Circadian typology: a comprehensive review

A twin-study of genetic contributions to morningness-eveningness and depression

Circadian rhythms are associated with the preference for sleep-wake timing, also known as morningness-eveningness (ME). Both circadian rhythms and ME are influenced by genetic factors. Studies show an association between eveningness and depression. This study investigates the heritability of ME and whether ME and depression share common genetic influences. Study participants (n = 1237) were from the Vietnam Era Twin Study of Aging, a longitudinal study of aging with a baseline in midlife. Participants received the Morningness-Eveningness Questionnaire (MEQ) and the Center for Epidemiologic Studies Depression (CES-D) Scale as part of an extensive neurocognitive and psychosocial assessment. MEQ correlations between members of twin pairs were 0.41 (95% CI 0.31-0.49) for monozygotic (MZ) twins and 0.28 for dizygotic (DZ) twins (95% CI 0.19-0.41). CES-D correlations were 0.38 (95% CI 0.28-0.46) for MZ twins and 0.24 (95% CI 0.14-0.36) for DZ twins. Greater eveningness (i.e. lower MEQ scores) was significantly related to more depression symptoms (phenotypic correlation = -0.15 (95% CI -0.21 to -0.09). In the best fitting model, the heritability estimates are 0.42 for the MEQ and 0.37 for the CES-D. A significant genetic correlation of -0.21 indicated that ME and depression share a significant amount of their underlying genetic variance. The genetic covariance between ME and depression accounted for 59.1% of the phenotypic correlation. Of the CES-D sub-scales, Depressed Mood and Interpersonal Difficulties were significantly heritable, while only Well-Being had a significant genetic correlation with ME. ME and depression are both heritable (ME 0.42, depression 0.37) and share common genetic factors, suggesting an overlap in etiology and the relevance of circadian rhythms to depression. Further study of this relationship may help elucidate etiological factors in depression and targets for treatment.

Distribution and heritability of diurnal preference (chronotype) in a rural Brazilian family-based cohort, the Baependi study

Diurnal preference (chronotype) is a useful instrument for studying circadian biology in humans. It harbours trait-like dimensions relating to circadian period and sleep homeostasis, but also has ontogenetic components (morningness increases with age). We used the Morningness-Eveningness questionnaire (MEQ) in the Baependi study, a family-based cohort study based in a small town in Minas Gerais, Brazil. The population is highly admixed and has a cohesive and conservative lifestyle. 825 individuals (497 female) aged 18–89 years (average ± SD = 46.4 ± 16.3) and belonging to 112 different families participated in this study. The average MEQ score was 63.5 ± 11.2 with a significant (P < 0.0001) linear increase with age. Morningness was significantly (P < 0.0001) higher in the rural (70.2 ± 9.8) than in the municipal zone (62.6 ± 11.1), and was also significantly (P = 0.025) higher in male (64.6 ± 10.9) than in female (62.8 ± 11.2) participants. Thus, in spite of universal access to electricity, the Baependi population was strongly shifted towards morningness, particularly in the rural zone. Heritability of MEQ score was 0.48 when adjusted for sex and age, or 0.38 when adjusted for sex, age, and residential zone. The reported MEQ score heritability is more akin to those of previous twin studies than previous family studies.

Seasonality and its distinct clinical correlates in bipolar II disorder

Seasonality is one of the key features in subjects with mood disorders and is involved in the multi-faceted nature of the clinical course. However, few studies have explored the clinical implications of seasonality in bipolar disorders. We examined the differential effects of seasonality on clinical variables between bipolar I and II disorder (BD I and II). Seasonality was assessed using the Seasonal Pattern Assessment Questionnaire (SPAQ) in 204 subjects with BD I and 308 with BD II. Following the comparisons between BD I and II groups, clinical characteristics related to seasonality were explored. Next, to predict the presence of seasonality, a logistic regression model was applied. The global seasonality score on the SPAQ was significantly higher in the BD II group than in the BD I group. In the BD I group, seasonality was associated with suicide attempt history. In the BD II group, on the other hand, seasonality was associated with female gender, depressive predominance, and premenstrual dysphoric disorder (PMDD). In the regression models, the presence of PMDD and female gender was significantly associated with seasonality in the BD II group. Our findings suggest that high seasonality tendency, a vulnerability maker for cyclic worsening, may contribute to a differential pattern of clinical characteristics in BD II.

