Chronotype, sleep length, and school achievement of 11- to 23-year-old students in northern European Russia

Greater social jetlag predicts poorer NIH Toolbox crystallized cognitive and academic performance in the Adolescent Brain Cognitive Development (ABCD) study

Academic performance plays a crucial role in long-term educational attainment and occupational function. Chronotype refers to an individual's daily tendencies for times for waking, activity, and sleep. Social jetlag reflects the mismatch between an individual's chronotype and their social schedule. Because school typically starts early in the morning, later chronotype is often associated with daytime sleepiness, insufficient sleep, and poor academic performance. However, the relationship between academic performance, chronotype, and social jetlag has not been extensively examined in large samples like the Adolescent Brain Cognitive Development (ABCD) study. We hypothesized that greater social jetlag would predict poorer cognitive and academic performance. Year 2 (ages 11-14) cross-sectional data from the ABCD cohort (n = 6,890 adolescents) were used to evaluate academic performance (i.e. self-reported past year grades), NIH Toolbox cognitive performance measures, chronotype, and social jetlag from the Munich Chronotype Questionnaire. We found that later chronotype and greater social jetlag predicted poorer cognitive and academic performance with small effect sizes. Our findings emphasize the importance of individual differences in chronotype and social jetlag when designing class schedules, as aligning school activities with student optimal sleep-wake times may contribute to improved academic performance.

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.

Circadian preference and physical and cognitive performance in adolescence: A scoping review

Adolescence is a crucial period of development which coincides with changes in circadian rhythmicity. This may augment the impact of circadian preference on performance in this group. We aimed to scope the literature available on chronotypes and their effect on physical and mental aspects of performance in adolescents. Studies were identified by systematically searching bibliographical databases and grey literature. The Morningness-Eveningness Questionnaire was the most frequently reported tool for circadian preference assessment. Academic achievement was the most prevailing outcome, with evidence suggesting that morning type adolescents tend to outperform evening types, yet the results vary depending on multiple factors. Performance in tests of intelligence and executive functions was generally better at optimal times of the day (synchrony effect). Physical performance was examined in 8 studies, with very heterogeneous outcomes. Although the associations between circadian preference and performance in adolescents are evident in some areas, there are many factors that may be involved in the relationship and require further investigation. This review highlights the assessment of physical performance in relation to chronotypes, the multidimensional assessment of circadian preference, and the need for longitudinal studies as priorities for further research.Protocol: OSF Registration - Public registration, DOI: 10.17605/OSF.IO/UCA3Z.

Chronotype and lipid metabolism in Arctic Sojourn Workers

This study relates answers to the Munich Chronotype Questionnaire (MCTQ) and Pittsburgh Sleep Quality Index (PSQI) from Arctic Sojourn Workers (ASW) of Yamburg Settlement, 68° Latitude North, 75° Longitude East (n = 180; mean age ± SD; range: 49.2 ± 7.8; 25-66 y; 45% women) to Arctic Sojourn Work Experience (ASWE), age and health status. Chronotype, Mid Sleep on Free Days sleep corrected (MSFsc) and sleep characteristics of ASW were compared to those of age-matched Tyumen Residents (TR, n = 270; mean age ± SD; range: 48.4 ± 8.4; 25-69 y; 48% women), 57° Latitude North, 65° Longitude East. ASW have earlier MSFsc than TR (70 min in men, p < 0.0001, and 45 min in women, p < 0.0001). Unlike TR, their MSFsc was not associated with age (r = 0.037; p = 0.627) and was linked to a larger Social Jet Lag (+21 min in men; p = 0.003, and +18 min in women; p = 0.003). These differences were not due to outdoor light exposure (OLE): OLE on work (OLEw) or free (OLEf) days was not significantly different between ASW and TR in men and was significantly less in ASW than in TR women (OLEw: -31 min; p < 0.001; OLEf: -24 min; p = 0.036). ASWE, but not age, was associated with compromised lipid metabolism in men. After accounting for multiple testing, when corrected for age and sex, higher triglycerides to high-density lipoprotein ratio, TG/HDL correlated with ASWE (r = 0.271, p < 0.05). In men, greater SJL was associated with lower HDL (r = -0.204; p = 0.043). Worse proxies of metabolic health were related to unfavorable components of the Pittsburgh Sleep Quality Index in ASW. Higher OLE on free days was associated with lower systolic (b = -0.210; p < 0.05) and diastolic (b = -0.240; p < 0.05) blood pressure.

The influence of a permanent double-shift school start time on adolescent sleep and chronotype across different age groups

The main objective of this study was to explore the differences in sleep habits and chronotype across different age groups in Mexican adolescents attending a permanent double-shift school system. This cross-sectional study consisted of 1,969 (1,084 girls) students from public elementary, secondary, and high schools, as well as undergraduate university students from Mexico. Age range was 10-22 [15.33 ± 3.28 (mean ± SD)] years, 988 morning shift and 981 afternoon shift students. Questions regarding usual self-reported bedtime and rise time were collected, and from that, estimates for time in bed, midpoint of sleep, social jetlag, and chronotype were evaluated. Afternoon shift students reported later rise times, bedtimes, midpoint of sleep, and longer time in bed on school days than morning shift students, as well as less social jetlag. Overall, afternoon shift students reported a later chronotype than morning shift students. Peak lateness of chronotype in afternoon shift students was at age 15, with girls peaking at age 14 and boys at age 15. Meanwhile, morning shift students reported peak lateness of chronotype around age 20. In this study, adolescents from different age ranges attending an extremely delayed school start time reported adequate sleep compared with adolescents attending a fixed morning school start time. In addition, the analysis presented in this study seems to suggest that the peak of late chronotype may be influenced by school start times.

