Morningness-eveningness in a large sample of German adolescents and adults

Sleep duration and social jetlag in healthy adolescents. Association with anxiety, depression, and chronotype: a pilot study

PURPOSE

Misalignment between sleep opportunity and chronotype preference during adolescence may affect sleep and mental health. The aim of this study was to objectively evaluate sleep duration and social jetlag (SJL) to observe if there is a relationship with anxiety, depression, or chronotype.

METHODS

Community based cohort study (n = 65) was conducted in Northern Europe. Participants recorded their sleep during the regular school schedule for 3 school nights and 2 free nights with FDA-cleared/EU Medical Device Directive (CE-02862) compliant home sleep test. They also completed validated questionnaires to assess (Morningness Eveningness Questionnaire; MEQ), sleepiness (Epworth Sleepiness Scale; ESS), and insomnia (Insomnia Severity Index; ISI), anxiety (General Anxiety Disorder-7; GAD-7), and depression symptoms (Beck's Depression Inventory-II; BDI-II). Data were collected during the last week of February and the first 2 weeks of March, 2023.

RESULTS

Average sleep duration on school nights was 7 h, 15 min, with 18% of participants on average sleeping ≥ 8 h. Average sleep onset was significantly later on free nights (1 hour, 47 minutes; p < 0.0001) causing a high prevalence of moderate-severe SJL, in 71% of participants. Evening chronotypes (prevalence 15.4%) fell asleep later on free nights, causing them to have significantly more SJL (2 hours, 58 minutes) than morning chronotypes (1 hour, 32 minutes) and intermediary chronotypes (1 hour, 36 minutes). Evening chronotypes also had more severe insomnia (ISI + 4.4, p = 0.006; + 4.0, p = 0.001) and greater depressive symptoms (BDI-II + 21.6, p < 0.0001; + 17.1, p < 0.0001). A significant negative correlation was observed between MEQ scores and ESS (r =  - 0.287; p = 0.001), ISI (r =  - 0.343, p < 0.0001), GAD-7 (r =  - 0.185, p < 0.0001), BDI-II (r =  - 0.501, p = 0.0001), and suicidal thoughts (r =  - 0.294, p = 0.017).

CONCLUSION

Adolescents are sleep-deprived and have a high prevalence of SJL that is positively correlated with depressive symptoms and evening chronotype. That evening chronotypes have shorter sleep duration, more severe SJL, and significantly more sleepiness and insomnia, anxiety, and depressive symptoms may indicate possible benefits in identifying this group with the aim to assist them in improving their sleep habits with potentially positive effects on mental health.

Associations of evening-type and insomnia symptoms with depressive symptoms among youths

BACKGROUND

Evening-type and insomnia symptoms are significantly related to each other and independently associated with depressive symptoms, yet few studies have examined the potential interaction between these two conditions. Therefore, we aimed to examine the associations of evening-type and insomnia symptoms with depressive symptoms among Chinese youths, with a specific focus on the joint effects of the two conditions on depressive symptoms.

METHODS

Participants aged between 12 and 25 were invited to participate in an online survey from December 15, 2022, to May 26, 2023. Multivariate logistic regression models and additive interaction models were used to examine the independent and joint effects of chronotypes and insomnia symptoms on depressive symptoms, respectively.

RESULTS

Of the 6145 eligible youths, the prevalence of evening-type and insomnia symptoms were 24.9 % and 29.6 %, respectively. Both evening-type (adjusted OR, [AdjOR]: 3.21, 95 % CI: 2.80-3.67) and insomnia symptoms (AdjOR: 10.53, 95 % CI: 9.14-12.12) were associated with an increased risk of depressive symptoms. In addition, the additive interaction models showed that there is an enhanced risk of depression related to interaction between evening-type and insomnia symptoms (relative excess risk due to interaction, [RERI]: 11.66, 95 % CI: 7.21-16.11).

CONCLUSIONS

The present study provided additional evidence demonstrating the presence of interaction between evening-type and insomnia symptoms, which can lead to a higher risk of depressive symptoms. Our findings argue the need for addressing both sleep and circadian factors in the management of depressive symptoms in young people.

Fundamentals of sleep regulation: Model and benchmark values for fractal and oscillatory neurodynamics