Theory of Inpatient Circadian Care (TICC): A Proposal for a Middle-Range Theory

The circadian system controls the daily rhythms of a variety of physiological processes. Most organisms show physiological, metabolic and behavioral rhythms that are coupled to environmental signals. In humans, the main synchronizer is the light/dark cycle, although non-photic cues such as food availability, noise, and work schedules are also involved. In a continuously operating hospital, the lack of rhythmicity in these elements can alter the patient’s biological rhythms and resilience. This paper presents a Theory of Inpatient Circadian Care (TICC) grounded in circadian principles. We conducted a literature search on biological rhythms, chronobiology, nursing care, and middle-range theories in the databases PubMed, SciELO Public Health, and Google Scholar. The search was performed considering a period of 6 decades from 1950 to 2013. Information was analyzed to look for links between chronobiology concepts and characteristics of inpatient care. TICC aims to integrate multidisciplinary knowledge of biomedical sciences and apply it to clinical practice in a formal way. The conceptual points of this theory are supported by abundant literature related to disease and altered biological rhythms. Our theory will be able to enrich current and future professional practice.

Dangerous driving in a Chinese sample: associations with morningness-eveningness preference and personality

Individual differences in morningness-eveningness preference may influence susceptibility and response to sleepiness. These differences could influence driving performance, but the influence of morningness-eveningness preference on driving behavior and accident risk has not been comprehensively studied. As morningness-eveningness preference is associated with personality characteristics, we also investigated how the interaction between morningness-eveningness preference and personality may be related to dangerous driving behaviors. Two hundred and ninety five drivers completed the reduced Morningness-Eveningness Questionnaire, the Dula Dangerous Driving Index, and personality scales for agreeableness, conscientiousness and neuroticism, and reported demographic information (gender, age, level of education, driving years and annual average driving mileage) and self-reported traffic violations (accidents, penalty points and fines). The results showed that more Risky Driving, Aggressive Driving, Negative Cognitive/Emotional Driving and Drunk Driving, as measured by the Dula Dangerous Driving Index, were all significantly correlated with more eveningness, corresponding to lower scores on the reduced Morningness-Eveningness Questionnaire. Moreover, eveningness was correlated with self-reported traffic accidents, penalty points and fines. Furthermore, a moderation effect was found: eveningness was more strongly associated with risky driving and negative emotional driving in those who scored high for trait agreeableness.

Age and gender variations of sleep in subjects without sleep disorders

OBJECTIVE

Although sleep is a biomarker for general health and pathological conditions, its changes across age and gender are poorly understood.

METHODS

Subjective evaluation of sleep was assessed by questionnaires in 5,064 subjects, and 2,966 were considered without sleep disorders. Objective evaluation was performed by polysomnography in 2,160 subjects, and 1,147 were considered without sleep disorders. Only subjects without sleep disorders were included (aged 40-80 years).

RESULTS

Aging was strongly associated with morning preference. Older subjects, especially women, complained less about sleepiness, and pathological sleepiness was significantly lower than in younger subjects. Self-reported sleep quality and daytime functioning improved with aging. Sleep latency increased with age in women, while sleep efficiency decreased with age in both genders. Deep slow-wave sleep decreased with age, but men were more affected. Spectral power densities within slow waves (< 5 Hz) and fast spindles (14-14.75 Hz) decreased, while theta-alpha (5-1 Hz) and beta (16.75-25 Hz) power in non-rapid eye movement sleep increased with aging. In REM sleep, aging was associated with a progressive decrease in delta (1.25-4.5 Hz) and increase in higher frequencies.

CONCLUSIONS

Our findings indicate that sleep complaints should not be viewed as part of normal aging but should prompt the identification of underlying causes.

Eveningness is Associated with Higher Risk-Taking, Independent of Sex and Personality

This study tested the hypotheses that eveningness is associated with higher risk-taking propensities across different domains of risk and that this association is not the result of sex differences or confounding covariation with particular personality traits. Study participants were 172 men and women between 20 and 40 years of age. Surveys assessed chronotype, domain-specific risk-taking and risk-perception, and Big Five personality dimensions. Eveningness was associated with greater general risk-taking in the specific domains of financial, ethical, and recreational decision making. Although risk-taking was associated with both risk perception and some personality dimensions, eveningness predicted risk-taking independent of these factors. Higher risk-taking propensities among evening types may be causally or functionally linked to their propensities for sensation- and novelty-seeking, impulsivity, and sexual promiscuity.