Sleep Quality and Social Jetlag in Young Adults During the Social Distancing Caused by COVID-19

Introduction:  This study aimed to evaluate the sleep quality and the Social Jetlag frequency in young adults during social distancing because of COVID-19. Methods:  This is a cross-sectional study with 308 students aged ≥18 years and with Internet access. Questionnaires used: Pittsburgh Sleep Quality Index - Brazil (PSQI-BR), Epworth Sleepiness Scale, and Munich Chronotype Questionnaire. Results:  The mean age of the students was 21 ± 3 years (17 - 42y), with no statistically significant difference between genders. The PSQI-BR indicated that 257 (83.4%) had poor sleep quality. The mean of Social Jetlag for young adults was 02:00 ± 01:49h, and we observed that 16.6% (n = 51) had Social Jetlag. Compared to men in the good sleep quality group, women had higher means for sleep duration on study days and free days, mid-point of sleep on study days and free days and corrected mid-point of sleep on free days. However, when compared to men in the group of poor sleep quality, we observed higher means for women regarding sleep duration on study days, the mid-point of sleep on study days, and the corrected mid-point of sleep on free days. Conclusions:  Thus, the high frequency of young adult students who had poor sleep quality associated with Social Jetlag (2 hours) in the present study may reflect a pattern of sleep irregularity, which may be associated with impairment of environmental synchronizers and stimulation of social synchronizers during the lockdown resulting from the COVID-19 pandemic.

Chronotype at the beginning of secondary school and school timing are both associated with chronotype development during adolescence

The misalignment between late chronotypes and early school start times affect health, performance and psychological well-being of adolescents. Here we test whether, and how, the baseline chronotype (i.e. chronotype at the beginning of secondary school) and the school timing affect the magnitude and the direction of the developmental change in chronotype during adolescence. We evaluated a sample of Argentinian students (n = 259) who were randomly assigned to attend school in the morning (07:45 a.m.–12:05 p.m.), afternoon (12:40 p.m.–05:00 p.m.) or evening (05:20 p.m.–09:40 p.m.) school timings. Importantly, chronotype and sleep habits were assessed longitudinally in the same group of students along secondary school (at 13–14 y.o. and 17–18 y.o.). Our results show that: (1) although chronotypes partially align with class time, this effect is insufficient to fully account for the differences observed in sleep-related variables between school timings; (2) both school timing and baseline chronotype are independently associated with the direction and the magnitude of change in chronotype, with greater delays related to earlier baseline chronotypes and later school timings. The practical implications of these results are challenging and should be considered in the design of future educational timing policies to improve adolescents’ well-being.

The Relationship Between Circadian Typology and Dry Eye Symptoms in Chinese College Students

PURPOSE

To explore the relationship between symptomatic dry eye and circadian typology in college students.

METHODS

This study included 269 students from 3 Chinese universities. All participants completed the ocular surface disease index (OSDI) questionnaire, the morningness-eveningness questionnaire (MEQ), and the Pittsburgh sleep quality index (PSQI) questionnaire. Participants were grouped into 3 types by the reduced MEQ (rMEQ) score:E-Type, N-Type, and M-Type. All these parameters were then analyzed for the effect on the severity of dry eye.

RESULTS

The occurrence rates of poor sleep quality (PSQI>5) and symptomatic dry eye (OSDI > 13) in the college students were 53.2% and 40.2%, respectively. The distribution of the circadian typology differed significantly among the college students with different dry eye severities (χ ² = 59.44, P = 0. 000), and E-type was associated with the most severe dry eye symptoms. The OSDI and PSQI scores were both significantly different among college students with different chronotypes (F = 22.14, P = 0.000; F = 15.21, P = 0.000; respectively). For both scores, the E-type scored the highest, followed by N-type, and M-type was the lowest. The circadian typology was an independent factor for dry eye. The risk of E-Type was 6.99 times higher than that of M-Type (P = 0.000), and the risk of N-types was 3.23 times higher than that of M-Type (P = 0.000). Sleep quality was also an independent risk factor for dry eye (P = 0.000). Gender and awareness of dry eye were not risk factors for dry eye.

CONCLUSION

The severity of dry eye symptoms and sleep quality were associated with different circadian typologies. The more the circadian preference tended to be E-type, the worse the sleep quality and the more serious dry eye symptoms would appear.

