Circadian period was measured using an ultradian dark-light protocol (2 hr dark/sleep, 2 hr dim room light [~20 lux]/wake) over 3.4 days. Dim light melatonin onsets were measured before and after the ultradian protocol, from which the circadian period was derived. In contrast to our hypothesis, we found that free-running circadian period was similar in adolescents and adults. African-American adults had shorter free-running circadian periods compared with adults of other ancestries. This ancestry difference was not seen in the adolescent group. Finally, we observed a non-significant trend for shorter free-running circadian periods in females compared with males. These data suggest that age-related changes in circadian period after late adolescence do not account for sleep timing differences. These data provide further support for ancestry-related differences in period, particularly in adults. Whether the large difference in circadian period between African-American and other ancestries emerges later in development should be explored.

Persistence of social jetlag and sleep disruption in healthy young adults

Sleep disruption has been associated with increased risks for several major chronic diseases that develop over decades. Differences in sleep/wake timing between work and free days can result in the development of social jetlag (SJL), a chronic misalignment between a person's preferred sleep/wake schedule and sleep/wake timing imposed by his/her work schedule. Only a few studies have examined the persistence of SJL or sleep disruption over time. This prospective investigation examined SJL and sleep characteristics over a 2-year period to evaluate whether SJL or poor sleep were chronic conditions during the study period. SJL and sleep measures (total sleep time [TST], sleep onset latency [SOL], wake after sleep onset [WASO]), and sleep efficiency [SE]), were derived from armband monitoring among 390 healthy men and women 21-35 years old. Participants wore the armband for periods of 4-10 days at 6-month intervals during the follow-up period (N = 1431 repeated observations). The consistency of SJL or sleep disruption over time was analyzed using generalized linear mixed models (GLMMs) for repeated measures. Repeated measures latent class analysis (RMLCA) was then used to identify subgroups among the study participants with different sleep trajectories over time. Individuals in each latent group were compared using GLMMs to identify personal characteristics that differed among the latent groups. Minor changes in mean SJL, chronotype, or TST were observed over time, whereas no statistically significant changes in SOL, WASO, or SE were observed during the study period. The RMLCA identified two groups of SJL that remained consistent throughout the study (low SJL, mean ± SE: 0.4 ± 0.04 h, 42% of the study population; and high SJL, 1.4 ± 0.03 h, 58%). Those in the SJL group with higher values tended to be employed and have an evening chronotype. Similarly, two distinct subgroups were observed for SOL, WASO, and SE; one group with a pattern suggesting disrupted sleep over time, and another with a consistently normal sleep pattern. Analyses of TST identified three latent groups with relatively short (5.6 ± 1.0 h, 21%), intermediate (6.5 ± 1.0 h, 44%), and long (7.3 ± 1.0 h, 36%) sleep durations, all with temporally stable, linear trajectories. The results from this study suggest that sleep disturbances among young adults can persist over a 2 year period. Latent groups with poor sleep tended to be male, African American, lower income, and have an evening chronotype relative to those with more normal sleep characteristics. Characterizing the persistence of sleep disruption over time and its contributing factors could be important for understanding the role of poor sleep as a chronic disease risk factor.

Effects of sleep on substance use in adolescents: a longitudinal perspective

Substance use (SU) and sleep problems appear interrelated, but few studies have examined the influence of adolescent sleep patterns on development of SU disorders. This study prospectively examined the influence of sleep habits on subsequent SU in youth who later transitioned into heavy drinking. At time 1 (T1), participants (n = 95) were substance-naive 12- to 14-year-olds. Path-analytic models examined whether the effects of T1 risk factors (familial SU disorder, inhibition control, and externalizing and internalizing traits) on time 3 (M = 19.8 years old) tobacco, alcohol, and cannabis were mediated by time 2 (M = 15.1 years old) sleep chronotype, daytime sleepiness, and erratic sleep/wake behaviors. Significant direct path effects of T1 risk factors and time 2 sleep behaviors on time 3 SU were found, Ps < 0.05. In models that examined the effect of each individual sleep behavior separately on SU, more erratic sleep/wake and greater daytime sleepiness predicted higher lifetime use events for all substances (Ps < 0.01). Higher evening chronotype tendencies predicted lower tobacco and higher alcohol and cannabis lifetime use events (Ps < 0.01). Erratic sleep/wake behaviors mediated the effect of inhibitory control on subsequent SU; less erratic sleep/wake behaviors predicted better inhibition control ( β̂= -0.20, P < 0.05). Early-mid adolescent psychiatric health and sleep behaviors prior to drinking onset predicted greater SU 5 years later. Participants were substance-naïve at baseline, allowing for the examination of temporal order in the relationship between sleep problems and alcohol use. Early adolescent sleep problems may be an important risk factor for SU in later life.