Homeostatic, circadian and ultradian mechanisms play crucial roles in the regulation of sleep. Evidence suggests that ratios of low-to-high frequency power in the electroencephalogram (EEG) spectrum indicate the instantaneous level of sleep pressure, influenced by factors such as individual sleep-wake history, current sleep stage, age-related differences and brain topography characteristics. These effects are well captured and reflected in the spectral exponent, a composite measure of the constant low-to-high frequency ratio in the periodogram, which is scale-free and exhibits lower interindividual variability compared to slow wave activity, potentially serving as a suitable standardization and reference measure. Here we propose an index of sleep homeostasis based on the spectral exponent, reflecting the level of membrane hyperpolarization and/or network bistability in the central nervous system in humans. In addition, we advance the idea that the U-shaped overnight deceleration of oscillatory slow and fast sleep spindle frequencies marks the biological night, providing somnologists with an EEG-index of circadian sleep regulation. Evidence supporting this assertion comes from studies based on sleep replacement, forced desynchrony protocols and high-resolution analyses of sleep spindles. Finally, ultradian sleep regulatory mechanisms are indicated by the recurrent, abrupt shifts in dominant oscillatory frequencies, with spindle ranges signifying non-rapid eye movement and non-spindle oscillations - rapid eye movement phases of the sleep cycles. Reconsidering the indicators of fundamental sleep regulatory processes in the framework of the new Fractal and Oscillatory Adjustment Model (FOAM) offers an appealing opportunity to bridge the gap between the two-process model of sleep regulation and clinical somnology.

Chronotype characteristics of professional athletes in China: a comprehensive descriptive study

BACKGROUND

Chronotype has gained recognition as a significant factor in enhancing athletic performance. This study aimed to deepen our understanding of athletes' sleep chronotypes and provide a foundation for developing evidence-based training and competition programs. By comprehensively describing and analyzing the chronotype characteristics of Chinese professional athletes, considering individual and sports factors, sleep quality and habits, and mental energy, this research aimed to contribute valuable insights to the field.

METHODS

A sample of 1069 professional athletes from sports teams in Shanghai completed the Athlete Sleep Screening Questionnaire and the Athlete Mental Energy Scale to assess chronotype, sleep quality, sleep-influencing habits, and mental energy.

RESULTS

Among athletes, sleep typology fell within the intermediate range, slightly leaning toward morningness. Male athletes and those who engaged in static sports displayed a greater propensity for morningness. Age correlated with a preference for eveningness. High-level athletes exhibited a stronger inclination toward eveningness. Sleep quality issues were associated with an inclination toward eveningness. Daily caffeine intake and the habit of using electronic devices before bedtime are also linked to eveningness. Chronotype demonstrated the ability to predict various dimensions of athletes' mental energy. It was the strongest predictor of vigor, but the loadings were smaller than those of sleep quality.

CONCLUSION

Chinese athletes' chronotypes primarily exhibit distinct characteristics related to individual factors such as gender, sports discipline, and ranking, as well as habits like caffeine consumption and electronic device use. Moreover, these sleep patterns demonstrate predictive capabilities across all dimensions of athletes' mental energy. This study sheds light on Chinese athletes' unique sleep chronotype attributes, enriching our understanding of sleep patterns among professional athletes under various systems. These insights offer an initial basis for enhancing the effectiveness of athlete scheduling and training management.

The association between cholesterol/saturated fat index (CSI) and quality of sleep, and circadian rhythm among overweight and obese women: a cross-sectional study

BACKGROUND

The decline in sleep quality is one of the main public health problems affecting the global population. Some studies have shown that a high-fat diet may be linked to changes in circadian rhythm and sleep quality. The cholesterol/saturated fatty acid index (CSI) determines the amount of cholesterol and saturated fatty acid (SFA) in people's dietary patterns and can affect the quality of sleep and circadian rhythm. However, to date, no studies have investigated the effect of this index on these two variables. Therefore, our aim was to investigate the relationship between CSI on circadian rhythm and sleep quality in obese and overweight women.

METHOD

This cross-sectional study included 378 adult women who were obese or overweight. Using accepted techniques, anthropometric measurements, blood pressure readings, and biochemical variables were evaluated. A validated and trustworthy semi-quantitative food frequency questionnaire (FFQ 147 items) was used to gauge dietary intake. The CSI was measured to find out how much cholesterol and saturated fats were in the diet. Additionally, to assess circadian rhythm and sleep quality, respectively, the valid morning-evening questionnaire (MEQ) and Pittsburgh sleep quality index (PSQI) questionnaires were utilized.

RESULT

The results of the multinomial logistic regression model of our analysis showed that a significant association was observed between circadian rhythm status with CSI score, and participants with one higher unit of CSI had a 7.3% more chance of being in the eveningness group than being in morningness category in the crude model (OR: 1.07; 95% CI 1.00, 1.14; P = 0.026). This association remains marginally significant when adjusting for age, energy intake, BMI, job status, thyroid, and smoking status (OR = 1.08; 95% CI 1.00, 1.16; P = 0.051). The binary logistic regression model showed that after controlling for potentially confounding variables, there was no significant association between sleep quality with CSI score, however, those with one higher unit of CSI had 1.6% more chance of having sleep problems (OR: 1.01; 95% CI 0.96, 1.06; P = 0.503).

CONCLUSION

Our results indicated a direct marginally significant association between CSI with evening type in overweight and obese women. Future studies are needed to clarify the precise link between circadian rhythm and sleep behavior with fatty acid quality index.