Sleep, circadian rhythms, and athletic performance

Sleep deprivation and time of day are both known to influence performance. A growing body of research has focused on how sleep and circadian rhythms impact athletic performance. This review provides a systematic overview of this research. We searched three different databases for articles on these issues and inspected relevant reference lists. In all, 113 articles met our inclusion criteria. The most robust result is that athletic performance seems to be best in the evening around the time when the core body temperature typically is at its peak. Sleep deprivation was negatively associated with performance whereas sleep extension seems to improve performance. The effects of desynchronization of circadian rhythms depend on the local time at which performance occurs. The review includes a discussion of differences regarding types of skills involved as well as methodological issues.

The personality profile of young adults with delayed sleep phase disorder

Delayed sleep phase disorder (DSPD) is a circadian rhythm sleep disorder characterized by a substantial delay in the major sleep period, resulting in difficulties falling asleep and awakening at a socially desirable time in the morning. This study is the first to investigate the NEO-Personality Inventory-Revised profile of young adults with DSPD. The study includes 40 patients diagnosed with DSPD (mean age = 20.7) and 21 healthy controls (mean age = 21.1). Results showed that young adults with DSPD scored higher on Neuroticism, lower on Extroversion, and much lower on Conscientiousness than the control group. Assessing the personality profile of young adults with DSPD before initiating treatment might provide useful clinical guidance regarding the individual needs for follow up during treatment.

The midpoint of sleep on working days: a measure for chronodisruption and its association to individuals' well-being

There is consistent evidence suggesting a relationship between individuals' sleep-wake rhythms and well-being. The indiscriminate demands from daily working routines, which do not respect this individual physiological rhythm, might be mediating this phenomenon. The aim of the present study was to evaluate the relationship between the characteristics of sleep routines during working days and psychological well-being. This was a cross-sectional study on 825 individuals from rural communities from southern Brazil. The study protocol included a questionnaire on demographic characteristics, working routines, health complaints, and habits; the Munich Chronotype Questionnaire for sleep-wake rhythm and; the WHO-Five well-being index. Since sex has been shown to affect sleep circadian rhythm and well-being, analysis was performed on men and women separately. In the proposed hierarchical regression models, different factors contributed to well-being according to sex. Among men, sleep-wake and work-related variables did not predict well-being scores. Among women, later midpoints of sleep on working days (B = -1.243, SE B = 0.315, β = -0.220), working more days per week (B = -1.507, SE B = 0.494, β = 0.150), having longer working journeys (B = -0.293, SE B = 0.105, β = -0.166), earlier working journey midpoints (B = 0.465, SE B = 0.222, β = 0.115), and being exposed to less sunlight (B = 0.140, SE B = 0.064, β = 0.103) predicted worse well-being. For the subgroup of women with days free from work, we have found a correlation between later midpoints of sleep during the week with worse well-being (Pearson's r = -0.159, p = 0.045) while the same relationship was not significantly observed with the midpoint of sleep on non-working days (Pearson's r = -0.153, p = 0.054). Considering WHO-Five as categorical, based on proposed clinical cut-offs, among women working 7-d/week, those with worst well-being (WHO-Five < 13) had the latest midpoint of sleep (F = 4.514, p = 0.012). Thus, the midpoint of sleep on working days represents the interaction between individuals' sleep-wake behavior and working routines. It plays an important role as a stress factor and may be a useful alternative variable related to chronodisruption.

Women would like their partners to be more synchronized with them in their sleep-wake rhythm

Men sleep shorter and go to bed and get up later than women, thus they are later chronotypes. This difference between the sexes is most pronounced between puberty and menopause indicating the possibility that morningness is subject to sexual dimorphism related to reproductive aspects. The objective of the study was to compare the sleep-wake behavior of women with their actual partners and with their preferred partners. As a hypothesis, we expect some assortment in mating concerning chronotype (with the actual partner), but we also expect a higher synchronization with a preferred ideal partner. 167 women were analyzed in this study (mean age: 23.0 ± 2.57 (SD) years). Mated women were earlier chronotypes than their partners (t = -2.051, p = .042, d = .34) but the difference was small (11:02 min ± 1:04 min). The results of the present study showed women preferring a partner synchronized to their own sleep-wake-rhythm more than their actual partners were. The above result was true either for single facets of the sleep-wake rhythm (e.g. bed time, sleep onset) or for midpoint of sleep on free days - an indicator of actual chronotype: women's and their partners' correlation of midpoint of sleep was lower (r = .513) than women's and their ideal partners' correlation (r = .855). Amongst various sleep-wake measures, women particularly preferred a partner going to bed at the same time. Assortative mating according to sleep-wake rhythm exists, but women for long-term pair-bonds would like their partners far more synchronized.