Evening use of caffeine moderates the relationship between caffeine consumption and subjective sleep quality in students

Caffeine is often used to reduce sleepiness; however, research suggests that it can also cause poor sleep quality. The timing of caffeine use, amongst other factors, is likely to be important for the effects it has on sleep quality. In addition, individual differences exist in the effect of caffeine on sleep quality. This cross-sectional study investigated the influence of the timing of caffeine consumption on and a possible moderating role of chronotype in the relationship between caffeine consumption and sleep quality in 880 students (74.9% female, mean age 21.3 years, SD = 3.1). Respondents filled in online questionnaires about chronotype (the Morningness-Eveningness Questionnaire), sleep quality (the Pittsburgh Sleep Quality Index) and caffeine consumption. Mean caffeine consumption was 624 mg per week, and 80.2% of the sample drank caffeine after 18:00 hours. Regression analyses demonstrated that higher total caffeine consumption was only related to poorer sleep quality for people who did not drink caffeine in the evening (β = 0.209, p = .006). We did not find a relationship between caffeine and sleep quality in people who drank caffeine in the evening (β = -0.053, p = .160). Furthermore, we found no evidence for a moderating role of chronotype in the relationship between caffeine consumption and sleep quality. We concluded that a self-regulating mechanism is likely to play a role, suggesting that students who know that caffeine negatively affects their sleep quality do not drink it in the evening. Caffeine sensitivity and the speed of caffeine metabolism may be confounding variables in our study.

A randomised controlled trial of bright light therapy and morning activity for adolescents and young adults with Delayed Sleep-Wake Phase Disorder

A randomised controlled trial evaluated bright light therapy and morning activity for the treatment of Delayed Sleep-Wake Phase Disorder (DSWPD) in young people. 60 adolescents and young adults (range = 13-24 years, mean = 15.9 ± 2.2 y, 63% f) diagnosed with DSWPD were randomised to receive three weeks of post-awakening Green Bright Light Therapy (∼507 nm) and Sedentary Activity (sitting, watching TV), Green Bright Light Therapy and Morning Activity (standing, playing motion-sensing videogame), Red Light Therapy (∼643 nm) and Sedentary Activity or Red Light Therapy and Morning Activity. Sleep (ie sleep onset time, wake up time, sleep onset latency, total sleep time) and daytime functioning (ie morning alertness, daytime sleepiness, fatigue, functional impairment) were measured pre-treatment, post-treatment and at one and three month follow-up. Contrary to predictions, there were no significant differences in outcomes between treatment groups; and interaction effects between treatment group and time for all outcome variables were not statistically significant. However, adolescents and young adults in morning activity conditions did not meaningfully increase their objective activity (ie movement frequency). Overall, adolescents reported significantly improved sleep timing (d = 0.30-0.46), sleep onset latency (d = 0.32) and daytime functioning (d = 0.45-0.87) post-treatment. Improvements in sleep timing (d = 0.53-0.61), sleep onset latency (d = 0.57), total sleep time (d = 0.51), and daytime functioning (d = 0.52-1.02) were maintained, or improved upon, at the three month follow-up. However, relapse of symptomology was common and 38% of adolescents and young adults requested further treatment in addition to the three weeks of light therapy. Although there is convincing evidence for the short-term efficacy of chronobiological treatments for DSWPD, long-term treatment outcomes can be improved. To address this gap in our current knowledge, avenues for future research are discussed.

CLINICAL TRIAL

Australian & New Zealand Clinical Trials Registry, https://www.anzctr.org.au, ACTRN12614000308695.

Sleep, Circadian Rhythms, and Risk Across Health Domains in Adolescents With an Evening Circadian Preference

Sleep and circadian rhythm changes during adolescence contribute to increased risk across emotional, behavioral, cognitive, social, and physical health domains. This study examines if sleep and dim light melatonin onset (DLMO) are related to greater risk in these 5 health domains. Participants were 163 (93 female, age = 14.7 years) adolescents with an evening circadian preference from a study funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Sleep and circadian measures included weekday total sleep time (TST), bedtime, and shut-eye time assessed via sleep diary, the Children's Morningness-Eveningness Preferences scale, and DLMO. Health domains included self-reported emotional, cognitive, behavioral, social, and physical health. Later DLMO was significantly associated with shorter weekday TST, later weekday bedtime, and later weekday shut-eye time, as well as lower risk in the behavioral domain. At the trend level, later DLMO was related to fewer physical health problems. Earlier DLMO combined with a later bedtime, later shut-eye time, or shorter TST predicted greater risk in the cognitive domain. Later DLMO and shorter TST or a later bedtime predicted worse physical health. DLMO timing was not related to the emotional or social domain. There is evidence that a discrepancy between sleep behaviors and the endogenous circadian rhythm may be related to risk in the cognitive domain for adolescents with an evening circadian preference. Preliminary evidence also indicated that a delayed DLMO and shorter TST or a later bedtime may be related to vulnerability to physical health risk.

Changes in growth and sleep across school nights, weekends and a winter holiday period in two Australian schools