The multiplicative effect of stress and sleep on academic cognitions in Latino college students

Latino students are increasingly represented in higher education within the United States, but remain one of the groups least likely to graduate from a four-year institution. Stress and sleep are factors that have been implicated in students' academic success. This study examined concurrent and longitudinal interactive effects of stress and sleep on academic cognitions in a sample of 196 Latino students (M_age = 18.95; 64.4% female) in their second and third semester of college. Stress and actigraphy-measured sleep (duration, efficiency, midpoint, midpoint-variability) were measured in the second semester and academic cognitions (engagement, motivation, self-efficacy) were measured in the second and third semesters. Structural equation modeling revealed that higher stress was concurrently related to lower academic cognitions for students with consistently delayed sleep timings (e.g., later average midpoints) and longitudinally related to reduced academic functioning for students with lower sleep efficiency. These findings can inform programs that target stress-reduction and sleep hygiene among incoming college students.

Chronotype, sleep quality and academic performances among Mizo students

Sleep is an essential component of the daily cycle. Age and puberty-related declines in sleep duration, delays in chronotype, and an increase in social jet lag have been consistently reported. This study examined chronotype and gender-based differences in adolescents' sleep quality, depression level, and academic achievements. Eight hundred fifteen school students (372 male and 443 female) aged 14 to 20 years voluntarily participated in this study. Horne and Östberg Morningness-Eveningness Questionnaire (MEQ) was used to measure their chronotype. Sleep duration, sleep quality, and daytime sleepiness were assessed by the Pediatric Daytime Sleepiness Scale (PDSS) and Epworth Sleepiness Scale (ESS). Pittsburgh's Sleep Quality Index (PSQI) was used to evaluate sleep habits. Cleveland Adolescent Sleepiness Questionnaire (CASQ) was used to measure the sleep pattern of the students. Zung Self-Rating Depression Scale (SDS) was used to assess the level of depression for the students. Our results show neither type of students dominated the population studied but interestingly, in comparison to evening type, morning type individuals were higher among the population. Chronotype-based sleep quality and academic performances were observed, and higher depression levels, poor sleep quality, poor academic performances were observed in evening type compared to neither type and morning type. In contrast to males, females had a poor sleep pattern (CASQ) and a higher depression level (SDS). Altogether, our study shows the effect of chronotype and gender on sleep quality and depression levels among school students.

Chronotypes in the US: Influence of longitude position in a time zone

The availability of electrical light has altered modern light exposure, affecting the synchronization process ('entrainment') of the circadian clock to the natural light-dark cycle. The discrepancy between the natural light-dark cycle and self-selected light exposure has raised the question whether humans entrain to sun time (as most organisms do) vs. social time. None of the studies addressing this question have been conducted in the US in a large-scale, nationally representative sample. In this brief report, we aimed at estimating the relationship between individual chronotype (the result of the entrainment process) and longitude position in a time zone, using 12 years (2003-2014) of pooled diary data (n = 50,753) from the American Time Use Survey (ATUS). Chronotype was estimated based on mid-sleep time on weekends (MSF^We), a proxy that was previously shown to replicate known age and sex differences in chronotype in the ATUS. Longitude position was derived from state-level information (e.g., average state border outline). Regression results showed a progressive delay in MSF^We from east to west within three of the four US continental time zones (delay per degree of longitude): Eastern, 1.8 min; Central, 1.2 min; Mountain, 2.4 min (all p < .01). The findings suggest that humans entrain to sun time, leading to an increasing discrepancy between social time and biological time ("circadian misalignment") towards the west of a time zone. Such a misalignment induced by where people live within a time zone may affect a large share of the population, with implications for health and safety.

Circadian preference and academic achievement in school-aged students: a systematic review and a longitudinal investigation of reciprocal relations

We provide a systematic review of findings on the relation between circadian preference and school achievement published after the last comprehensive review in 2015. We further test this relation in a longitudinal study. Our review of 26 studies revealed a positive relation between morningness and students' school achievement, and a negative relation between eveningness and school achievement. In most studies, these relations were not affected by students' age, sex, or intelligence, but were significantly mediated by students' conscientiousness, motivation, and sleep behavior. Furthermore, circadian preference and school achievement showed no significant relation when school started in the afternoon. All studies were cross-sectional. Therefore, the direction of the relations between circadian preference, school achievement, and potential mediating variables like conscientiousness and motivation could not be investigated. In our longitudinal study, we tested the direction of the relations between circadian preference, academic achievement, conscientiousness, self-efficacy, and attitude toward school over time in a sample of 764 German high school students who were tested in the first (T1) and third (T2) year of high school. Findings from confirmatory cross-lagged models indicated reciprocal relations between circadian preference and school achievement: T1 morningness positively predicted change in grade point average over time while T1 grade point average positively predicted change in morningness and negatively predicted change in eveningness. Furthermore, T1 conscientiousness and T1 attitude toward school both positively predicted change in morningness, whereas T1 morningness and T1 eveningness did not significantly predict change in these variables.