Do different circadian typology measures modulate their relationship with personality? A test using the Alternative Five Factor Model

The relationship between personality and circadian typology shows some inconsistent results and it has been hypothesized that the model used to measure personality might have a moderating effect on this relationship. However, it has never been explored if this inconsistency was dependent on the questionnaire used to measure differences in circadian rhythms as well. We explored this issue in a sample of 564 university students (32% men; 19-40 years) using the Zuckerman-Kuhlman Personality Questionnaire, which is based on an evolutionary-biological approach, in combination with the Composite Scale of Morningness (CSM) and the reduced Morningness-Eveningness Questionnaire (rMEQ). Both questionnaires detected differences between circadian typologies in Sociability (highest in evening types; ET) and Impulsive Sensation-Seeking scales (highest in ET), while the CSM also detected differences in Activity (lowest in ET) and Aggression-Hostility (highest in ET). Further, both questionnaires detected differences between circadian typologies in the subscales General Activity (morning types [MT] higher than ET), Impulsivity (ET highest) and Sensation-Seeking (highest in ET). Differences between circadian typologies/groups in the subscales Parties (highest in ET) and Isolation Intolerance (lowest in MT) were only detected by the rMEQ. The CSM clearly separated evening types from neither and morning types while the rMEQ showed that neither types are not intermediate but closer to evening types in General Activity and Isolation Intolerance, and closer to morning types in Impulsive Sensation-Seeking, Parties, Impulsivity and Sensation Seeking. The obtained results indicate that the relationship between circadian typology and personality may be dependent on the instrument used to assess circadian typology. This fact may help to explain some of the conflicting data available on the relationship between these two concepts.

Circadian preference and trait impulsivity, sensation-seeking and response inhibition in healthy young adults

Circadian preference has been considered related with impulsivity. The purpose of the present study was to evaluate the relationship between circadian typology and impulsivity measured by the Barratt Impulsivity Scale (BIS), sensation-seeking measured by the Sensation Seeking Scale - Form V (SSS-V) and response inhibition elicited by the GO/NO-GO paradigm. A total of 503 Korean healthy college students (288 males and 215 females) completed the Composite Scale of Morningness (CSM) for circadian typology and the BIS and SSS-V for impulsivity and risk taking, respectively. A subset of 142 subjects additionally performed the computerized GO/NO-GO task for motor response inhibition. A significant association was found between the circadian typology of the CSM and impulsivity of the BIS and disinhibition of SSS-V. In addition, there was a difference in trend level between the circadian typology and response inhibition elicited by the GO/NO-GO test. Regarding circadian preference, evening types were significantly associated with higher impulsivity on the BIS, disinhibition on the SSS-V and lower rate of successful inhibition on the GO/NO-GO task compared to morning types. The present results showed significant relationships between circadian preference and impulsivity and sensation-seeking personality traits. In particular, our findings suggest that high impulsivity, disinhibition and impaired response inhibition are more related to evening types. Circadian preference might be associated with psychiatric problems interacting with some aspects of personality traits such as inhibitory control.

Influence of shift work on early reproductive outcomes: a systematic review and meta-analysis

OBJECTIVE

To determine whether an association exists between shift work and early reproductive outcomes.

DATA SOURCES

MEDLINE, Embase, and Web of Science were searched. Additional sources included Google Scholar, the Cochrane Library, online publications of national colleges, the ClinicalTrials.gov, and references of retrieved papers.

METHODS OF STUDY SELECTION

Included studies compared female shift workers (work outside 8:00 AM to 6:00 PM) with nonshift workers with menstrual disruption (cycles less than 25 days or greater than 31 days), infertility (time-to-pregnancy exceeding 12 months), or early spontaneous pregnancy loss (less than 25 weeks).

