Parental enforcement of bedtime during childhood modulates preference of Japanese junior high school students for eveningness chronotype

For Whom (and When) the Time Bell Tolls: Chronotypes and the Synchrony Effect

Circadian rhythms are powerful timekeepers that drive physiological and intellectual functioning throughout the day. These rhythms vary across individuals, with morning chronotypes rising and peaking early in the day and evening chronotypes showing a later rise in arousal, with peaks in the afternoon or evening. Chronotype also varies with age from childhood to adolescence to old age. As a result of these differences, the time of day at which people are best at attending, learning, solving analytical problems, making complex decisions, and even behaving ethically varies. Across studies of attention and memory and a range of allied areas, including academic achievement, judgment and decision-making, and neuropsychological assessment, optimal outcomes are found when performance times align with peaks in circadian arousal, a finding known as the synchrony effect. The benefits of performing in synchrony with one's chronotype (and the costs of not doing so) are most robust for individuals with strong morning or evening chronotypes and for tasks that require effortful, analytical processing or the suppression of distracting information. Failure to take the synchrony effect into consideration may be a factor in issues ranging from replication difficulties to school timing to assessing intellectual disabilities and apparent cognitive decline in aging.

Social jetlag longitudinally predicts internalizing and externalizing behavior for adolescent females, but not males

Biological changes contribute to preferences for later bed and wake times during adolescence, yet the social constraints of school start times necessitate early wake times. This often results in social jetlag (i.e. misalignment between preferred sleep timing on weekends and school days). We examined whether social jetlag predicts adolescent internalizing and externalizing behavior over time and/or whether associations differ based on sex. We used data from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development Study (n = 767) to test whether social jetlag at 6th grade (ages 12-13 years) predicted internalizing and externalizing behavior at age 15 years and whether child sex moderated associations. Controlling for internalizing and externalizing behavior at 6th grade (ages 12-13 years), results were that social jetlag at 6th grade (ages 12-13 years) predicted more internalizing and externalizing behaviors at age 15 for females, but not males. These findings show that social jetlag during early adolescence confers risk for internalizing and externalizing behavior in females at mid-adolescence. Greater attention should be placed on identifying and addressing social jetlag in adolescent females.

Chronotype and time-of-day effects on spatial working memory in preschool children

STUDY OBJECTIVES

Spatial working memory (SWM) capacity subserves complex cognitive functions, yet it is unclear whether individual diurnal preferences and time-of-day influence SWM in preschool children. The main and interaction effects of chronotype and time-of-day on SWM and SWM differences in preschoolers with different chronotypes within each time-of-day group will be examined.

METHODS

We studied a subset of typically developing 4.5-year-olds taking part in a birth cohort study (n = 359). The Children's Chronotype Questionnaire categorized children into morning-, intermediate-, and evening-types. Using a computerized neuropsychological test (Cambridge Neuropsychological Test Automated Battery), SWM was determined from the total number of between-search errors (ie, between search-total errors) and Strategy scores. Higher between search-total errors or lower Strategy scores indicated worse SWM. Time-of-day was categorized into late morning (10:00 am to 11:59 am), afternoon (12:00 pm to 3:59 pm), and late afternoon (4:00 pm to 6:30 pm). In a subsample (n = 199), caregiver-reported chronotype was validated using actigraphy-measured sleep midpoint.

RESULTS

After controlling for ethnicity, no significant main and interaction effects of chronotype and time-of-day on between search-total errors and Strategy scores were seen (all P > .05). However, evening-types outperformed morning-types (ie, lower mean between search-total errors) in the late afternoon (P = .013) but not in the late morning and afternoon (all P > .05). Actigraphy data in the subsample confirmed that evening-types had later sleep midpoints during weekdays and weekends (P < .001).

CONCLUSIONS

Since evening-type preschoolers had better SWM in the late afternoon compared to morning-type preschoolers, this gives insights into optimal learning opportunities in early childhood education.

CITATION

Abdul Jafar NK, Tham EKH, Eng DZH, et al. Chronotype and time-of-day effects on spatial working memory in preschool children. J Clin Sleep Med. 2023;19(10):1717-1726.