The circadian preferences in the context of sociodemographic indicators and lifestyle

Circadian preferences are frequently used as a synonym for chronotype. Both terms are based on different principles and are measured by a variant questionnaire. We focused on circadian preferences, delimited as an individual preference for the timing of various activities, and their relationship to the selected sociodemographic factors. All participants (n = 2068) filled out online questionnaires including MEQ, MCTQ, and sociodemographic information (age, sex, place of residence, marital status, childcare, education, financial security, physical and mental health). Although the concept of chronotype and circadian preference differ, the mutual correlation was high. Our results of the observed variables are similar to other studies. We revealed evening preference is related to a higher probability of living in a big city, having a single life, a higher risk of smoking, worse health status, and worse financial security. We observed a higher social jet lag among them. Our research complies with previous studies, which found that in some areas, people with evening preferences evince worse results. Due to the evening preference, these people are at a disadvantage, and the society's setting for morning operations can lead to a deepening of these differences. We recommend further research, which would focus on the practical application of results to the everyday life of participants to create preventive programs aimed at reducing the negative impact of evening preferences on life.

The fall of vulnerability to sleep disturbances in evening chronotypes when working from home and its implications for depression

Eveningness is distinctively associated with sleep disturbances and depression symptoms due to the misalignment between biological and social clocks. The widespread imposition of remote working due to the COVID-19 pandemic allowed a more flexible sleep schedule. This scenario could promote sleep and mental health in evening-type subjects. We investigated the effect of working from home on sleep quality/quantity and insomnia symptoms within the morningness-eveningness continuum, and its indirect repercussions on depressive symptomatology. A total of 610 Italian office workers (mean age ± standard deviation, 35.47 ± 10.17 years) and 265 remote workers (40.31 ± 10.69 years) participated in a web-based survey during the second contagion wave of COVID-19 (28 November–11 December 2020). We evaluated chronotype, sleep quality/duration, insomnia, and depression symptoms through validated questionnaires. Three moderated mediation models were performed on cross-sectional data, testing the mediation effect of sleep variables on the association between morningness-eveningness continuum and depression symptoms, with working modality (office vs. remote working) as moderator of the relationship between chronotype and sleep variables. Remote working was associated with delayed bedtime and get-up time. Working modality moderated the chronotype effect on sleep variables, as eveningness was related to worse sleep disturbances and shorter sleep duration among the office workers only. Working modality also moderated the mediation of sleep variables between chronotype and depression. The above mediation vanished among remote workers. The present study suggests that evening-type people did not show their characteristic vulnerability to sleep problems when working from home. This result could imply a reduction of the proposed sleep-driven predisposition to depression of late chronotypes. A working environment complying with individual circadian preferences might ensure an adequate sleep quantity/quality for the evening-type population, promoting their mental health.

Investigation of the relationship between chronotype, learning style and academic achievement of university students during distance education in the pandemic period

The purpose of this study was to investigate the relationship between chronotype, learning style, and academic achievement. The study sample consisted of 1884 volunteer undergraduate students from 58 different universities across Turkey. The data were collected online during distance education because of the Covid-19 pandemic. Turkish version of Morningness-Eveningness Questionnaire (MEQ) and Big16 Learning Modality Inventory were used for data collection. The correlation between chronotype and cumulative grade point average (CGPA) scores was analyzed using Spearman's rho, and differences among the chronotypes were analyzed with Kruskal-Wallis test. Chi-square tests with pairwise z-test were used to analyze the relationships between the participants' learning style preferences and chronotypes. Also, ANCOVA analyses were performed to evaluate the interactions of gender × chronotype and gender × learning style on CGPA scores. The results revealed that participants' preference for visual and auditory styles differed by chronotype. Visual learning style was more dominant among morning (M) types, while auditory style was more dominant among evening (E) types. However, the most preferred learning style was visual, followed by auditory and kinesthetic styles for all chronotypes. No relationship was found between chronotype and academic achievement. The CGPA scores of the participants with kinesthetic learning style were lower than the participants with auditory and visual learning styles. The female participants had higher CGPA score than males. However, the CGPA scores did not differ for both male and female participants with different chronotype and learning style preferences. From the results, we suggest that academic achievement can be enhanced by consideration of students' learning style preferences for all chronotypes.

Sex differences in the relationship between morningness-eveningness components, mood and well-being among Bangladeshi university students

On the Morningness/Eveningness (M/E) continuum, eveningness has been related to mood disorder and poor well-being. M/E differs between men and women throughout their lifespan. However, there is a lack of information on sex differences in the relationship between M/E, mood, and well-being. This study aimed to test sex differences in the M/E, mood, and well-being relationship with consideration of two components of M/E, morning affect, and morning preference. A sample of 981 Bangladeshi university students (607 men) aged 18 to 27 (M = 21.95) completed Bangla versions of the Composite Scale of Morningness (CSM), BRUnel Mood Scale (BRUMS), and Positive Mental Health scale (PMH-scale) through an online survey. Multiple regression analyses were used to test the relationship of M/E components with mood and well-being. The results showed that the relationship between M/E, mood, and well-being was greater in women than in men. A lower score on both M/E components was related to higher negative moods (anger, confusion, depression, fatigue, and tension) and poor well-being. In regression analysis, only morning affect was found to be significant, which means that morning affect mainly contributes to the relation between M/E, mood, and well-being. Finally, sex by morning affect interaction indicated that the relation was higher for women. Therefore, higher eveningness could be more hazardous for women than men. Greater insight into the independent contribution of morning affect may facilitate understanding of the chronotype effects on psychological outcomes in men and women.