Studies suggest that there may be an association between sleep and growth; however, the relationship is not well understood. Changes in biology and external factors such as school schedule heavily impact the sleep of adolescents, during a critical phase for growth. This study assessed the changes in sleep across school days, weekends and school holidays, while also measuring height and weight changes, and self-reported alterations in food intake and physical activity. The impact of morningness-eveningness (M-E) on height change and weight gain was also investigated. In a sample of 63 adolescents (mean age = 13.13, SD = 0.33, 31 males) from two independent schools in South Australia, height and weight were measured weekly for 4 weeks prior to the school holidays and 4 weeks after the school holidays. Participants also completed a Morningness/Eveningness Scale and 7-day sleep, diet and physical activity diaries prior to, during and after the school holidays. Participants at one school had earlier wake times during the weekends than participants attending the other school, leading to a significantly shorter sleep duration on weekends for those participants. Regardless of school, sleep was significantly later and longer during the holidays (p < 0.001) and those with a stronger morning preference fell asleep (F_18,36 = 3.4, p = 0.001) and woke (F_18,44 = 2.0, p = 0.027) earlier than evening types. Growth rate was lower during the holiday weeks. For those attending the school with limited sleep in opportunities, growth after the holidays was lower for those with greater evening preference, whereas for those at the other school, growth was greater for those with greater evening preference. The increase in average weight from pre- to post-holidays was greater for those attending the school with limited opportunities to sleep longer. Participants reported greater food intake during the holidays compared to school days and greater physical activity levels on weekends compared to school days, and school days compared to holidays. Results suggest that time of day preference may impact growth, with evening types who cannot sleep in growing at a slower rate than evening types who can or morning types. This may be related to sleep restriction. Despite sleep being both later and longer during the school holidays, participants' growth slowed during the holiday period. It is possible that this may be a reflection of other behavioural changes in the holidays (increased food intake and reduced physical activity), as sleep timing during the school period was related to growth.

Nocturnal sleep mediates the relationship between morningness-eveningness preference and the sleep architecture of afternoon naps in university students

The present study investigated the parameters of nocturnal sleep that mediate the relationship between morningness-eveningness preference and the sleep architecture of naps in university students. This study had a cross-sectional, descriptive correlational design. The sleep architecture of 52 students invited to take an afternoon nap in the laboratory was recorded. The morningness-eveningness questionnaire (MEQ) was used to evaluate morningness-eveningness preference. An actigraph was used to collect students' nighttime sleep data in the week preceding the study. Polysomnography was used to measure the sleep architecture of the participants' naps. After adjustments for potential factors, although the MEQ did not directly correlate with the percentage of sleep stages in naps, the effects of the MEQ on the percentage of Stage 1 sleep, slow-wave sleep, and rapid eye movement sleep; sleep duration; and sleep efficiency of naps were mediated by the total sleep time in the preceding week. This preliminary study suggests that nap quality was affected by morningness-eveningness preference through the mediation of total nocturnal sleep time. Therefore, future studies should be carefully designed to consider nighttime sleep patterns when analyzing the effects of chronotypes on daytime sleep.

Time to learn: How chronotype impacts education

A growing body of literature has linked chronotype and sleep to school performance. Chronotype is under the control of the circadian clock and refers to sleep timing and diurnal preferences. Chronotype changes with age and is latest during adolescence, giving rise to a mismatch between the (late) circadian clock and the (early) school clock. In general, evening (late) chronotypes obtain lower grades. School performance is influenced by many other factors, such as motivation, intelligence, and conscientiousness. Some of these factors also relate to chronotype. The present paper reviews the literature on the relationship between chronotype and school performance, with the aim of suggesting hypotheses about the mechanisms behind this complex phenomenon and exploring solutions for an optimized school system. Based on the literature reviewed, we hypothesize that chronotype has both a direct and an indirect effect on school performance. The indirect effect is mediated by factors such as conscientiousness, learning/achieving motivation, mood, and alertness. In addition, time of day of testing plays an important role since the chronotype effect on grades is strongest in the morning and disappears in the afternoon. Strategies to decrease the mismatch between the adolescent circadian clock and the school clock could involve light interventions to advance the students' sleep timing, delays in school starting times, and rearrangements of test schedules (tests later in the day).

The relationship between depression and chronotype: A longitudinal assessment during childhood and adolescence

BACKGROUND/OBJECTIVE

During adolescence, chronotype shifts toward "eveningness." "Eveningness" is related to negative physical and mental health outcomes. Little is known about what influences the shift in chronotype beyond pubertal status. The current study examined the influence of earlier depression predicting later individual differences in adolescent chronotype, accounting for pubertal status, and the prospective prediction of later increases in depression from earlier chronotype.

METHODS

Youth (age M = 12.06, SD = 2.35; 56.5% girls) from the community completed repeated assessments of depression, including both self-reports (14 assessments) and diagnostic interviews (eight assessments), over a 48-month period. At the 36-month timepoint, participants completed chronotype and pubertal development measures. Regression and ANOVA analyses examined: (1) the influence of earlier depression levels (baseline to 36 months) upon chronotype, and (2) chronotype (at 36 months) upon later depression (48 months).

RESULTS

Youth with higher earlier depression symptoms (β = -0.347, P < .001) and history of depression diagnosis (β = -0.13, P = .045) showed a greater eveningness preference controlling for pubertal status, age, and gender. Further, depression diagnosis history interacted with pubertal status to predict chronotype: (F(1,243) = 4.171, P = .045) such that the influence of depression on chronotype was greatest among postpubertal youth (t = 3.271, P = .002). Chronotype (greater eveningness preference) predicted prospective increases in depression symptoms (β = -0.16, P = .03) and onset of depressive episode (b = -0.085, OR = 0.92, P = .03) 1 year later.

CONCLUSION

Depression, experienced earlier in life, predicts greater preference for eveningness, especially among postpubertal youth. In turn, later depression is predicted by evening preference. These findings suggest the reciprocal interplay between mood and biological rhythms, especially depression and chronotype, during adolescence.