TABULATION, INTEGRATION, AND RESULTS

Two reviewers extracted adjusted and raw data. Random effect models were used to pool data weighting for the inverse of variance. Assessments of heterogeneity, bias, and subgroup analyses were performed. Sixteen independent cohorts from 15 studies (123,403 women) were subject to analysis. Shift workers had increased rates of menstrual disruption (16.05% [2,207/13,749] compared with 13.05% [7,561/57,932] [n=71.681, odds ratio {OR} 1.22, 95% confidence interval {CI} 1.15-1.29, I 0%]) and infertility (11.3% [529/4,668] compared with 9.9% [2,354/23,811] [OR 1.80, 95% CI 1.01-3.20, I 94%]) but not early spontaneous pregnancy loss (11.84% [939/7,931] compared with 12.11% [1,898/15,673] [n=23,604, OR 0.96, 95% CI 0.88-1.05, I 0%]). Night shifts were associated with increased early spontaneous pregnancy loss (n=13,018, OR 1.29, 95% CI 1.11-1.50, I 0%). Confounder adjustment led to persistent relationships between shift work and menstrual disruption (adjusted OR 1.15, 95% CI 1.01-1.31, I 70%) but not infertility (adjusted OR 1.11 95% CI 0.86-1.44, I 61%). The association between night shifts and early spontaneous pregnancy loss remained (adjusted OR 1.41 95% CI 1.22-1.63, I 0%).

CONCLUSION

This review provides evidence for an association between performing shift work and early reproductive outcomes, consistent with later pregnancy findings. However, there is currently insufficient evidence for clinicians to advise restricting shift work in women of reproductive age.

The reliability and validity of the Japanese version of the Children's ChronoType Questionnaire (CCTQ) in preschool children

We aimed to examine the reliability and validity of the Japanese version of the Children's ChronoType Questionnaire (CCTQ) in preschool children. The CCTQ consists of 16 items on sleep-wake parameters for scheduled and free days, a 10-item of the Morningness/Eveningness Scale (CCTQ-M/E), and a single item on chronotype. Out of 502 children aged 3-6 years living in Okayama Prefecture, we evaluated 346 (188 boys and 158 girls) between May and June 2012. Their parents filled out the questionnaires two times at an interval of two weeks. Cronbach's α of the CCTQ-M/E was 0.77. For test-retest reliability, Pearson's correlation coefficient of the CCTQ-M/E between the two observations was 0.898 (p<0.001). Kruskal-Wallis test with post-hoc tests was used to compare sleep-wake parameters measured with the CCTQ among the three groups of children, morning (M)-type, neither (N)-type and evening (E)-type, who were classified according to the CCTQ-M/E score. Sleep-wake parameters in timing were significantly different among the children with M-type, N-type and E-type (p<0.001). Post-hoc pairwise comparisons revealed that sleep-wake parameters in timing were significantly delayed from the M-type to the N-type children (p<0.001), from the M-type to the E-type children (p<0.001), and from the N-type to the E-type children (p<0.001), except that wake-up time and get-up time were not significantly different between the children with N-type and E-type on scheduled days when their start time was regularly fixed. Out of these 346 children, we evaluated 72 (35 boys and 37 girls) to see the correlations between subjectively and objectively measured sleep-wake parameters from June to October 2012. Spearman's correlation coefficients between sleep-wake parameters measured with the CCTQ and an actigraph were 0.512-0.836 on scheduled days (p<0.001) and 0.380-0.786 on free days (p<0.001). Based on these findings we conclude that the Japanese version of the CCTQ is a reliable and valid measure for assessing chronotypes in preschool children.

Chronotype, gender, and time for sex

The study aimed at testing chronotype and gender differences in the time of day when humans feel the greatest need for sex and the time of day they actually undertake sexual activity. A Polish sample of 565 participants aged between 18 and 57 was tested. In females, regardless of chronotype, the greatest need for sex occurred between 18:00 and 24:00, but a secondary peak appeared only in morning types at 6:00-9:00. In males, the greatest need for sex occurred either in the morning or evening hours: in evening types at 9:00-12:00 and 18:00-3:00; in neither types at 6:00-9:00 and 18:00-24:00; in morning types at 6:00-12:00 and 18:00-24:00. Considering time of day when subjects were undertaking sexual activity most frequently, this appeared between 18:00 and 24:00 for all the participants, and prolonged until 3:00 at night in evening type males. Morningness preference was more strongly related to the timing of need for sex than to the timing of actual sexual activity (r = -0.275 vs. r = -0.174), while the timing of desire and the timing of sexual activity were positively, but moderately related (r = 0.320).

Effects of chronotype and time of day on the vigilance decrement during simulated driving

The current study tested for the first time the effect of individual differences in circadian rhythmicity (chronotype) on both driving performance and its evolution along time on task. Morning-type and evening-type female participants were tested in morning (8 am) and evening (8 pm) sessions, in which we controlled for prior sleep duration and prior wake. Measures of body temperature, subjective activation and affect, reaction times (RT) in the Psychomotor Vigilance Task (PVT), behavioral performance (error position) and EEG alpha power during simulated driving were collected. The main result showed strong linear increments of mean and standard deviation of error position along time on task (vigilance decrement) when evening-type participants drove at their non-optimal time of day, that is, during the morning session. In contrast, driving performance in the morning-type group remained stable over time on task and was not affected by time of day. This finding can be due to differences in personality traits (e.g., conscientiousness, sensation seeking) and task appraisal associated to extreme chronotypes. The consideration of chronotype in vigilance and driving tasks can enhance safety and human performance by promoting work schedules and countermeasures to prevent failures in the accomplishment of tasks under non-optimal circadian conditions.