Biological Rhythm and Chronotype: New Perspectives in Health

The circadian rhythm plays a fundamental role in regulating biological functions, including sleep–wake preference, body temperature, hormonal secretion, food intake, and cognitive and physical performance. Alterations in circadian rhythm can lead to chronic disease and impaired sleep. The circadian rhythmicity in human beings is represented by a complex phenotype. Indeed, over a 24-h period, a person’s preferred time to be more active or to sleep can be expressed in the concept of morningness–eveningness. Three chronotypes are distinguished: Morning, Neither, and Evening-types. Interindividual differences in chronotypes need to be considered to reduce the negative effects of circadian disruptions on health. In the present review, we examine the bi-directional influences of the rest–activity circadian rhythm and sleep–wake cycle in chronic pathologies and disorders. We analyze the concept and the main characteristics of the three chronotypes.

Test Anxiety and Poor Sleep: A Vicious Cycle

BACKGROUND

Test anxiety may be better thought of as a biopsychosocial process affecting academic performance during the days leading up to an exam, rather than a static appraisal of attitudes related to test taking. This was a passive observational study following students 2 days before a midterm exam and was designed to test the Sleep Anxiety Performance Process (SAPP) model in the context of a psychology statistics exam.

METHODS

Undergraduates (N = 167) enrolled in a statistics class, January-November 2015. Participants completed an electronic battery of measures and Sleep Mood Study Diaries (SMS) during the mornings, 2 days before a statistics exam. Instructors confirmed exam scores.

RESULTS

A path model showed a reciprocal bi-directional relationship between Sleep Quality and restfulness (Q&R) and test anxiety 2 days before a scheduled exam, with test anxiety measured in the morning, before the exam predicting exam performance. Prior exam performance, being a non-native English speaker (ESL), and class performance motivation also predicted exam performance.

CONCLUSIONS

These data support the SAPP model's premise that that sleep and anxiety feed one another, as a reciprocal process, that collectively impairs academic performance, with direct effects on academic performance, but with implications for overall student health.

Should I study or should I go (to sleep)? The influence of test schedule on the sleep behavior of undergraduates and its association with performance

Sleep is crucial for college students' well-being. Although recommended sleep duration is between 7-9 hours per day, many students do not sleep that much. Scholar demands are among the causes of observed sleep deprivation in youth. We explored the influence of having a school test on previous night sleep in first-year students and the association of sleep duration and test performance. We ran two surveys in freshman students of the Universidad de la República, Montevideo, Uruguay: 1) 97 students of the School of Sciences who took the test at the same time; and 2) 252 School of Psychology students who took the test in four successive shifts. More than 1/2 of the participants (survey #1) and almost 1/3 (survey #2) reported short regular sleep duration (< 7h). In both samples, the sleep duration of the night before the test was reduced with respect to regular nights (survey #1: 2.1 ± 0.2 h, p < 0.001; survey #2: between 1.7 ± 0.4 h and 3.6 ± 0.3 h, all p < 0.001), with more than 10% of the students who did not sleep at all. In survey 2, sleep duration increased in later shifts (F (3,248) = 4.6, p = 0.004). Using logit regressions, we confirmed that sleep duration was positively related to test scores in both samples (survey #1: exp B = 1.15, p < 0.001; pseudo-R2 = 0.38; survey #2: exp B = 1.03, p < 0.001; pseudo-R2 = 0.25). Delaying test start time may prevent the reduction in sleep duration, which may also improve school performance. In addition, educational policies should include information for students about the impact of sleep on learning and of the consequences of reduced sleep duration.

Social Jetlag and Excessive Daytime Sleepiness from a Sample of Russian Children and Adolescents

PURPOSE

Insufficient nocturnal sleep is a primary source of excessive daytime sleepiness. Most previous research has focused on the disparity between sleep demands and study start times in adolescents. Fewer studies have focused on elementary schoolchildren. We hypothesize that late sleep timing is connected to excessive daytime sleepiness in a sample of Russian children and adolescents. The major goals of our study were to evaluate excessive daytime sleepiness in Russian schoolchildren and adolescents using the Russian version of the Pediatric Daytime Sleepiness Scale (PDSS) and to estimate its relationship with sleep-wake parameters using the Munich Chronotype Questionnaire (MCTQ).

MATERIALS AND METHODS

Student subjects were from public educational facilities in the Republic of Karelia. They completed both the PDSS and the Munich Chronotype Questionnaire to estimate sleep parameters and chronotype (MSFsc). Five hundred and eleven students provided data for the PDSS and sleep-wake variables, and 479 for the full MCTQ data.

RESULTS

The overall prevalence of Excessive Daytime Sleepiness (EDS) in our sample was 18%. The total PDSS score was inversely correlated with sleep length on school nights and was independent of respondents' sex. Higher PDSS scores were associated with later bedtimes on school days and free days, and shorter sleep duration on school days. Late chronotype and more pronounced social jetlag were both positively correlated with high PDSS scores. A negative correlation was found between chronotype and the duration of the sleep period on weekdays (p < 0.001) and a positive correlation was found on weekends (p < 0.001). Longer average sleep duration was positively related to less daytime sleepiness.

CONCLUSION

This study suggests that excessive daytime sleepiness is chronotype-dependent. School start times could be shifted to a later hour to prolong sleep and reduce EDS.