Chronotype Differences in Health Behaviors and Health-Related Quality of Life: A Population-Based Study Among Aged and Older Adults

This study investigates health behaviors, health-related quality of life (HRQOL) and sleep among chronotypes in a community-based sample (n = 2,976). Analysis of covariance indicated evening types (E-types) had a significantly higher percentage of current smokers and more sleep-interfering behaviors compared to intermediate and morning types (M-type), and also lower physical activity and more sleep disturbance compared to M-types. E-types also had worse mental HRQOL compared to both chronotypes, and worse physical HRQOL compared to M-types. Exploratory analyses indicated E-types consumed more caffeinated beverages at night, smoked or ate heavy meals before bedtime, kept irregular sleep-wake schedules, and took more naps. Mediational analyses indicated that sleep-interfering behavior partially mediated the relationship between chronotype and sleep disturbance, and physical activity partially mediated the relationship between chronotype and mental HRQOL. E-types had more unhealthy behaviors, which may subsequently place them at higher risk for health problems.

Human Adolescent Phase Response Curves to Bright White Light

Older adolescents are particularly vulnerable to circadian misalignment and sleep restriction, primarily due to early school start times. Light can shift the circadian system and could help attenuate circadian misalignment; however, a phase response curve (PRC) to determine the optimal time for receiving light and avoiding light is not available for adolescents. We constructed light PRCs for late pubertal to postpubertal adolescents aged 14 to 17 years. Participants completed 2 counterbalanced 5-day laboratory sessions after 8 or 9 days of scheduled sleep at home. Each session included phase assessments to measure the dim light melatonin onset (DLMO) before and after 3 days of free-running through an ultradian light-dark (wake-sleep) cycle (2 h dim [~20 lux] light, 2 h dark). In one session, intermittent bright white light (~5000 lux; four 20-min exposures) was alternated with 10 min of dim room light once per day for 3 consecutive days. The time of light varied among participants to cover the 24-h day. For each individual, the phase shift to bright light was corrected for the free-run derived from the other laboratory session with no bright light. One PRC showed phase shifts in response to light start time relative to the DLMO and another relative to home sleep. Phase delay shifts occurred around the hours corresponding to home bedtime. Phase advances occurred during the hours surrounding wake time and later in the afternoon. The transition from delays to advances occurred at the midpoint of home sleep. The adolescent PRCs presented here provide a valuable tool to time bright light in adolescents.

Chronotype preference matters for depression in youth

Morningness/eveningness (M/E) preference is an important circadian rhythm indicator with strong individual variation. M/E chronotype has been found to be correlated with depression in adults, yet the relationship is less clear in children and adolescents. Additionally, poor sleep quality is another commonly studied risk factor for depression. The aims of the present study are to investigate the independent effects of M/E chronotype on youth depression using both self-report and parental-report questionnaires. We also evaluated how poor sleep quality may affect the relationship through a mediating or moderating effect. In total, 2,139 students attending grades 1 to 7 participated in this study. They completed questionnaires regarding M/E chronotype, depression, and sleep quality. A total of 1,708 parents also participated and filled out parental-reports of emotional and behavioral problems of their children. The prevalence of self- and parental-report depression was 16.8% and 12.8% among young students, respectively. Overall, 15.4% of the students were the eveningness type. Being an eveningness type was independently associated with self-report depression after adjustment for poor sleep quality (OR = 1.86, 95% CI = 1.07-3.24). We also observed that poor sleep quality mediated the influence of M/E chronotype on self-report depression among students aged 7-13 years (p < 0.001). On the other hand, being an eveningness type was associated with a number of parental-report emotional and behavioral problems in the students, in addition to depression, although these associations become non-significant after adjusted for poor sleep quality. Our results demonstrate the importance of M/E chronotype on youth depression and poor sleep quality partly mediates this effect.

Associations among daytime sleepiness, depression and suicidal ideation in Korean adolescents

The aim of this study was to examine the effects of daytime sleepiness on depression and suicidal ideation in adolescent high-school students. A survey of 538 high school students aged 16-17 years attending two academic schools was conducted. The Epworth Sleepiness Scale (ESS), the Beck Depression Inventory and the Scale for Suicide Ideation were used to assess subjects' daytime sleepiness, depression and suicidal ideation. The mean score for daytime sleepiness was 8.52, which indicates a sleep deficit. Significant positive correlations were found between daytime sleepiness and depression, between daytime sleepiness and suicidal ideation and between depression and suicidal ideation. Gender and depression were significant predictors of suicidal ideation, accounting for 48% of the variance in this measure. Depression acts as a mediator of the relationship between daytime sleepiness and suicidal ideation. High school students in Korea generally have insufficient sleep time and feel sleepy during the day; insufficient sleep during adolescence may be associated with depression and suicidal ideation.

Sleep timing is associated with self-reported dietary patterns in 9- to 15-year-olds

OBJECTIVE

To examine sleep timing differences in self-reported dietary patterns of children and adolescents.

DESIGN

Cross-sectional.

PARTICIPANTS

Students aged 9-15 years (n=119, 11.7±1.3 years, 76% female) attending a summer program for the gifted. The upper and lower quartiles of reported midsleep time (weighted weekday-weekend average) were used to identify early (n=28) and late (n=27) sleep timing groups.

METHODS

Sleep patterns were assessed via self-report. Participants also rated their likelihood to consume 9 different categories of food and drinks on a 5-point scale ranging from "no likelihood" to "high likelihood." Foods were grouped as follows: (1) sugary and caffeinated beverages; (2) high-energy-dense, nutrient-poor foods (ie, sugary, salty, fatty foods); and (3) low-energy-dense, nutrient-rich foods (ie, vegetables, proteins, carbohydrates, fruits).