Factors Underpinning the Shift to Eveningness during Early Adolescence: Pubertal Development and Family Conflicts

Biological and psychosocial factors have been related to the shift to eveningness during early adolescence but it is necessary to study them from a longitudinal perspective. This longitudinal study examined the contribution of these factors to the onset of a shift towards eveningness in early adolescence. A sample of 440 (49.9% boys) Spanish adolescents were assessed for pubertal development, family conflicts, and morningness/eveningness. The same measures were taken twice at the age of 12 and one year later (T1: M = 12.47, SD = 0.75 and T2: M = 13.64, SD = 0.78). Pubertal development and family conflicts were considered predictors of morningness/eveningness in a mixed-effects multilevel model. The developmental shift towards eveningness appeared in girls but not in boys. The shift was related to more advanced pubertal development and more conflicts in the family. This study has implications for shaping healthy sleep habits in adolescents and possible interventions focused on family dynamics.

Sleep patterns in childhood: a longitudinal assessment from the Generation XXI birth cohort

OBJECTIVE

To describe sleep-wake patterns in young children, based on sleep characteristics in early infancy and preschool ages, identifying their main sociodemographic characteristics, and to assess the association between different sleep characteristics at both ages.

METHOD

We included 1092 children from the Generation XXI birth cohort, evaluated at six months and four years of age, by face-to-face interviews. Sleep patterns were constructed through latent class analysis and structured equation modeling, including data on wake-up time and bedtime, afternoon naps, locale of nighttime sleep and night awakenings. To estimate the association between sociodemographic characteristics and sleep patterns, odds ratios and 95% confidence intervals were computed using logistic regression.

RESULTS

Two sleep patterns were identified through latent class analysis: pattern 1 was characterized by earlier bedtime and wake-up times, while pattern 2 was defined by later times. When compared with pattern 1, pattern 2 was more frequent among children whose mothers had changed from partnered to not partnered until preschool age and those who did not stay at the kindergarten, and was less common among those with siblings. Through structured equation modeling, an aggregating factor was identified at preschool age, which was mainly correlated with bedtime and wake-up time. A positive association between sleep characteristics evaluated in early infancy and in preschool ages was observed.

CONCLUSIONS

Sleep patterns and circadian sleep preferences seem to be developed early in life, which highlight the importance of promoting an adequate sleep hygiene from infancy, assuming its impact on sleep quality during the life course.

Morningness in German and Spanish students: a comparative study

Humans show pronounced individual differences in circadian orientation. Transcultural comparisons are interesting since biological (or environmental) factors together with cultural ones may contribute to differences in morningness–eveningness. We compared Spanish and German undergraduates using the Composite Scale of Morningness (CSM) to assess circadian preferences. Confirmatory and multiple groups confirmatory factor analysis were used to assess factor structure and structural invariance across countries. The results showed that a three‐factor model of morningness best characterises the CSM structure of both samples. Partial factorial invariance (factor loadings) across countries was demonstrated for the factors ‘morningness’ and ‘morning alertness’. Scores of both factors were higher in German students. Potential cultural and biological explanations for the differences are discussed. Copyright © 2007 John Wiley & Sons, Ltd.

Validation of the Chinese Version of the Children's ChronoType Questionnaire (CCTQ) in school-aged children

The Children's ChronoType Questionnaire (CCTQ) is a valid and reliable measure for assessing prepubertal children aged 4-11 years. The CCTQ is a parent-reported, 27-item questionnaire consisting of sleep-wake parameters for scheduled and free days (16 items), a morningness/eveningness scale (M/E, 10 items), and a five-point, single-item, chronotype score. The CCTQ has been translated into different languages, but a Chinese version is not available. In the present study, we aimed to produce a Chinese version of the CCTQ and test its validity and reliability on school-aged children. A total of 555 children aged 7-11 years were recruited from five primary schools. The parents were told to complete the CCTQ and record their child's sleep pattern in a 7-day sleep diary. Sixty-six children and their parents were invited to participate in determining the test-retest reliability of the CCTQ over a 2-week interval, and their sleep patterns were assessed using a sleep diary. The internal consistency of the Chinese CCTQ M/E score as measured by Cronbach's alpha was acceptable (0.74). Regarding the test-retest reliability of the instrument, moderate to strong Spearman's correlation coefficients were found for most of the CCTQ - sleep-wake items (ρ = 0.52-0.86) and for the CCTQ-M/E total score (ρ = 0.78). For the concurrent validity, Spearman's correlations between the sleep-wake parameters of the CCTQ and the sleep diary were moderate to high on both the scheduled days (ρ = 0.54 to 0.87) and free days (ρ = 0.36 to 0.60). For the correlations measured with actigraphs, significant correlations were found in the CCTQ sleep-wake parameters, including bedtime, get-up time, sleep latency, sleep period, time in bed, and mid-sleep point on both the scheduled (ρ = 0.31 to 0.76) and free days (ρ = 0.27 to 0.52), but not in sleep latency and sleep period on free days. The results of the present study suggest that the Chinese version of the CCTQ is a reliable and valid tool for assessing chronotypes in Chinese school-aged children in Hong Kong.