Validity of the Japanese version of the Munich ChronoType Questionnaire

To assess circadian preference with a score, the Morningness-Eveningness Questionnaire (MEQ) has been used for more than 3 decades now. More recently, the Munich ChronoType Questionnaire (MCTQ) was developed: it asks for sleep-wake behavior on work and free days and uses the midpoint of sleep on free days (MSF), corrected for sleep debt accumulated during the work week as an indicator of chronotype (MSFsc). In this study, we developed a Japanese version of the MCTQ by using a translation/back-translation approach including an examination of its semantic validity. In a subsequent questionnaire survey, 450 adult men and women completed the Japanese versions of the MCTQ and MEQ. Results showed that MEQ scores were significantly negatively correlated with mid-sleep parameters assessed by the MCTQ, on both, work and free days, as well as with the chronotype measure MSFsc (r = -0.580 to -0.652, all p < 0.001). As in the original German version, the strongest correlation was observed between MEQ score and MSF. A physiological validation study using dim light melatonin onset as a circadian phase marker (N = 37) showed a high correlation between chronotype as assessed with the MSFsc (r = 0.542, p < 0.001), and less so for MEQ score (r = -0.402, p = 0.055). These results demonstrate the validity of the Japanese MCTQ and provide further support of the adequacy of the MCTQ as a chronotype measure.

Beyond physiological hypoarousal: the role of life stress and callous-unemotional traits in incarcerated adolescent males

The development of antisocial behavior in youth has been examined with neurobiological theories that suggest that adolescents who are less responsive to their environments are less likely to develop empathy in the absence of extant physiological arousal. However, little attention is paid to these individuals' social context. Individuals with adverse early experiences can also exhibit attenuated physiological arousal. The current investigation examines whether psychopathic symptoms or life stress exposure is associated with cortisol and its diurnal rhythm within 50 incarcerated adolescent boys (14-18years old). Ten saliva cortisol samples were collected 1-2weeks after admission to a maximum-security juvenile facility. Hierarchical Linear Modeling distinguished waking cortisol levels, the awakening response (CAR) and the diurnal rhythm. Multiple interviews and self-report measures of CU traits and stressor exposure were collected. Boys with higher levels of CU traits or greater life stress exposure had flat diurnal rhythms and a steeper awakening response in analyses with lifetime stress exposure specifically. Nonetheless, boys who were elevated on both CU traits and prior stress exposure had steeper diurnal rhythms. These results extend neurobiological theories of cortisol and illustrate that boys with the combination of severe stress with CU traits have a unique physiological profile.

A survey of college-bound high school graduates regarding circadian preference, caffeine use, and academic performance

BACKGROUND

This study examines the relationships between circadian preference and caffeine use with academic performance and hours spent studying for recent high school graduates entering their first year of college.

METHOD

Entering first-year college students enrolled at 90 baccalaureate-level institutions across the USA were invited to complete the Beginning College Survey of Student Engagement (BCSSE) and the Composite Scale of Morningness (CSM) as well as answer questions regarding caffeine consumption. Surveys were administered on each campus during the summer months of 2013. Only those that graduated from a US high school in the spring of 2013 were included in this study. The final sample for this study included 25,200 students that completed the BCSSE, CSM, and questions regarding caffeine consumption.

RESULTS

Evening types (E-types) were significantly less likely to report earning A/A-'s in high school and less likely to study 16 or more hours per week compared to intermediate or morning types (M-types) (p < 0.05). Overall, entering first-year students reported an average of 1.1 servings of caffeine per day, with 39 % reporting no caffeine consumption. M-types were more likely to consume no caffeine (54 %) compared to E-types that also indicated no daily caffeine (31 %) (p < 0.05). However, E-types were approximately 2.5 times more likely to consume three or more daily servings of caffeine (18 %) compared to M-types that consume the same amount (7 %) (p < 0.05). M-types that consumed no caffeine reported the highest grades with nearly 64 % reporting they earned mostly A's or A-'s in high school. However, the apparent advantage that morning types had over evening types regarding high school grades was completely ameliorated once three or more servings of caffeine were consumed per day.