Narrow-band ultraviolet B (NB UV-B) exposures improve mood in healthy individuals differently depending on chronotype

The evening chronotype is associated with psychological symptoms such as depressed mood, while skin exposure to ultraviolet radiation (UVR) may affect mood and behavior through neural and humoral routes. This pilot study aimed to investigate the impact of whole-body narrow-band (NB) UV-B exposure on current mood state and circulating 25-hydroxyvitamin D3 (25(OH)D₃), interleukin-6 (IL-6), cortisol and β-endorphin (β-END) levels in healthy participants. Here, eleven healthy women received full-body NB UV-B exposures on four afternoons, and the chronotype was assessed with a shortened version of Horne and Östberg's Morningness-Eveningness Questionnaire (MEQ). Perceived mood was evaluated using the Visual Analogue Scale (VAS), and serum 25(OH)D₃, IL-6, cortisol and β-END concentrations were monitored daily. Decreasing VAS values showed mood to improve significantly over the five days after the four suberythematous NB UV-B exposures (p = .038), and the more the circadian preference was inclined toward eveningness, the greater the improvement in the mood dimension of wellbeing (p = .021). Baseline mood state was correlated with baseline 25(OH)D₃ (r = -0.54, 95% CI: -0.86 to -0.09) and with baseline cortisol (r = -0.57, 95% CI: -0.87 to -0.04). During the NB UV-B exposures, 25(OH)D₃ increased significantly, as expected, and IL-6 declined significantly by -0.35 (95% CI: -0.69 to -0.07) pg/mL from the initial values of 1.12 ± 0.66 pg/mL (p = .025). In conclusion, in our pilot study, NB UV-B exposure improved mood, especially among those with evening preference for their daily activities, as well as circulating 25(OH)D₃ levels, whereas circulating IL-6 levels decreased. Abbreviations: UVR: Ultraviolet radiation; NB UV-B: narrow-band UV-B; VAS: Visual Analogue Scales; β-END: β-endorphin; IL-6: Interleukin-6.

Effect of chronotype on academic achievement in a sample of Italian University students

Circadian rhythms play an important role in biological function; their expression differs across individuals; three chronotypes are distinguished: Morning- [MT], Evening- [ET], and Neither- [NT] type. MT achieve peak activation in the first part of the day and are generally more conscientious and achievement-oriented than ET, which reach their best during the second half of the day and express a higher intelligence. University class schedules can sometimes conflict with ET circadian preferences, compromising their academic performance compared with their MT classmates. Conversely, MT students, being more aligned with their daily schedule, might be more advantaged in their mental performance. The attitudes and performance of NT students are little considered. No studies to date have investigated academic achievement in relation to chronotype in an Italian student population. To fill this gap, this study examined the relationship between chronotype and academic performance in a population of Motor Science Faculty in Milan, differentiating achievement in theoretical and practical subjects by chronotype. The study population was 423 university students (290 males and 133 females) and categorized by chronotype according to Morningness-Eveningness Questionnaire (MEQ) scores. Student transcripts were reviewed to obtain exam grades on three practical and three theoretical subjects. The interaction between MEQ score or chronotypes and mean exam grade was evaluated using one-way ANOVA. The mean grades on the theoretical and practical exams were higher for the MT than for either the ET or the NT students. The NT students (24.8 ± 0.1) had lower mean grades for the theoretical subjects than either the MT (26.3 ± 0.4) or the ET (25.3 ± 0.2) students, while the ET (26.6 ± 0.2) performed worse than either the MT (27.8 ± 0.2) or the NT students (26.9 ± 0.1) on the practical exams. The same trend was observed for the total sample and when subdivided by sex. In the total sample, significant differences in theoretical and practical exam grades were noted between chronotypes: MT vs ET (p < .002, p < .0006) and MT vs NT (p < .04, p < .003). The differences between the males were significant for the theoretical (p < .006, MT vs NT, p < .002) and the practical subjects (MT vs ET p < .004, MT vs NT, p < .01), but no significant differences were noted between the females. Our findings indicate overall better academic achievement by the MT students, whereas the NT had lower exam grades for the theoretical subjects and the ET performed worse on the practical exams. We speculate that the higher intelligence expressed by the ET students might have helped them compensate the disadvantage on the theoretical but not on practical exams, in which the effect of misalignment between circadian preferences and university class schedule was more evident.

Psychometric properties of the Russian version of the Pediatric Daytime Sleepiness Scale (PDSS)