Co-Sleeping among School-Aged Anxious and Non-Anxious Children: Associations with Sleep Variability and Timing

Little is known about the co-sleeping behaviors of school-aged children, particularly among anxious youth who commonly present for the treatment of sleep problems. The current study examined the occurrence of co-sleeping in both healthy and clinically anxious children and its associated sleep patterns. A total of 113 children (ages 6-12), 75 with primary generalized anxiety disorder and 38 healthy controls, participated along with their primary caregiver. Families completed structured diagnostic assessments, and parents reported on their child's co-sleeping behaviors and anxiety severity. Children provided reports of anxiety severity and completed one week of wrist-based actigraphy to assess objective sleep patterns. A significantly greater proportion of anxious youth compared to healthy children co-slept, and greater anxiety severity was related to more frequent co-sleeping. Co-sleeping in anxious youth was associated with a delay in sleep timing and with greater sleep variability (i.e., more variable nightly sleep duration). All analyses controlled for child age, race/ethnicity, family income, and parental marital status. Co-sleeping is highly common in anxious school-aged children, with more than 1 in 3 found to co-sleep at least sometimes (2-4 times a week). Co-sleeping was even more common for youth with greater anxiety severity. Increased dependence on others to initiate and maintain sleep may contribute to poorer sleep in this population via shifted schedules and more variable sleep patterns.

Chronotype: Implications for Epidemiologic Studies on Chrono-Nutrition and Cardiometabolic Health

Chrono-nutrition is an emerging research field in nutritional epidemiology that encompasses 3 dimensions of eating behavior: timing, frequency, and regularity. To date, few studies have investigated how an individual's circadian typology, i.e., one's chronotype, affects the association between chrono-nutrition and cardiometabolic health. This review sets the directions for future research by providing a narrative overview of recent epidemiologic research on chronotype, its determinants, and its association with dietary intake and cardiometabolic health. Limited research was found on the association between chronotype and dietary intake in infants, children, and older adults. Moreover, most of the evidence in adolescents and adults was restricted to cross-sectional surveys with few longitudinal cohorts simultaneously collecting data on chronotype and dietary intake. There was a gap in the research concerning the association between chronotype and the 3 dimensions of chrono-nutrition. Whether chronotype modifies the association between diet and cardiometabolic health outcomes remains to be elucidated. In conclusion, further research is required to understand the interplay between chronotype, chrono-nutrition, and cardiometabolic health outcomes.

Teenage night owls or early birds? Chronotype and the mental health of adolescents

Evidence suggests that the timing of sleep (chronotype) impacts mental health in young people, but previous studies have not accounted for sleep duration or school start time in this association, or examined a broad range of mental outcomes. In this study, we investigated the association between chronotype and mental health in a representative sample of adolescents from the 2014 Canadian Health Behaviour in School-Aged Children survey (29,635 students, 362 schools). We examined positive and negative aspects of mental health, using scores for emotional problems (range 0-33), emotional well-being (0-22), behavioural problems (0-28) and prosocial behaviours (0-25). We estimated chronotype using the time of mid-sleep on weekends and examined the associations using multilevel regressions, adjusted for sleep duration, school start time, individual, family and geographic characteristics. The average time of mid-sleep (chronotype) was 04:11 hr. An hour delay in mid-sleep time was associated with more emotional problems (0.34 [95% confidence interval 0.23, 0.45] point higher score), more behavioural problems (2.0% [95% confidence interval 1.4%, 2.6%] higher score), less emotional well-being (0.19 [95% confidence interval 0.09, 0.20] point lower score), and fewer prosocial behaviours (0.18 [95% confidence interval 0.08, 0.29] point lower score). A later chronotype was associated with poorer mental health, independent of sleep duration and school start time, and across internalizing and externalizing mental health domains. Further research is needed to clarify the mechanisms underlying this association. The timing of sleep, and not just its duration, may be an additional consideration for youth mental health.