CONCLUSIONS

This study provides additional information to educators and health professionals to create programs and provide resource to help adolescents better understand the impact of their sleep behaviors and use of caffeine on their academic performance.

Study of a Functional Polymorphism in the PER3 Gene and Diurnal Preference in a Colombian Sample

Polymorphisms in human clock genes have been evaluated as potential factors influencing circadian phenotypes in several populations. There are conflicting results for the association of a VNTR in the PER3 gene and diurnal preference in different studies. The objective of this study was to investigate the association between diurnal preference and daytime somnolence with the PER3 VNTR polymorphism (rs57875989) in healthy subjects from Colombia, a Latin American population.A total of 294 undergraduate university students from Bogotá, Colombia participated in this study. Two validated self-report questionnaires, the Composite Scale of Morningness (CSM) and the Epworth Sleep Scale (ESS) were used to assess diurnal preference and daytime somnolence, respectively. Individuals were genotyped for the PER3 VNTR using conventional PCR. Statistical comparisons were carried out with PLINK and SNPStats programs.

The PER3 VNTR polymorphism was not associated with either diurnal preference or daytime somnolence in this population. No significant differences in mean scores for those scales were found between PER3 VNTR genotypes. In addition, there were no differences in allelic or genotypic frequencies between chronotype categories. This is consistent with several negative findings in other populations, indicating that the proposed influence of this polymorphism in diurnal preference, and related endophenotypes of neuropsychiatric importance, needs further clarification. This is the first report of molecular genetics of human circadian phenotypes in a Spanish-speaking population.

Mind wandering, sleep quality, affect and chronotype: an exploratory study

Poor sleep quality impairs cognition, including executive functions and concentration, but there has been little direct research on the relationships between sleep quality and mind wandering or daydreaming. Evening chronotype is associated with poor sleep quality, more mind wandering and more daydreaming; negative affect is also a mutual correlate. This exploratory study investigated how mind wandering and daydreaming are related to different aspects of sleep quality, and whether sleep quality influences the relationships between mind wandering/daydreaming and negative affect, and mind wandering/daydreaming and chronotype. Three surveys (Ns = 213; 190; 270) were completed with Chinese adults aged 18-50, including measures of sleep quality, daytime sleepiness, mind wandering, daydreaming, chronotype and affect (positive and negative). Higher frequencies of mind wandering and daydreaming were associated with poorer sleep quality, in particular with poor subjective sleep quality and increased sleep latency, night-time disturbance, daytime dysfunction and daytime sleepiness. Poor sleep quality was found to partially mediate the relationships between daydreaming and negative affect, and mind wandering and negative affect. Additionally, low positive affect and poor sleep quality, in conjunction, fully mediated the relationships between chronotype and mind wandering, and chronotype and daydreaming. The relationships between mind wandering/daydreaming and positive affect were also moderated by chronotype, being weaker in those with a morning preference. Finally, while daytime sleepiness was positively correlated with daydream frequency, it was negatively correlated with a measure of problem-solving daydreams, indicating that more refined distinctions between different forms of daydreaming or mind wandering are warranted. Overall, the evidence is suggestive of a bi-directional relationship between poor sleep quality and mind wandering/daydreaming, which may be important in attempts to deal with sleep problems and improve sleep quality. These findings and further research on this topic may also have implications for definitions and theories of mind wandering and daydreaming.

Risk behaviors and negative health outcomes for adolescents with late bedtimes

Late bedtimes in adolescence may be a serious risk factor for later poor health and functional outcomes. The current study sought to extend existing cross sectional data by examining whether late bedtimes in adolescence predicts poor outcomes in young adulthood. Data from wave 2 (1996) and wave 3 (2001-2002) of the nationally representative sample of US youth (National Longitudinal Study of Adolescent Health) was used to examine the longitudinal relationship between late bedtime, and several risk behaviors and negative health outcomes following 3,843 adolescents into young adulthood. At wave 2 the mean age was 16 with 52.1% female. At wave 3 the mean age was 21.8. In cross sectional analyses, late bedtime was associated with 1.5 to over 3 times greater odds of involvement in risk behaviors and negative health outcomes, including emotional distress, suicidality, criminal and violent activity, and use of cigarettes, alcohol and illicit drugs. In longitudinal analyses, late bedtime assessed at wave 2 predicted a number of serious health outcomes at wave 3, with late bedtime in adolescence associated with around 1.5 greater odds of involvement in health jeopardizing behaviors such as criminal activity, alcohol abuse, cigarette use, illicit drug use and emotional distress in young adulthood. There was also a dose effect, such that the later the bedtime in adolescence, the greater the risk of involvement in risk behaviors in young adulthood. This research suggests that late bedtime in adolescence predicts multiple serious risk behaviors and health outcomes in young adulthood.