Insufficient sleep could severely impair both cognitive and learning skills. More prominent changes are found in children and adolescents. Tools used to estimate sleepiness in the adult population are commonly inappropriate for children. The objective of our study was to provide a reliable instrument to measure excessive sleepiness for upcoming studies in Russian-speaking children, applying the Russian version of Pediatric Daytime Sleepiness Scale (PDSS). The following tasks were resolved in our study: translation, validation, and analysis of psychometric properties of the Russian adaptation of the PDSS by standard tests. After the semantic validation of the instrument through a multi-stage translation process we checked its psychometric validation. A total of 552 students, consisting of N = 285 for the exploratory factor analysis (EFA), N = 267 for the confirmatory factor analysis (CFA) and N = 204 for test-retest analysis of public elementary schools located in Northern Russia completed the PDSS and Munich Chronotype Questionnaire to estimate sleep parameters in the classroom during the lessons. Response rate was 90%; excluded cases contained no data. Further, 204 of our participants completed the PDSS in a 3 months interval to check the test-retest reliability. Internal consistency was measured by Cronbach's alpha coefficients and CFA was used to test factorial validity of the tool. Concurrent validity and test-retest reliability were assessed via intra-class coefficient. Internal consistency of the PDSS scale was high (Cronbach's α = 0.8). The construct validity of the PDSS was supported by CFA (factor loadings were from 0.438 to 0.727) and the test-retest reliability demonstrated by the intra-class coefficient was 0.70. The total PDSS score was independent of sex. The mean total value of PDSS was 11.95 ± 6.24. Higher scores on PDSS were negatively correlated with sleep duration. Thus, the construct validity of the instrument remains valid and could be used for Russian-speaking youth samples in the evaluation of daytime sleepiness. It could be useful in future applications by sleep scientists and health practitioners.

Chronotype and Social Jetlag: A (Self-) Critical Review

The Munich ChronoType Questionnaire (MCTQ) has now been available for more than 15 years and its original publication has been cited 1240 times (Google Scholar, May 2019). Additionally, its online version, which was available until July 2017, produced almost 300,000 entries from all over the world (MCTQ database). The MCTQ has gone through several versions, has been translated into 13 languages, and has been validated against other more objective measures of daily timing in several independent studies. Besides being used as a method to correlate circadian features of human biology with other factors-ranging from health issues to geographical factors-the MCTQ gave rise to the quantification of old wisdoms, like "teenagers are late", and has produced new concepts, like social jetlag. Some like the MCTQ's simplicity and some view it critically. Therefore, it is time to present a self-critical view on the MCTQ, to address some misunderstandings, and give some definitions of the MCTQ-derived chronotype and the concept of social jetlag.

[Sleep quality and its parameters in schoolchildren]

AIM

Sleep disorders are very common among teenagers. One of possible reasons is a discrepancy between social and biological activity of children. It is known that adolescents with a late chronotype (e.g., a later midpoint of sleep) have a lowered academic achievement. The aim of our study was to evaluate sleep quality and other sleep-wake characteristics in relation to academic scores self-reported by teenagers living in urban and rural areas of Republic of Karelia.

MATERIAL AND METHODS

Five hundred respondents, aged 10-17 years, participated in a questionnaire survey of chronotype and sleep quality. The Munich chronotype questionnaire (MCTQ) and the Pittsburgh Sleep Quality Index (PSQI) were used. Sleep duration during week and weekend, sleep quality and hygiene were assessed.

RESULTS AND CONCLUSION

A decrease in sleep duration in adolescents, aged 10-18 years, was observed. A larger social jetlag was significantly higher in girls compared to boys. Gender had a significant impact on sleep quality. More than 10% of the total variation in academic achievement of Karelian teenagers can be explained by the difference in their gender and average sleep duration.

Epidemiology of objectively measured bedtime and chronotype in US adolescents and adults: NHANES 2003-2006

BACKGROUND

We propose a method for estimating the timing of in-bed intervals using objective data in a large representative US sample, and quantify the association between these intervals and age, sex, and day of the week.

METHODS

The study included 11,951 participants 6 years and older from the National Health and Nutrition Examination Survey (NHANES) 2003-2006, who wore accelerometers to measure physical activity for seven consecutive days. Participants were instructed to remove the device just before the nighttime sleep period and put it back on immediately after. This nighttime period of non-wear was defined in this paper as the objective bedtime (OBT), an objectively estimated record of the in-bed interval. For each night of the week, we estimated two measures: the duration of the OBT (OBT-D) and, as a measure of the chronotype, the midpoint of the OBT (OBT-M). We estimated day-of-the-week-specific OBT-D and OBT-M using gender-specific population percentile curves. Differences in OBT-M (chronotype) and OBT-D (the amount of time spent in bed) by age and sex were estimated using regression models.

RESULTS

The estimates of OBT-M and their differences among age groups were consistent with the estimates of chronotype obtained via self-report in European populations. The average OBT-M varied significantly by age, while OBT-D was less variable with age. In the reference group (females, aged 17-22 years), the average OBT-M across 7 days was 4:19 AM (SD = 30 min) and the average OBT-D was 9 h 19 min (SD = 12 min). In the same age group the average OBT-D was 18 minutes shorter for males than for females, while the average OBT-M was not significantly different between males and females. The most pronounced differences were observed between OBT-M of weekday and weekend nights. In the reference group, compared to the average OBT-M of 3:50 am on Monday through Thursday nights, there was a 57-minute delay in OBT-M on Friday nights (entering the weekend), a 69-minute delay on Saturday nights (staying in the weekend), and a 23-minute delay on Sunday night (leaving the weekend). For both OBT-M and OBT-D, in most age groups and for most days of the week, there were no statistically significant differences between males and females, except for OBT-D on Wednesdays and Thursdays, with males having 31 (p-value < 0.05) and 45 (p-value < 0.05) minutes shorter OBT-D, respectively.