RESULTS

Midsleep time was 02:11±00:25 for the early and 06:14±01:00 for the late sleep timing groups. Participants reporting later sleep timing were more likely to consume sugary/caffeinated beverages and high-energy-dense, nutrient-poor foods throughout the day compared with their early sleep timing peers. The late vs the early sleep timing group also had a higher likelihood of overall consumption of foods and drinks from all categories into the evening and nighttime hours.

CONCLUSION

Our findings indicate that children and adolescents who exhibit late sleep timing are more likely to make poorer dietary choices, which may have important implications for understanding pathways to adiposity and obesity risk during this sensitive period of development.

An approach to understanding sleep and depressed mood in adolescents: person-centred sleep classification

Depressive mood in youth has been associated with distinct sleep dimensions, such as timing, duration and quality. To identify discrete sleep phenotypes, we applied person-centred analysis (latent class mixture models) based on self-reported sleep patterns and quality, and examined associations between phenotypes and mood in high-school seniors. Students (n = 1451; mean age = 18.4 ± 0.3 years; 648 M) completed a survey near the end of high-school. Indicators used for classification included school night bed- and rise-times, differences between non-school night and school night bed- and rise-times, sleep-onset latency, number of awakenings, naps, and sleep quality and disturbance. Mood was measured using the total score on the Center for Epidemiologic Studies-Depression Scale. One-way anova tested differences between phenotype for mood. Fit indexes were split between 3-, 4- and 5-phenotype solutions. For all solutions, between phenotype differences were shown for all indicators: bedtime showed the largest difference; thus, classes were labelled from earliest to latest bedtime as 'A' (n = 751), 'B' (n = 428) and 'C' (n = 272) in the 3-class solution. Class B showed the lowest sleep disturbances and remained stable, whereas classes C and A each split in the 4- and 5-class solutions, respectively. Associations with mood were consistent, albeit small, with class B showing the lowest scores. Person-centred analysis identified sleep phenotypes that differed in mood, such that those with the fewest depressive symptoms had moderate sleep timing, shorter sleep-onset latencies and fewer arousals. Sleep characteristics in these groups may add to our understanding of how sleep and depressed mood associate in teens.

Life Threat and Sleep Disturbances in Adolescents: A Two-Year Follow-Up of Survivors From the 2011 Utøya, Norway, Terror Attack

A significant number of adolescents have been exposed to traumatic life events. However, knowledge about the specific sleep disturbance that occurs in individuals after trauma exposure is predominantly based on studies of adults. This study reports specific sleep disturbance in 42 survivors of the 2011 mass shooting at a youth summer camp on the Norwegian island Utøya, mean age = 20.91 years, SD = 2.32, 62.5% females. When compared with matched controls, significantly more survivors reported having sleep disturbances, 52.4% versus 13.6%, d = 0.93, of which onset began at the time of the shooting, χ² = 14.9, p < .001. The prevalence of insomnia, 56.3% versus 11.0%, d = 0.73; excessive daytime sleepiness, 34.4% versus 13.6%, d = 0.61; symptoms of obstructive sleep apnea, 18.8% versus 0%, d = 0.70; and frequent nightmares, 37.5% versus 2.3%, d = 0.90, were all higher in the survivors than in the controls. In a subgroup of survivors (n = 20) with psychiatric diagnoses, sleep disturbances were more prevalent than in survivors without psychiatric diagnosis. Actigraphy data revealed delayed bedtime, sleep onset, and rise time in survivors compared with controls, ts > 1.7, ps = .044 to .028. These results corroborate the effects of a life threat on the range and extent of sleep disturbances, and emphasize the need to better assess and treat sleep disorders in adolescents exposed to trauma.

Eveningness and Later Sleep Timing Are Associated with Greater Risk for Alcohol and Marijuana Use in Adolescence: Initial Findings from the National Consortium on Alcohol and Neurodevelopment in Adolescence Study

BACKGROUND

Abundant cross-sectional evidence links eveningness (a preference for later sleep-wake timing) and increased alcohol and drug use among adolescents and young adults. However, longitudinal studies are needed to examine whether eveningness is a risk factor for subsequent alcohol and drug use, particularly during adolescence, which is marked by parallel peaks in eveningness and risk for the onset of alcohol use disorders. This study examined whether eveningness and other sleep characteristics were associated with concurrent or subsequent substance involvement in a longitudinal study of adolescents.

METHODS

Participants were 729 adolescents (368 females; age 12 to 21 years) in the National Consortium on Alcohol and Neurodevelopment in Adolescence study. Associations between the sleep variables (circadian preference, sleep quality, daytime sleepiness, sleep timing, and sleep duration) and 3 categorical substance variables (at-risk alcohol use, alcohol bingeing, and past-year marijuana use [y/n]) were examined using ordinal and logistic regression with baseline age, sex, race, ethnicity, socioeconomic status, and psychiatric problems as covariates.

RESULTS

At baseline, greater eveningness was associated with greater at-risk alcohol use, greater bingeing, and past-year use of marijuana. Later weekday and weekend bedtimes, but not weekday or weekend sleep duration, showed similar associations across the 3 substance outcomes at baseline. Greater baseline eveningness was also prospectively associated with greater bingeing and past-year use of marijuana at the 1-year follow-up, after covarying for baseline bingeing and marijuana use. Later baseline weekday and weekend bedtimes, and shorter baseline weekday sleep duration, were similarly associated with greater bingeing and past-year use of marijuana at the 1-year follow-up after covarying for baseline values.