A human sleep homeostasis phenotype in mice expressing a primate-specific PER3 variable-number tandem-repeat coding-region polymorphism

In humans, a primate-specific variable-number tandem-repeat (VNTR) polymorphism (4 or 5 repeats 54 nt in length) in the circadian gene PER3 is associated with differences in sleep timing and homeostatic responses to sleep loss. We investigated the effects of this polymorphism on circadian rhythmicity and sleep homeostasis by introducing the polymorphism into mice and assessing circadian and sleep parameters at baseline and during and after 12 h of sleep deprivation (SD). Microarray analysis was used to measure hypothalamic and cortical gene expression. Circadian behavior and sleep were normal at baseline. The response to SD of 2 electrophysiological markers of sleep homeostasis, electroencephalography (EEG) θ power during wakefulness and δ power during sleep, were greater in the Per3^5/5 mice. During recovery, the Per3^5/5 mice fully compensated for the SD-induced deficit in δ power, but the Per3^4/4 and wild-type mice did not. Sleep homeostasis-related transcripts (e.g., Homer1, Ptgs2, and Kcna2) were differentially expressed between the humanized mice, but circadian clock genes were not. These data are in accordance with the hypothesis derived from human data that the PER3 VNTR polymorphism modifies the sleep homeostatic response without significantly influencing circadian parameters.—Hasan, S., van der Veen, D. R., Winsky-Sommerer, R., Hogben, A., Laing, E. E., Koentgen, F., Dijk, D.-J., Archer, S. N. A human sleep homeostasis phenotype in mice expressing a primate-specific PER3 variable-number tandem-repeat coding-region polymorphism.

The vigilance decrement in executive function is attenuated when individual chronotypes perform at their optimal time of day

Time of day modulates our cognitive functions, especially those related to executive control, such as the ability to inhibit inappropriate responses. However, the impact of individual differences in time of day preferences (i.e. morning vs. evening chronotype) had not been considered by most studies. It was also unclear whether the vigilance decrement (impaired performance with time on task) depends on both time of day and chronotype. In this study, morning-type and evening-type participants performed a task measuring vigilance and response inhibition (the Sustained Attention to Response Task, SART) in morning and evening sessions. The results showed that the vigilance decrement in inhibitory performance was accentuated at non-optimal as compared to optimal times of day. In the morning-type group, inhibition performance decreased linearly with time on task only in the evening session, whereas in the morning session it remained more accurate and stable over time. In contrast, inhibition performance in the evening-type group showed a linear vigilance decrement in the morning session, whereas in the evening session the vigilance decrement was attenuated, following a quadratic trend. Our findings imply that the negative effects of time on task in executive control can be prevented by scheduling cognitive tasks at the optimal time of day according to specific circadian profiles of individuals. Therefore, time of day and chronotype influences should be considered in research and clinical studies as well as real-word situations demanding executive control for response inhibition.

Impact of chronotype and time perspective on the processing of scripts

Little is known about the impact of temporal orientation (chronotype; time perspective) on cognitive performance. This study adopted a psychophysiological approach to explore how chronotype (morningness-eveningness) and time perspective (present; future) influence time succession as another aspect of psychological time that is entailed within script knowledge. In a temporal judgment task, participants decided which of the two presented sub-events (e.g., get new batteries-set right time on alarm clock) comes earlier (or later) within a given script (e.g., changing batteries in an alarm clock). Behavioral and pupillary data suggest a differential impact of chronotype and time perspective on script knowledge and cognitive performance. The impact of time perspective on the processing of temporal information entailed in script knowledge appears linked to match or mismatch conditions between a strong focus on future outcomes associated with future time perspective and the task of identifying either the later (future-oriented) or the earlier (past-oriented) sub-event. Concerning the chronotype, evening types process items in which chronological time succession is violated (i.e., reversely presented items) more accurately than morning types. Indexed by pupillary data, the impact of chronotype may relate to more general cognitive abilities. The psychophysiological data derived in this study suggests that evening types typically outperform morning types in various measures such working memory capacity and verbal intelligence simply because they invest more cognitive resources than morning types.