CONCLUSIONS

The proposed measures, OBT-D and OBT-M, provide useful information of time in bed and chronotype in NHANES 2003-2006. They identify within-week patterns of bedtime and can be used to study associations between the bedtime and the large number of health outcomes collected in NHANES 2003-2006.

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).

Latitudinal cline of chronotype

The rotation of the Earth around its own axis and around the sun determines the characteristics of the light/dark cycle, the most stable and ancient 24 h temporal cue for all organisms. Due to the tilt in the earth’s axis in relation to the plane of the earth’s orbit around the sun, sunlight reaches the Earth differentially depending on the latitude. The timing of circadian rhythms varies among individuals of a given population and biological and environmental factors underlie this variability. In the present study, we tested the hypothesis that latitude is associated to the regulation of circadian rhythm in humans. We have studied chronotype profiles across latitudinal cline from around 0° to 32° South in Brazil in a sample of 12,884 volunteers living in the same time zone. The analysis of the results revealed that humans are sensitive to the different sunlight signals tied to differences in latitude, resulting in a morning to evening latitudinal cline of chronotypes towards higher latitudes.

Lower school performance in late chronotypes: underlying factors and mechanisms

Success at school determines future career opportunities. We described a time-of-day specific disparity in school performance between early and late chronotypes. Several studies showed that students with a late chronotype and short sleep duration obtain lower grades, suggesting that early school starting times handicap their performance. How chronotype, sleep duration, and time of day impact school performance is not clear. At a Dutch high school, we collected 40,890 grades obtained in a variety of school subjects over an entire school year. We found that the strength of the effect of chronotype on grades was similar to that of absenteeism, and that late chronotypes were more often absent. The difference in grades between the earliest 20% and the latest 20% of chronotypes corresponds to a drop from the 55^th to 43^rd percentile of grades. In academic subjects using mainly fluid cognition (scientific subjects), the correlation with grades and chronotype was significant while subjects relying on crystallised intelligence (humanistic/linguistic) showed no correlation with chronotype. Based on these and previous results, we can expand our earlier findings concerning exam times: students with a late chronotype are at a disadvantage in exams on scientific subjects, and when they are examined early in the day.

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.

Latitude affects Morningness-Eveningness: evidence for the environment hypothesis based on a systematic review

Morningness-eveningness (M/E) is an individual trait related to a person’s sleep-wake cycle and preference for morning or evening hours. The “environment hypothesis” suggests that M/E is dependent on environmental factors, such as latitude, mean average temperature and photoperiod. We here analyzed a large number of datasets to assess this effect based on a systematic review. Data were from a total of 87 datasets and 35,589 individuals based on 28 countries. Partial correlations correcting for age revealed significant relationships between M/E and latitude, mean yearly temperature, photoperiod and sunset. Evening orientation was related to higher latitude, longer days and later sunset. Morning orientation was related to higher average temperatures. Percentage of females and sunrise time had no significant influence. These variables (sunset, temperature, photoperiod) were then input in a general linear model. The full model showed an influence of age and of sunset on CSM scores, but not of photoperiod and average temperature. Sunset, therefore, seems to be the most important statistical predictor for the observed latitudinal gradient.

The association between chronotype and perceived academic stress to depression in medical students

Depression is a multifactorial illness that is highly prevalent among medical students (MS). Chronotypes, which reflect circadian preference in humans, as well as academic stress have been associated with depression in different populations. However, it is not known how chronotype and stress might alone or in combination, associate with depression in MS. Thus, we aimed to evaluate the association between stress, chronotype and depression in MS. In a cross-sectional study, we evaluated a total of 1068 medical students from a public Medical School in Mexico City. The Patient Health Questionnaire-9 (PHQ-9) was used to evaluate depressive symptom severity and the presence of a current depressive episode with a cutoff score of 10 or higher. The Morning-Evening Questionnaire (MEQ) was used to establish chronotype and the Academic Stress Inventory was used to measure perceived academic stress (PAS). We observed that depressive symptom severity was higher in non-morning chronotypes and moderate/severe PAS groups. A factorial ANOVA showed an association between PAS groups and depressive symptom severity. Linear regression showed an association between depressive symptom severity and variables such as PAS scores (p = 0.001), family history of depression (p = 0.001), gender (p = 0.001) and academic year (p = 0.029). Logistic regression analysis showed that evening chronotype (OR: 2.3, 95% CI: 1.2-4.3, p = 0.01) and severe PAS (OR: 4.4, 95% CI: 2.8-7.0, p = 0.0001) were associated with depression. Further, MS with the combination of severe PAS and morning (OR: 5.9, 95% CI: 1.6-22.2, p = 0.01), intermediate (OR: 7.5, 95% CI: 2.3-24.4, p = 0.001) or evening (OR: 10.6, 95% CI: 2.8-40.0, p = 0.001) chronotypes showed a greater association with depression than any PAS or chronotype group alone. Being female, perceiving restricted or limited economic resources, having severe scores of academic stress, and evening chronotype were associated with an increased probability to suffer a current depressive episode. Collectively, these results show that chronotype and PAS are factors associated with depression in MS, and when combined promote this association. Our results might aid in early identification of MS susceptible to depression. Future research could focus on the implementation of simple, low cost preventive strategies, such as chronotype-oriented academic schedules.