CONCLUSIONS

Findings suggest that eveningness and sleep timing may be under recognized risk factors and future areas of intervention for adolescent involvement in alcohol and marijuana that should be considered along with other previously identified sleep factors such as insomnia and insufficient sleep.

The Impact of Sleep Improvement on Food Choices in Adolescents With Late Bedtimes

PURPOSE

The aim was to investigate the effect of sleep improvement on desire for and intake of weight gain-promoting foods in adolescents with late bedtimes.

METHODS

A sample of 42 adolescents with late bedtimes was enrolled in an intervention designed to improve sleep. Their desire for and intake of food in the morning was assessed at before and after treatment.

RESULTS

Adolescents with earlier bedtimes at post-treatment relative to pretreatment increased their caloric intake of low glycemic index, fruit, and dairy foods at post-treatment. This effect was not observed in adolescents who did not improve their bedtime at post-treatment.

CONCLUSIONS

These findings suggest that advancing bedtimes earlier can improve breakfast choices, an important meal for obesity prevention during adolescence.

Differential effects of circadian typology on sleep-related symptoms, physical fatigue and psychological well-being in relation to resilience

Various physiological and psychological functions are influenced by circadian typology (CT), which was reported to be related to resilience. However, few studies have assessed the effects of CT in relation to resilience. The aim of the present study was to assess the influence of CT on sleep-related symptoms, physical fatigue and psychological well-being in relation to resilience. The present study included a total of 1794 healthy hospital employees, and they completed the Morningness-Eveningness Questionnaire, Connor-Davidson Resilience Scale, Pittsburgh Sleep Quality Index, Epworth Sleepiness Scale, Fatigue Severity Scale, Hospital Anxiety and Depression Scale and World Health Organization Quality of Life Scale Abbreviated Version. Subjects with evening type showed lower sleep quality, more daytime sleepiness and physical fatigue than neither types and morning types. Additionally, evening types were more depressed and anxious and reported a poorer quality of life. CT was found to be a significant predictor of sleep quality, but CT was minimally associated with physical fatigue and psychological well-being in the regression analysis. Instead, resilience was substantially related to all of the variables measured. In conclusion, CT independently predicts sleep quality, but the effects of CT on physical fatigue and psychological well-being are negligible compared to those of resilience.

From Lark to Owl: developmental changes in morningness-eveningness from new-borns to early adulthood

Morningness-eveningness or chronotype changes significantly throughout the life span. This has been reported for the transition during adolescence in some studies, and to a lesser extent in early adulthood. Primary and pre-school children have been under investigation in fewer studies. This is the first comprehensive study covering the age range from very young children until early adulthood (0-30 years) based on the same measurement instrument. Here, we show that the turn towards eveningness starts at an early age in German children. Based on 26,214 cross-sectional data, we further show that at the end of adolescence, morningness-eveningness does not significantly change during early adulthood. Sex differences arise during puberty and remain until 30 years. The breaking point for the turn towards morningness is 15.7 years in girls and 17.2 boys. At the age of 0-1 years, there are about 70% morning types, and about 1% evening types, while at the age of 16 years, only 5% are morning types and 19% are evening types.

Sleep quality perception and romantic relationships in university students: cross-sectional study

Introducción. El sueño en adolescentes está influenciado de manera especial por los estados emocionales presentes en las relaciones románticas. Esto puede ser determinante en la percepción de calidad del sueño.Objetivo. Evaluar la asociación entre la percepción de la calidad del sueño y las características de las relaciones románticas en estudiantes universitarios adolescentes y adultos jóvenes.Materiales y métodos. Estudio de corte transversal realizado en 443 sujetos. La percepción de calidad del sueño, los estilos de apego, estar en una relación romántica y sus características se determinaron utilizando medidas validadas.Resultados. La percepción de calidad del sueño se determinó utilizando cinco modelos multivariados que incluyeron características estadísticamente significativas de las relaciones románticas. El nivel de satisfacción del individuo con su relación de pareja y la atracción hacia esta se asoció con su nivel de percepción de calidad del sueño (p=0.035). La prevalencia de las relaciones románticas fue del 64% (IC95%: 59.4-68.9). Los que no estaban en una relación experimentaron latencia del sueño significativamente más prolongada (p<0.05).Conclusión. Las relaciones sentimentales románticas y sus características se asocian con la calidad de sueño percibida por los individuos. Estos aspectos pueden ser identificados e intervenidos y ser útiles para los sistemas de apoyo de las instituciones educativas.