The relationship between chronotype and mood fluctuation in the general population

There is a lack of evidence for the relationship between chronotype and subthreshold mood fluctuation. The present study aims to investigate the relationship between chronotypes and mood fluctuation in the general population. Participants (n=302) who have had no experience of major mood episodes were included. The Korean version of the Composite Scale of Morningness (CSM) was used to classify participants according to three chronotypes. Mood fluctuation was measured using the Mood Disorder Questionnaire (MDQ) and the Bipolar Spectrum Diagnostic Scale (BSDS). Mean scores achieved by the three chronotype groups on the MDQ and the BSDS were compared. There were no significant differences in the frequency of positive responses on the MDQ for the three chronotype groups. However, there was a significant group difference in total BSDS scores. The eveningness group had significantly higher BSDS-D scores than did either the morningness or the intermediate group have. In addition, the eveningness group had significantly higher BSDS-M scores than the morningness group. After adjusting for age by the analysis of covariance (ANCOVA), there were still significant group differences in total BSDS scores. The present results suggest that eveningness may be more related to mood fluctuation than morningness. The eveningness may be an important factor related to soft bipolarity or mood fluctuation.

The possible long-term effects of early-life circadian rhythm disturbance on social behavior

Sleep loss impairs brain function. As late sleep onset can reduce sleep, this sleep/circadian rhythm disturbance may cause brain impairment. Specific data on the long-term effects of sleep/circadian rhythm disturbance on subsequent brain function are lacking. Japan, a sleep-deprived society from infancy to adulthood, provides an ideal platform to investigate the association of these disturbances in early life with subsequent functioning. In this article, several current problematic behaviors among youth in Japan (dropping out from high school, school absenteeism, early resignation from employment, and suicide) are discussed in relation to early life sleep/circadian rhythm patterns. We hypothesize that daily habits of modern society during early stages of life produce unfavorable effects on brain function resulting in problematic behaviors in subsequent years.

Morningness-Eveningness in Adolescents

Individual morningness-eveningness differences explain the rhythmic variations of behavioral and biological patterns. Several studies have corroborated that morningness preference increases over adulthood and aging. Adolescents shift their time of day preferences from morningness to eveningness during puberty. The aims of this study were translate to Spanish the Morningness-Eveningness Scale for Children (MESC) and to analyze age and sex differences. A group of 600 adolescents (aged between 12 and 16 years) participated in the study. Psychometric analysis showed that reliability and factor structure were suitable and similar to previous studies. The results indicated a clear decrease of morningness as of 12 years. Boys were more morningness-oriented than girls in several items of the questionnaire. In view of the results, several educational implications are raised.

Adaptation of the Composite Scale of Morningness for Parent Report and Results from Kindergarten Children

Chronotype, or morningness-eveningness, refers to a person’s preference for a given time of day for intellectual and/or physical activities. It has many implications on health, well-being, performance, and daytime functioning. Because few data are available on prepubertal children, we assessed morningness-eveningness in kindergarten children using a parent-report scale, which was an adapted version of the Composite Scale of Morningness (CSM), and sleep-wake variables. A total of 199 parents of children from 15 kindergartens participated in the study. The CSM scores were relatively high, with a mean above 40 for all age groups, which clearly indicates that young children are early morning larks. Weekend wake-up times, rise times, bedtimes, and sleep-onset times were later than on weekdays. Sleep length did not differ in this respect, but time in bed was longer on weekends. Midpoint of sleep was earlier on weekdays. Wake times, rise times, bedtimes, and sleep-onset times were inversely correlated with the CSM score, suggesting that morning-oriented children woke up, got out of bed, went to bed, and fell asleep earlier than evening-oriented children. CSM scores correlated negatively with midpoint of sleep. Age correlated with CSM scores and midpoint of sleep.

Morningness: protective factor for sleep-related and emotional problems in childhood and adolescence?

The relationship between morningness/eveningness, sleep, and psychological problems is well documented in adults as well as in adolescents. However, research on the circadian orientation and its concomitants in younger children is scarce. The authors investigated the distribution of morningness/eveningness and its connection to sleeping and psychological problems in 91 children and 151 adolescents in Austria. The authors found that morning (M) types had less sleep-related and psychological problems than intermediate (I) and evening (E) types, respectively. Among children, M-types suffered less from daytime sleepiness (females: χ(2)((2)) = 8.1, p = .017; males: χ(2)((2)) = 14.8, p = .001). Among adolescents, M-types showed fewer sleep-wake problems (females: χ(2)((2)) = 17.5, p < .001; males: χ(2)((2)) = 19.8, p < .001), and female M-types showed less externalizing (χ(2)((2)) = 8.7, p = .013) as well as internalizing problem behavior (χ(2)((2)) = 9.0, p = .011). In conclusion, these findings indicate that morningness may act as a protective factor against the development of sleep-related problems in childhood and sleep-related and psychological problems in adolescence, especially in females.