Validation of the Chinese version of the Munich Chronotype Questionnaire (MCTQHK) in Hong Kong Chinese youths

Chronotype, referred to as an individual's diurnal preference of timing for rest and activity, can be subjectively measured using the Munich Chronotype Questionnaire (MCTQ). However, the validity of MCTQ has yet to be tested in the youth population. In addition, it remains uncertain if MCTQ is a good measure of chronotype in individuals with insomnia. The current study aimed to validate the Chinese version of MCTQ (MCTQ^HK) in the youth population and to explore the utility of MCTQ^HK in individuals with insomnia. The original MCTQ was translated into Chinese language using the translation-back-translation method. Part one of this study included 988 youths who completed a battery of self-report questionnaires online consisting of the MCTQ^HK and the morningness-eveningness questionnaire (MEQ) for the measures of circadian preference, Insomnia Severity Index (ISI) to assess insomnia symptoms, and Patient Health Questionnaire (PHQ-9) to measure depressive symptoms. Test-retest reliability was examined in 442 participants at one-month follow-up. Of the overall sample, 69 participants were randomly drawn to complete the second part of the study, which included prospective 7-day actigraphy monitoring and a further subset (n = 40) additionally completed a laboratory-based assessment of dim-light melatonin onset (DLMO) as a circadian phase marker. A total of 659 participants with valid responses were finally included in the analyses of the data collected from part one of the study (female = 67.7%; mean age: 20.7 ± 2.02). Results showed that MCTQ parameters, namely the midpoint of sleep on free days (MSF), midpoint of sleep on workdays (MSW), and midpoint of sleep adjusted for sleep debt (MSFsc), were significantly correlated with MEQ score (r = -.514 to -.650, p < .01). Test-retest reliability for MCTQ^HK was good (intraclass correlation = 0.75 to 0.84). Later MSFsc was significantly associated with greater insomnia and depressive symptoms after controlling for age and sex. All MCTQ parameters showed significant correlations with actigraphy-based midpoint of sleep and circadian rhythm parameters, i.e., acrophase and L5 onset (r = .362 to .619, p < .01), as well as DLMO (r = .393 to .517, p < .05). The associations remained significant after controlling for age. MSFsc derived from MCTQ was significantly correlated with MEQ score in both the healthy sleepers and participants with insomnia (as defined by ISI > 14), r = -.600, p < .001 and r = -.543, p < .001, respectively. The present study demonstrated that MCTQ^HK is suitable for assessing chronotype with good reliability and validity in Chinese youths and supported the utility of MCTQ^HK in individuals with insomnia.

Sleep during COVID-19-related school lockdown, a longitudinal study among high school students

There has been great concern about the impact of coronavirus disease 2019 (COVID-19)-related school lockdown on adolescent health. The aim of the present study was to compare sleep patterns before and during COVID-19-related school lockdown, in a large sample of high school students. The present study is based a prospective, longitudinal survey on adolescent sleep health. Phase 1 was conducted in 2019, whereas phase 2 was conducted in 2020 (response rate 60.2%), during the last 10 days of a 60-day long school lockdown. Main outcomes comprised sleep parameters from the Munich ChronoType Questionnaire (MCTQ). A total of 2,022 students provided valid responses to MCTQ in both survey phases. Results showed later sleep timing on schooldays in 2020 compared to 2019 (36 min later bedtimes, Cohen's d = 0.56; 1:35 hr later rise times, Cohen's d = 1.44). Time spent in bed on schooldays increased from 8:20 to 9:19 hr (Cohen's d = 0.78), and sleep duration increased by 45 min (Cohen's d = 0.49). The proportion of adolescents obtaining the recommended ≥8 hr of sleep on schooldays increased from 13.4% (2019) to 37.5% during the lockdown. Social jetlag was reduced from 2:37 hr (2019) to 1:53 hr (2020, Cohen's d = 0.59). Results points to a potential advantageous effect of school lockdown in terms of increased school day sleep duration and reduced social jetlag. As sleep is important for mental and somatic health, it is conceivable that increased sleep duration offered some protection against harmful aspects of the COVID-19 pandemic and associated social restrictions. Future studies should address possible associations between sleep changes and health during COVID-19-related school lockdown.

Circadian typology and implications for adolescent sleep health. Results from a large, cross-sectional, school-based study

STUDY OBJECTIVES

To investigate circadian typology in a large, representative sample of Norwegian adolescents, and its implications for sleep health.