Circadian preferences and sleep in 15- to 20-year old Finnish students

Purpose

Despite progress in research concerning adolescent and young adult sleep and circadian preferences, several aspects have remained unexamined. This study explored gender and diurnal rhythms in relation to several sleep-related factors: sleep duration, bedtime, wake-up time, tiredness, sleepiness, and optimal subjective sleep duration

Methods

Circadian preferences and sleep were investigated in 555 (Females N=247) Finnish students aged 15–20. The self-report measures included a shortened version of the Horne-Östberg Morningness-Eveningness Scale, the Epworth Sleepiness Scale as well as items probing feelings of tiredness, optimal subjective sleep durations, and bedtime and wake-up time on the most recent day and a typical weekend. Data were collected from Tuesday to Thursday during an ordinary school week.

Results and conclusion

The most frequent chronotype was the intermediate type (54%), and compared to previous studies, the prevalence of evening-oriented individuals was high (37%), whereas only 9% of the participants were classified as morning oriented. No gender-specific or chronotype-specific differences in sleep durations were observed, but girls/women and evening-orientated individuals reported suffering more from sleepiness, compared to boys/men and more morning-typed participants, respectively. About 20% of the total sample indicated that their subjective need for sleep was not satisfied during the weekdays nor the weekend, indicating chronic sleep deprivation. Among girls/women and evening-oriented individuals, the subjective sleep need was greater for weekday nights.

Perceived morningness-eveningness predicts academic adjustment and substance use across university, but social jetlag is not to blame

Past research has consistently found that evening-types typically report poorer academic adjustment and higher levels of substance use compared to morning-types. An important development within the morningness-eveningness and psychosocial adjustment literature has been the hypothesis that social jetlag (i.e. the asynchrony between an individual's "biological" and "social" clocks) is one factor that may explain why evening-types are at a greater risk for negative psychosocial adjustment. Yet, only a handful of studies have assessed social jetlag. Furthermore, the few studies that have assessed social jetlag have done so only with concurrent data, and thus have not been able to determine the direction of effects among morningness-eveningness, social jetlag and psychosocial adjustment. To address this important gap in the literature, the present 3-year longitudinal study employed the use of a cross-lagged auto-regressive model to specifically examine the predictive role of perceived morningness-eveningness and social jetlag on two important indices of psychosocial adjustment among university students: academic adjustment and substance use. We also assessed whether there would be an indirect effect between perceived morningness-eveningness and psychosocial adjustment through social jetlag. Participants were 942 (71.5% female; M = 19 years, SD = 0.90) undergraduates at a mid-sized university in Southern Ontario, Canada, who completed a survey at three assessments, each one year apart, beginning in first-year university. Measures were demographics (age, gender and parental education), sleep problems, perceived morningness-eveningness, social jetlag, academic adjustment and substance use. As hypothesized, results of path analyses indicated that a greater perceived eveningness preference significantly predicted higher social jetlag, poorer academic adjustment and higher substance use over time. In contrast, we found no support for social jetlag as a predictor of academic adjustment and substance use, indicating that social jetlag did not explain the link between perceived morningness-eveningness and negative psychosocial adjustment. An important finding was the significant predictive effect of higher substance use on social jetlag over time. Results of the present study highlight the importance of employing a longitudinal framework within which to specifically determine the direction of effects among the study variables in order to validate proposed theoretical models that aim to guide our understanding of how perceived morningness-eveningness, social jetlag, academic adjustment and substance use relate to each other.

Validation of the Italian Version of the Morningness-Eveningness Questionnaire for Adolescents by A. Lancry and Th. Arbault

Background

This study aimed to validate the Italian version of the Morningness-Eveningness questionnaire for adolescents by Lancry and Arbault.

Material/Methods

The Morningness-Eveningness Questionnaire by Lancry and Arbault was translated from French into Italian by using forward-backward translation. Students aged 11–15 years old were enrolled from two schools in Milan (Italia). Validation of the questionnaire was performed in subsequent phases. A pre-test was given to 66 students aged 11–15 years (males 57.4%, females 42.6%) from a convenience sample. Syntactic aspects of the pre-test were improved, and the questionnaire in a revised version was re-administered to 292 students of same age (males 43.8%, females 54.1%) from a convenience sample.

Results

Factor analysis was performed on pre-test data, using the principal component method accounting for Morningness-Eveningness. Problematic items possibly uncorrelated with the extracted factor were identified, and reliability produced a Cronbach’s Alpha close to 0.7. In the test phase factor analysis was performed using the principal component method. Based on reliability analyses, we excluded a number of items because of their low performance, giving rise to a Cronbach’s Alpha of 0.819. Pearson product-moment external correlations between Morningness-Eveningness disposition and temperament, behavioral, and cognitive aspects were evaluated.

Conclusions

A factor analysis, Cronbach’s alpha and concurrent validity coefficients with disposition, behavior, and cognition, were performed, suggesting potential reliability and validity. The questionnaire is a useful and relevant tool for measuring Morningness-Eveningness disposition in adolescents, which has seldom been investigated with adequate psychometric instruments.