Daily rhythms of the sleep-wake cycle

The amount and timing of sleep and sleep architecture (sleep stages) are determined by several factors, important among which are the environment, circadian rhythms and time awake. Separating the roles played by these factors requires specific protocols, including the constant routine and altered sleep-wake schedules. Results from such protocols have led to the discovery of the factors that determine the amounts and distribution of slow wave and rapid eye movement sleep as well as to the development of models to determine the amount and timing of sleep. One successful model postulates two processes. The first is process S, which is due to sleep pressure (and increases with time awake) and is attributed to a 'sleep homeostat'. Process S reverses during slow wave sleep (when it is called process S'). The second is process C, which shows a daily rhythm that is parallel to the rhythm of core temperature. Processes S and C combine approximately additively to determine the times of sleep onset and waking. The model has proved useful in describing normal sleep in adults. Current work aims to identify the detailed nature of processes S and C. The model can also be applied to circumstances when the sleep-wake cycle is different from the norm in some way. These circumstances include: those who are poor sleepers or short sleepers; the role an individual's chronotype (a measure of how the timing of the individual's preferred sleep-wake cycle compares with the average for a population); and changes in the sleep-wake cycle with age, particularly in adolescence and aging, since individuals tend to prefer to go to sleep later during adolescence and earlier in old age. In all circumstances, the evidence that sleep times and architecture are altered and the possible causes of these changes (including altered S, S' and C processes) are examined.

Sleep duration or bedtime? Exploring the relationship between sleep habits and weight status and activity patterns

STUDY OBJECTIVES

To assess the effects of early and late bedtimes and wake up times on use of time and weight status in Australian school-aged children.

DESIGN

Observational cross-sectional study involving use of time interviews and pedometers.

SETTING

Free-living Australian adolescents.

PARTICIPANTS

2200 9- to 16-year-olds from all states of Australia

INTERVENTIONS

NA.

MEASUREMENTS AND RESULTS

Bedtimes and wake times were adjusted for age and sex and classified as early or late using median splits. Adolescents were allocated into 4 sleep-wake pattern groups: Early-bed/Early-rise; Early-bed/Late-rise; Late-bed/Early-rise; Late-bed/Late-rise. The groups were compared for use of time (screen time, physical activity, and study-related time), sociodemographic characteristics, and weight status. Adolescents in the Late-bed/Late-rise category experienced 48 min/d more screen time and 27 min less moderate-to-vigorous physical activity (MVPA) (P<0.0001) than adolescents in the Early-bed/Early-rise category, in spite of similar sleep durations. Late-bed/Late-rise adolescents had a higher BMI z-score (0.66 vs. 0.45, P=0.0015). Late-bed/Late-rise adolescents were 1.47 times more likely to be overweight or obese than Early-bed/Early-rise adolescents, 2.16 times more likely to be obese, 1.77 times more likely to have low MVPA, and 2.92 times more likely to have high screen time. Late-bed/Late-rise adolescents were more likely to come from poorer households, to live in major cities, and have fewer siblings.

CONCLUSIONS

Late bedtimes and late wake up times are associated with an unfavorable activity and weight status profile, independent of age, sex, household income, geographical remoteness, and sleep duration.

An integrated effect of protein intake at breakfast and morning exposure to sunlight on the circadian typology in Japanese infants aged 2-6 years

Tryptophan (Trp) intake at breakfast promotes morning-typed circadian typology and higher sleep quality in Japanese children aged 0-6 yrs (Harada et al., 2007). This effect may be accelerated by morning exposure to sunlight, which has not yet been tested. This study aimed to investigate such an effect in Japanese children. In May, 2006, an integrated questionnaire was administered to 0-6-year-old children attending one of 12 kindergartens. 906 parents answered the questionnaire for their children and themselves (response rate: 67.4%). The integrated questionnaire included the revised version for children of the Morningness-Eveningness (M-E) Questionnaire and questions on sleep, nutritional balance, mental health, and sunlight exposure. Analysis was made on data from 744 children aged 2-6 (385 girls, 359 boys) whose average M-E score was 20.6+/-3.46. Children who had breakfast at regular times tended to be more morning-typed and were less frequently angry (p=0.001) and depressed (p=0.007). Children who had nutritionally well-balanced breakfasts tended to be more morning-typed (p<0.001), and woke up and fell asleep at earlier times (p<0.001). Children with higher protein intake tended to have higher M-E scores (p<0.001) and earlier bedtime and wake-up time (p=0.003). Children exposed to sunlight for 30-60 min on their way to kindergarten showed more distinctive shifting-effects to morning-type with protein intake than those exposed to sunlight for less than 20 min (p=0.006). A well-balanced breakfast might be a strong zeitgeber for circadian oscillators of children, and the morning-type driving effect of protein intake could be accelerated by morning exposure to sunlight.