METHODS

The sample included 3920 1^st year high school students aged 16-17 years. Respondents completed a web-based survey, including the short version of the Horne-Ostberg Morningness-Eveningness Questionnaire (rMEQ), the Munich Chronotype Questionnaire (MCTQ) and items on sleep-related behaviors (eg electronic media usage in bed, consumption of caffeinated beverages), sleep beliefs and daytime sleepiness. Data were analyzed using one-way ANOVAs and Chi-squared tests.

RESULTS

In all, 7.8% were categorized as morning, 52.3% as intermediate and 39.9% as evening types, respectively. Evening types had later sleep timing, longer sleep latency, more social jetlag and shorter school day sleep duration than morning types, with intermediate types displaying a sleep pattern between these two extremes. None of the circadian types met the minimum recommended amount of sleep on school nights (ie 8+ hours), and only morning types had a mean sleep duration of 7+ hours (7:19 h, nearly 1 h more than evening types who slept 6:20 h, p < 0.001). Evening types reported more use of electronic media in bed, more consumption of caffeinated beverages and more daytime sleepiness than the other circadian types. They were also less satisfied with their school day sleep duration and perceived it more difficult to change their sleep pattern.

CONCLUSIONS

Results from this study suggest that eveningness represents a sleep health challenge for older adolescents.

Chronotype distribution in the Chinese population

Purpose:

Individual chronotypes are reported to be closely associated with mood, health status, and even disease progression. However, no reports of chronotype distribution in the Chinese population have been made available to date.

Methods:

We performed a chronotype survey using the classic Morningness–Eveningness Questionnaire both online and offline. The webpage-based online survey was distributed via a social network application on mobile phones. The offline survey was distributed to local primary and middle schools. A total of 9476 questionnaires were collected, of which 8395 were valid. The mean age of the participants was 30.38 ± 11.47 years, and 37.38% were male.

Results:

Overall, the Chinese chronotypes showed a near-normal distribution with a slight shift toward eveningness. When analyzed in different age groups, the overall Chinese population was shown to be “latest” in their early twenties. In the young population, two significant points of change in chronotype were identified at the ages of 10 and 16 years. The chronotype composition remained relatively stable during early adulthood (from 17 to 28 years of age).

Conclusion:

This study generated the first overview of chronotype distribution in the Chinese population and will serve as essential background data for future studies.

Circadian typology is related to emotion regulation, metacognitive beliefs and assertiveness in healthy adults

Circadian typology has been related to several mental health aspects such as resilience, perceived well-being, emotional intelligence and psychological symptoms and disorders. However, the relationship between circadian typology and emotion regulation, metacognitions and assertiveness, which constitute core constructs related to psychological well-being and psychopathology, remain unexplored. This study aims to analyze whether circadian typology is related with those three constructs, considering the possible influence of sex. 2283 participants (833 women), aged 18–60 years (30.37 ± 9.26 years), completed the reduced Morningness-Eveningness Questionnaire, the Emotion Regulation Questionnaire, the Meta-Cognitions Questionnaire 30, and the Rathus Assertiveness Schedule. Main effects were observed between circadian typology and cognitive reappraisal, metacognitions, negative beliefs of uncontrollability and danger, cognitive confidence, cognitive self-consciousness, and assertiveness (F_(2,2276) > 4.80, p < 0.009, η_p² > 0.004, in all cases). Morning-type participants scored lower than evening-type in general metacognitive beliefs, negative beliefs of uncontrollability and danger, cognitive confidence, and cognitive self-consciousness, and higher than evening-type in cognitive reappraisal and assertiveness, while neither-type exhibited intermediate scores (p < 0.033 in all cases). According to the results, evening-type individuals might display a higher tendency to support maladaptive beliefs about thinking itself as well as a lesser tendency to reappraise a potentially emotion eliciting situations in order to modify its meaning and its emotional impact and to exert their rights respectfully. This new evidence improves the understanding of the relationships between circadian typology and psychological factors related to psychological well-being and psychopathology. Results implications for the onset and maintenance of psychological problems are discussed. Although future longitudinal studies are needed, results emphasize evening-type as a risk factor for the development of psychological disturbances and morning-type as a protective factor against those.

Circadian preferences of birdwatchers in Poland: do "owls" prefer watching night birds, and "larks" prefer daytime ones?