Eveningness among late adolescent males predicts neural reactivity to reward and alcohol dependence 2 years later

Eveningness, a preference for later sleep-wake timing, is linked to altered reward function, which may explain a consistent association with substance abuse. Notably, the extant literature rests largely on cross-sectional data, yet both eveningness and reward function show developmental changes. We examined whether circadian preference during late adolescence predicted the neural response to reward 2 years later. A sample of 93 males reported circadian preference and completed a monetary reward fMRI paradigm at ages 20 and 22. Primary analyses examined longitudinal paths from circadian preference to medial prefrontal cortex (mPFC) and ventral striatal (VS) reward responses. We also explored whether reward responses mediated longitudinal associations between circadian preference and alcohol dependence, frequency of alcohol use, and/or frequency of cannabis use. Age 20 eveningness was positively associated with age 22 mPFC and VS responses to win, but not associated with age 22 reactivity to reward anticipation. Age 20 eveningness was indirectly related to age 22 alcohol dependence via age 22 mPFC response to win. Our findings provide novel evidence that altered reward-related brain function could underlie associations between eveningness and alcohol use problems. Eveningness may be an under-recognized but modifiable risk factor for reward-related problems such as mood and substance use disorders.

Prevalence of sleep bruxism and awake bruxism in different chronotype profiles: Hypothesis of an association

Sleep (SB) and awake bruxism (AB) recognize a multifactorial etiology and have a relationship with several psychological factors. Psychological disorders have recently been associated also with the chronotype, which is the propensity for an individual to be especially active at a particular time during a 24-h period. Based on the chronotype, the two extreme profiles are morningness and eveningness individuals. Due to the relationship that both the chronotype and bruxism have with psychological factors and the fact that performing tasks not compatible with chronotype can trigger stress, this review presents the hypothesis that the prevalence of SB and AB can differ with the various chronotype profiles. New perspectives for the study of bruxism etiology may emerge from investigations on the topic.

Associations of Caffeinated Beverage Consumption and Screen Time with Excessive Daytime Sleepiness in Korean High School Students

The present study investigated caffeinated beverage consumption and screen time in the association with excessive daytime sleepiness (EDS) and sleep duration. We conducted a cross-sectional study including 249 Korean male high school students. These participants responded to a questionnaire inquiring the information on lifestyle factors, consumption of caffeinated beverages, time spent for screen media, and sleep duration as well as to the Epworth Sleepiness Scale (ESS) questionnaire. EDS was defined as ESS scores of 9 or greater. Students with EDS consumed greater amount of chocolate/cocoa drinks and spent longer time for a TV and a mobile phone than those without EDS (p < 0.05). In addition, students with short sleep (≤ 6 hours) consumed greater amount of coffee than others whereas students with long sleep (> 8 hours) consumed greater amount of chocolate/cocoa drinks than others (p < 0.05). Screen time did not differ according to the categories of sleep duration. Although these findings do not support causal relationships, they suggest that screen time is associated with EDS, but not with sleep duration, and that consumption of certain types of caffeinated beverages is associated with EDS and sleep duration. Adolescents may need to reduce screen time and caffeine consumption to improve sleep quality and avoid daytime sleepiness.

Sleep and optimism: A longitudinal study of bidirectional causal relationship and its mediating and moderating variables in a Chinese student sample

While both sleep and optimism have been found to be predictive of well-being, few studies have examined their relationship with each other. Neither do we know much about the mediators and moderators of the relationship. This study investigated (1) the causal relationship between sleep quality and optimism in a college student sample, (2) the role of symptoms of depression, anxiety, and stress as mediators, and (3) how circadian preference might moderate the relationship. Internet survey data were collected from 1,684 full-time university students (67.6% female, mean age = 20.9 years, SD = 2.66) at three time-points, spanning about 19 months. Measures included the Attributional Style Questionnaire, the Pittsburgh Sleep Quality Index, the Composite Scale of Morningness, and the Depression Anxiety Stress Scale-21. Moderate correlations were found among sleep quality, depressive mood, stress symptoms, anxiety symptoms, and optimism. Cross-lagged analyses showed a bidirectional effect between optimism and sleep quality. Moreover, path analyses demonstrated that anxiety and stress symptoms partially mediated the influence of optimism on sleep quality, while depressive mood partially mediated the influence of sleep quality on optimism. In support of our hypothesis, sleep quality affects mood symptoms and optimism differently for different circadian preferences. Poor sleep results in depressive mood and thus pessimism in non-morning persons only. In contrast, the aggregated (direct and indirect) effects of optimism on sleep quality were invariant of circadian preference. Taken together, people who are pessimistic generally have more anxious mood and stress symptoms, which adversely affect sleep while morningness seems to have a specific protective effect countering the potential damage poor sleep has on optimism. In conclusion, optimism and sleep quality were both cause and effect of each other. Depressive mood partially explained the effect of sleep quality on optimism, whereas anxiety and stress symptoms were mechanisms bridging optimism to sleep quality. This was the first study examining the complex relationships among sleep quality, optimism, and mood symptoms altogether longitudinally in a student sample. Implications on prevention and intervention for sleep problems and mood disorders are discussed.

The direction of the relationship between symptoms of insomnia and psychiatric disorders in adolescents

BACKGROUND

This study assessed the direction of the relationship between symptoms of insomnia disorder, depression, various anxiety disorders and obsessive compulsive disorder (OCD) in adolescents after controlling for age, gender, chronotype, and outcome variable at baseline.

METHODS

Data was collected in eight high schools in Adelaide, South Australia, at two time-points approximately 6 months apart. The study was completed by 318 and 255 high school students at baseline and follow-up, respectively, aged 12-18 (M=14.96, SD=1.34) in grades 7-11 at baseline. Hierarchical regression analyses were used to assess each relationship, the first model controlling for age, gender and chronotype, and the second controlling for outcome variable at baseline.