Assessment of chronotype in four- to eleven-year-old children: reliability and validity of the Children's Chronotype Questionnaire (CCTQ)

Individual differences in circadian phase preference ("chronotype") are linked to sleep schedule variability, psychosocial functioning, and specific properties of the circadian clock. While much is known about the development, distribution, and variability of chronotype in adolescents and adults, assessment in prepubertal children has been hindered by a lack of appropriate, reliable, and valid measures. This study presents a detailed description of the assessment of children's chronotype by the Children's ChronoType Questionnaire (CCTQ). The CCTQ is a parent-report, 27-item mixed-format questionnaire resulting in multiple measures of chronotype in 4- to 11-yr-old children: the midsleep point on free days (MSF), a morningness/eveningness scale (M/E) score, and a five-point chronotype (CT) score. The study provides validity data using actigraphy as well as test-retest reliability data for all three chronotype measures and sleep/wake parameters. Overall, the findings indicate moderate to strong agreement between the three measures, adequate associations between chronotype measures and sleep/wake parameters assessed by actigraphy, and excellent temporal stability (reliability).

Validity of the Morningness‐Eveningness Scale for Children among Spanish Adolescents

Adolescents tend to be much later chronotypes than other age groups. This circadian phase delay is attributed as much to biological as psychosocial factors. Because the consequences of this change on performance and health have been documented, questionnaires to identify morning and evening-type adolescents are necessary. The aim of the present study was to validate a Spanish version of the Morningness-Eveningness Scale for Children (MESC) by means of several relevant psychological variables as external criteria. A sample of 623 urban high school students completed the MESC and self-reported measures of sleep behaviors, subjective alertness, physical performance, and mood. On the whole, results indicate a good validity of MESC. Significant differences in the self-reported ratings between morning and evening types were obtained by time-of-day. These results provide preliminary support for the Spanish version of MESC.

Association Between Moringness‐Eveningness Preference and Mental/Physical Premenstrual Symptoms in Japanese Females 12 to 31 Years of Age

This study investigates the relationship between circadian typology, i.e., morningness-eveningness (M-E) preference, and the occurrence and severity of premenstrual mental and physical symptoms among 154 young Japanese female university students (range, 18 to 31 yrs; mean+/-S.D., 20.69+/-3.69 yrs) and 417 junior high school students (range, 12 to 15 yrs; mean+/-S.D., 14.29+/-0.67 yrs) living in an urban or suburban area of Kochi prefecture. Female university students experienced melancholy mood more frequently than did males, and the female university students who frequently became melancholy were more evening-typed than those who did not experience melancholy. Female university students who experienced frequent fluctuations in mood and/or menstrual pain were more evening-typed than those who were not so affected. M-E preference of junior high school students was not correlated with stability of mood or frequency of menstrual pain. In urban areas, however junior high school students who had very stable menstrual cycles were significantly more morning-typed than those whose menstrual cycles were not stable. In suburban areas, the bedtimes of female junior high students who had stable menstrual cycles were significantly earlier than those whose menstrual cycle duration was not stable. A physiological relationship between the circadian system, M-E, and attributes of the menstrual cycle seems to be present in adolescent female Japanese junior high school students.

Morning‐Evening Preference: Sleep Pattern Spectrum and Lifestyle Habits Among Japanese Junior High School Pupils

We surveyed the sleep-wake patterns and lifestyle habits in a sample of Japanese first to third year junior high school children (n=638, age 12 to 15 yrs), of whom 29.3% were evening type, 64.1% intermediate type, and 6.6% morning type in preference. The morningness-eveningness (M-E) score was lower (more evening typed), 16.1 vs. 15.4 in first compared to third year students. There were significant gender differences, with girls showing a greater evening preference. Evening preference was associated with longer sleep latency, shortened sleep duration during schooldays and weekends, bad morning feeling, and episodes of daytime sleepiness. In contrast, morning preference was associated with higher sleep drive and better sleep-wake parameters and lifestyle habits. Our results suggest the morning preference should be promoted among junior high school children to increase the likelihood of more regular sleep-wake patterns and lifestyle habits.