Birdwatching is a very popular and increasing leisure activity, and the study and observation of birds is more popular in the morning due to the greater activity among birds at that time of day. The aim of our study was to find out whether there was a relationship between the circadian preference of observers and their favourite bird species and whether it was influenced by such factors as professional status, age and gender. In an e-mail survey we asked a total of 433 Polish ornithologists (professionals) or birdwatchers (non-professionals) for their morningness–eveningness preferences (four categories) and favourite (open choice) bird species and received 143 responses. The temporal (circadian) preferences of respondents declined from early morning (35.7%) to evening/nighttime (11.4%). Circadian preference categories differed significantly by age, with early morning respondents significantly older. These preference categories did not differ significantly in terms of response time to the survey invitation or in the percentage of their favourite birds that were categorised as daytime birds. A total of 204 species were identified as favourite birds of which 34 species were mentioned by five or more respondents, with only two, the common crane Grus grus and the Eurasian pygmy owl Glaucidium passerinum mentioned by more than 10% of respondents. The white stork Ciconia ciconia was more popular with professionals than non-professionals and the swift Apus apus less popular. A significant gender × circadian preference interaction was detected for the percentage of favourite birds categorised as daytime birds, with fewer daytime birds among early morning female recorders. The presented results are obviously of a correlative nature, but open the door for further, more advanced study and suggest there may be a need to investigate temporal biases when analysing citizen-based data.

Sleep and Circadian Rhythm Disorder in Bipolar Affective Disorder

Symptoms of affective disorders encompass a range of changes to biological processes such as sleep and appetite. These processes are regulated over a 24-h cycle known as the circadian rhythm. Sleep is a particularly useful marker of this rhythm as it is readily measurable and functionally significant. Sleep disturbance is common in bipolar affective disorder and may act as a marker, and precipitant, of relapse. Circadian rhythms are modulated by environmental and social cues and have been shown to be influenced by treatment in BPAD. As such understanding of circadian rhythms may lead to a better understanding of the pathophysiology of BPAD and its treatment. This chapter will explore the neurobiology of the circadian clock and the putative role of circadian rhythm dysregulation in the pathophysiology and treatment of bipolar affective disorder (BPAD).

Social Jetlag and Chronotypes in the Chinese Population: Analysis of Data Recorded by Wearable Devices

Background

Chronotype is the propensity for a person to sleep at a particular time during 24 hours. It is largely regulated by the circadian clock but constrained by work obligations to a specific sleep schedule. The discrepancy between biological and social time can be described as social jetlag (SJL), which is highly prevalent in modern society and associated with health problems. SJL and chronotypes have been widely studied in Western countries but have never been described in China.

Objective

We characterized the chronotypes and SJL in mainland China objectively by analyzing a database of Chinese sleep-wake pattern recorded by up-to-date wearable devices.

Methods

We analyzed 71,176 anonymous Chinese people who were continuously recorded by wearable devices for at least one week between April and July in 2017. Chronotypes were assessed (N=49,573) by the adjusted mid-point of sleep on free days (MSFsc). Early, intermediate, and late chronotypes were defined by arbitrary cut-offs of MSFsc <3 hours, between 3-5 hours, and >5 hours. In all subjects, SJL was calculated as the difference between mid-points of sleep on free days and work days. The correlations between SJL and age/body mass index/MSFsc were assessed by Pearson correlation. Random forest was used to characterize which factors (ie, age, body mass index, sex, nocturnal and daytime sleep durations, and exercise) mostly contribute to SJL and MSFsc.

Results

The mean total sleep duration of this Chinese sample is about 7 hours, with females sleeping on average 17 minutes longer than males. People taking longer naps sleep less during the night, but they have longer total 24-hour sleep durations. MSFsc follows a normal distribution, and the percentages of early, intermediate, and late chronotypes are approximately 26.76% (13,266/49,573), 58.59% (29,045/49,573), and 14.64% (7257/49,573). Adolescents are later types compared to adults. Age is the most important predictor of MSFsc suggested by our random forest model (relative feature importance: 0.772). No gender differences are found in chronotypes. We found that SJL follows a normal distribution and 17.07% (12,151/71,176) of Chinese have SJL longer than 1 hour. Nearly a third (22,442/71,176, 31.53%) of Chinese have SJL<0. The results showed that 53.72% (7127/13,266), 25.46% (7396/29,045), and 12.71% (922/7257) of the early, intermediate, and late chronotypes have SJL<0, respectively. SJL correlates with MSFsc (r=0.54, P<.001) but not with body mass index (r=0.004, P=.30). Random forest model suggests that age, nocturnal sleep, and daytime nap durations are the features contributing to SJL (their relative feature importance is 0.441, 0.349, and 0.204, respectively).

Conclusions

Our data suggest a higher proportion of early compared to late chronotypes in Chinese. Chinese have less SJL than the results reported in European populations, and more than half of the early chronotypes have negative SJL. In the Chinese population, SJL is not associated with body mass index. People of later chronotypes and long sleepers suffer more from SJL.