RESULTS

Insomnia symptoms predicted and were predicted by symptoms of each psychiatric disorder in model 1. In model 2, insomnia symptoms predicted symptoms of depression, and vice-versa. Symptoms of insomnia also predicted symptoms of separation anxiety disorder (SAD) once SAD, but not vice-versa, in model 2. Symptoms of obsessive compulsive disorder (OCD) and social phobia (SP) predicted symptoms of insomnia disorder in model 2, but not vice-versa. Insomnia symptoms were no longer related to symptoms of other anxiety disorders in model 2.

LIMITATIONS

The use of self-report measures, and potential predisposing, precipitating, perpetuating or preventative factors were not assessed.

CONCLUSIONS

Symptoms of insomnia disorder are bidirectionally related to depressive symptoms independent from baseline symptoms, and unidirectionally related to symptoms of OCD and SP where OCD and SP are independent risk-factors of the development of insomnia symptoms.

A novel method to visualise and quantify circadian misalignment

The circadian clock governs virtually all processes in the human body, including sleep-wake behaviour. Circadian misalignment describes the off-set between sleep-wake cycles and clock-regulated physiology. This strain is predominantly caused by external (societal) demands including shift work, early school start times and fast travels across time zones. Sleeping at the ‘wrong’ internal time can jeopardise health and safety, and we therefore need a good quantification of this phenomenon. Here, we propose a novel method to quantify the mistiming of sleep-wake rhythms and demonstrate its versatility in day workers and shift workers. Based on a single time series, our Composite Phase Deviation method unveils distinct, subject- and schedule-specific geometries (‘islands and pancakes’) that illustrate how modern work times interfere with sleep. With increasing levels of circadian strain, the resulting shapes change systematically from small, connected forms to large and fragmented patterns. Our method shows good congruence with published measures of circadian misalignment (i.e., Inter-daily Stability and ‘Behavioural Entrainment’), but offers added value as to its requirements, e.g., being computable for sleep logs and questionnaires. Composite Phase Deviations will help to understand the mechanisms that link ‘living against the clock’ with health and disease on an individual basis.

Sleep Disruption in Pediatric Cancer Survivors: Conceptual Framework and Opportunities for Clinical Assessment and Behavioral Treatment

Sleep disruption is a commonly reported consequence of cancer and its treatment in pediatric patients and survivors. This review summarizes common sleep concerns in this population and introduces a multidimensional framework of risk factors specific to childhood cancer that may interact to develop and maintain disrupted sleep. Based on the extant literature, parameters of the cancer and its treatment, physical and social environmental conditions both during and after treatment, changes to family behavior and norms, psychological factors and traumatic stress, and reduced physical activity are hypothesized to be the most pertinent risk factors for disrupted sleep in this population. Potential clinical assessment strategies and behavioral interventions relevant to these considerations are discussed, with reference to the behavioral model of insomnia. The review concludes by offering directions for research and clinical practice, including developing and testing comprehensive assessment tools, intervention effectiveness studies in both oncology and primary care clinics, and efforts to increase patient-provider communication about sleep in pediatric oncology.

Adopted youth and sleep difficulties

Sleep is a critical component of healthy development for youth, with cascading effects on youth’s biological growth, psychological well-being, and overall functioning. Increased sleep difficulties are one of many disruptions that adopted youth may face throughout the adoption process. Sleep difficulties have been frequently cited as a major concern by adoptive parents and hypothesized in the literature as a problem that may affect multiple areas of development and functioning in adopted youth. However, there is limited research exploring this relationship. Using a biopsychosocial framework, this paper reviews the extant literature to explore the development, maintenance, and impact of sleep difficulties in adopted youth. Finally, implications for future research and clinical interventions are outlined.

Self-Regulation and Sleep Duration, Sleepiness, and Chronotype in Adolescents

OBJECTIVE

To determine whether shorter school-night sleep duration, greater daytime sleepiness, and greater eveningness chronotype were associated with lower self-regulation among adolescents.

METHODS

An online survey of 7th- to 12th-grade students in 19 schools in Fairfax County, Virginia Public Schools was conducted in 2015. Self-regulation was measured with the Behavior Rating Inventory of Executive Function, 2nd edition, Screening Self-Report Form. Sleep measures included school night-sleep duration (hours between usual bedtime and wake time), daytime sleepiness (Sleepiness Scale in the Sleep Habits Survey, tertiles), and chronotype (Morningness-Eveningness Scale for Children, continuous score and tertiles). Sociodemographic factors and mental health conditions were analyzed as potential confounders.

RESULTS

Among 2017 students surveyed, the mean age was 15.0 years (range, 12.1-18.9 years), and 21.7% slept <7 hours on school nights. In regression models adjusted for confounders, there was a significant independent association between self-regulation and both chronotype (P < .001) and daytime sleepiness (P < .001) but not sleep duration (P = .80). Compared with those in the lowest tertile of daytime sleepiness, those in the highest tertile had lower (0.59 SD units; 95% confidence interval, 0.48-0.71) self-regulation, as did those in the eveningness tertile of chronotype compared with those in the morningness tertile (0.35 SD units lower; 95% confidence interval, 0.24-0.46).

CONCLUSIONS

Among adolescents, greater daytime sleepiness and greater eveningness chronotype were independently associated with lower self-regulation, but shorter sleep duration was not. Aspects of sleep other than school-night sleep duration appear to be more strongly associated with self-regulation.

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.