Gender differences in chronotype diminish with age: a meta-analysis based on morningness/chronotype questionnaires

Chronotype is an individual difference trait that is closely linked to biological variables. Usually, men and women differ in their chronotype with men being more evening oriented than women. The aim of the study was to assess gender differences in chronotype based on a systematic review and meta-analysis. In addition, many recent studies do not report gender differences any more although researchers collected data on men and women. This motivated us to contact many researchers directly to obtain and use these additional data. We included 164 studies giving 201 effect size measures in a data set, which only included the most commonly used questionnaires (MEQ, rMEQ and CSM) totaling 186,289 participants in total, of which 75,622 were men and 110,667 were women. We calculated an effect size of the standardized mean difference of -0.072 (95% CI from -0.062 to -0.082) in the fixed effects and of -0.066 (95% CI from -0.043 to- 0.089) in the random effects model. Men were on average more evening oriented than women. Type of questionnaire did not influence the standardized mean difference in chronotype between genders. Mean age, standard deviation of age and publication year (p ≤ 0.05) were found to have significant effects on the standardized mean difference in chronotype between genders. The standardized mean difference in chronotype between genders is predicted to change from negative to positive with increasing mean age (young women were more morning orientated than young men, but older women were less morning orientated than older men). This suggests that the differences between men and women diminish with time. The standardized mean difference in chronotype between genders is decreasing with increasing publication year, as well as with high variation in age of the samples. Abbreviations: CSM: Composite Scale of Morningness (Smith et al. 1989); MEQ: Morningness-Eveningness Questionnaire (Horne and Ostberg, 1976); rMEQ: reduced Morningness-Eveningness Questionnaire (Adan & Almiral, 1991); SMD: standardized mean difference (measure of effect size).

Factorial Structure of the Morningness-Eveningness-Stability-Scale (MESSi) and Sex and Age Invariance

Assessing morningness-eveningness preferences (chronotype), an individual characteristic that is mirrored in daily mental and physiological fluctuations, is crucial given their overarching influence in a variety of domains. The current work aimed to investigate the best factor structure of an instrument recently presented to asses this characteristic: the Morningness-Eveningness-Stability-Scale improved (MESSi). For the first time, the originally proposed three-factor structure was pitched against a uni- and a two-factor solution. Another novelty was to establish that the best-fitting model would be invariant in relation to sex and age, two variables that influence chronotype. A Confirmatory Factor Analyses on the data obtained from a sample of 2096 German adults (age: 18–76; M = 25.5, SD = 7.64) revealed that the originally proposed three-factor structure of the MESSi – Morning Affect, Eveningness, and Distinctness – was the only one to achieve acceptable fit indicators. Furthermore, each scale obtained good internal consistency. In order to assess age invariance, following the literature on development and chronotype, our sample was divided into three age groups: 18–21 years, 22–31 years, and 32 years or older. Full measurement invariance of the three-factor model was found for sex and age. Regarding differences between sexes, females did not differ significantly from males in Morning Affect, but scored significantly lower on Eveningness and higher on Distinctness; this last result has been consistent across validation studies of the MESSi. With respect to age differences, the oldest group scored lower on Eveningness and Distinctness in comparison with the other two age-groups; the intermediate group (age: 22–31) scored lower on Morning Affect when compared to both the younger and older age groups. Additionally, both Eveningness and Distinctness were negatively correlated with age. This latter relation has been consistently reported in other validation studies. Our results reinforce the idea that the MESSi assesses three different components of chronotype in a reliable manner and that this instrument can be used to explore sex and age differences.

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.

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.

Morningness-Eveningness questionnaire in bipolar disorder

The Morningness-Eveningness Questionnaire (MEQ) is among the most commonly used scales to measure chronotype. We aimed to evaluate psychometric properties and clinical correlates of MEQ in bipolar disorder. Patients with a clinical diagnosis of bipolar disorder (n = 53) answered questionnaires for chronotype (MEQ), mood (Quick Inventory of Depressive Symptoms-16, Altman Self-Rating Mania Scale), insomnia (Athens Insomnia Scale, AIS), and sleepiness (Epworth Sleepiness Scale). Mood was evaluated using Montgomery-Åsberg Depression Rating Scale and Young Mania Rating Scale. The MEQ showed high internal consistency with Cronbach's alpha of .85. Lower MEQ scores (eveningness) correlated with insomnia (AIS) (r = -.34, p = .013). The estimate for eveningness (13/53, 24.5%) in our study was higher than in comparable studies in the general population. Patients on lithium exhibited a higher mean MEQ score (56.0 on lithium vs 46.9 with no lithium, p = .007), whereas this score was lower for patients on an antidepressant (46.0 on antidepressants vs 52.6 with no antidepressants, p = .023). We conclude that the MEQ score is psychometrically reliable. However, future studies should further evaluate the association of medication with chronotype. Validation of categorical cut-offs for MEQ in a larger sample of bipolar patients is needed to increase clinical utility.

What predicts inattention in adolescents? An experience-sampling study comparing chronotype, subjective, and objective sleep parameters

OBJECTIVE

Many adolescents sleep insufficiently, which may negatively affect their functioning during the day. To improve sleep interventions, we need a better understanding of the specific sleep-related parameters that predict poor functioning. We investigated to which extent subjective and objective parameters of sleep in the preceding night (state parameters) and the trait variable chronotype predict daytime inattention as an indicator of poor functioning.

METHODS

We conducted an experience-sampling study over one week with 61 adolescents (30 girls, 31 boys; mean age = 15.5 years, standard deviation = 1.1 years). Participants rated their inattention two times each day (morning, afternoon) on a smartphone. Subjective sleep parameters (feeling rested, positive affect upon awakening) were assessed each morning on the smartphone. Objective sleep parameters (total sleep time, sleep efficiency, wake after sleep onset) were assessed with a permanently worn actigraph. Chronotype was assessed with a self-rated questionnaire at baseline. We tested the effect of subjective and objective state parameters of sleep on daytime inattention, using multilevel multiple regressions. Then, we tested whether the putative effect of the trait parameter chronotype on inattention is mediated through state sleep parameters, again using multilevel regressions.

RESULTS

We found that short sleep time, but no other state sleep parameter, predicted inattention to a small effect. As expected, the trait parameter chronotype also predicted inattention: morningness was associated with less inattention. However, this association was not mediated by state sleep parameters.

CONCLUSIONS

Our results indicate that short sleep time causes inattention in adolescents. Extended sleep time might thus alleviate inattention to some extent. However, it cannot alleviate the effect of being an 'owl'.

Reduced Effective Emotion Regulation in Night Owls

Previous research has demonstrated a clear link between late chronotype and depression. The vulnerability factors underpinning this link, however, are unclear. Here the relationship between two specific emotion regulation strategies, cognitive reappraisal and expressive suppression, and chronotype was investigated using multiple regression. Two hundred and forty participants (age range 18-80, 189 females) completed validated self-report questionnaires assaying chronotype, neuroticism, depressive symptomatology, sleep quality, and emotion regulation. Eveningness was associated with increased expressive suppression, and morningness was associated with increased cognitive reappraisal after controlling for age, gender, depressive symptomatology, neuroticism, and sleep quality. Trait expressive suppression and reduced cognitive reappraisal are known to increase depression risk. Our results suggest that eveningness is associated with impaired emotion regulation, which may confer risk for future depression. These findings suggest modifiable markers that could be therapeutically targeted to prevent the onset of depression in late chronotype individuals.

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.

Conscientiousness but not agreeableness mediates females' tendency toward being a morning person

Individuals differ in their chronotype, and some are identified as morning ones and others as evening ones. Earlier studies showed that women were higher on morningness, conscientiousness, and agreeableness. In this study, we aimed at exploring the mediational effects of conscientiousness and agreeableness in the relationship of gender and morningness-eveningness. Participants were 669 university students. Results supported positive relationships between morningness and conscientiousness and agreeableness and between conscientiousness and agreeableness. Females were higher on all these three variables. Mediation analyses suggested that the effect of gender (here females) on chronotype (here morningness) was mediated by conscientiousness but not agreeableness so that after the mediation partially occurred, the gender's effect did not remain significant anymore. This study backed our hypothesis that conscientiousness might play a more pronounced role than the intrinsic diurnal rhythm concerning the sex differences in chronotype.

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.

Procedural Memory Consolidation in Attention-Deficit/Hyperactivity Disorder Is Promoted by Scheduling of Practice to Evening Hours

In young adults without attention-deficit/hyperactivity disorder (ADHD) training on a novel movement sequence results not only in large within-session (online) gains in task performance but also in additional (delayed, off-line) gains in the performance, expressed after an interval of sleep. In contrast, young people with ADHD, given an identical practice, were shown to improve online but expressed much smaller delayed gains overnight. As delayed gains in performance are taken to reflect procedural ("how to") memory consolidation processes, this may explain skill learning deficits in persons with ADHD. However, motor training is usually provided in morning sessions, and, given that persons with ADHD are often evening types, chronobiological constraints may constitute a hidden factor. Here, we tested the hypothesis that evening training, compared to morning training, would result in larger overnight consolidation gains following practice on a novel motor task in young women with ADHD. Participants with (N = 25) and without (N = 24) ADHD were given training on a finger opposition sequence tapping task, either in the morning or at evening. Performance was assessed before and immediately after training, overnight, and at 2 weeks post-training. Individuals with ADHD reported a general preference for evening hours. Evening training was equally effective in participants with and without ADHD, both groups showing robust consolidation gains in task performance overnight. However, the ability to express delayed gains overnight was significantly reduced in participants with ADHD if trained in the morning. Typical peers were as effective in expressing overnight consolidation phase gains irrespective of the time-of-day wherein the training session was afforded. Nevertheless, even after morning training, participants with ADHD fully retained the gains acquired within the first 24 h over an interval of about 2 weeks. Our results suggest that procedural memory consolidation processes are extant and effective in ADHD, but require that specific biobehavioral conditions be met. The affordance of training in the evening hours can relax some of the constraints on these processes in ADHD. The current results are in line with the notion that the control of what is to be retained in procedural memory is atypical or more stringent in ADHD.