Gender differences in morningness–eveningness assessed by self-report questionnaires: A meta-analysis

The relationship between chronotype and depressive symptoms: A meta-analysis

BACKGROUND

Expanding our understanding of the factors that influence depression is crucial for prognosis and treatment. In light of increasing evidence of an association between disrupted circadian rhythms and affective symptoms, a meta-analysis was used to examine the relationship between an eveningness chronotype and depression.

METHODS

Electronic searches of the PsycINFO, Medline, Scopus, and Google Scholar databases were conducted in February 2016. Relevant reviews, related journals, and reference lists were manually searched. Statistical data were reported or transformed to a Fisher's z correlational coefficient for effect size analysis.

RESULTS

Data from 36 studies (n =15734) met the inclusion criteria and were analysed under a random effects model. Nearly all included studies utilised the Composite Scale of Morningness (CSM) or the Morningness-Eveningness Questionnaire (MEQ) as a measure of chronotype. Overall effect size from 58 effect sizes was small (z=-.20; 95% CI: -.18 to -.23). Effect sizes based on the CSM were significantly larger than those based on the MEQ. There was no evidence of publication bias.

LIMITATIONS

The number of studies comparing different mood disorders or the potential moderating effects of gender and age were too few to draw conclusions regarding their respective effect sizes. Future research should utilise longitudinal designs to draw causal inferences on the directionality of this relationship.

CONCLUSIONS

Findings from this meta-analysis indicate an eveningness orientation is somewhat associated with more severe mood symptoms. Chronobiological approaches may contribute to the prevention and treatment of depressive disorders.

Temperament and chronotype among academic athletes – perspective of the regulative theory of temperament

<b>Background</b><br /> The aim of the research was to evaluate the relationship between chronotype and temperamental traits and temperament structure specified in the Regulative Theory of Temperament among physical education students who are actively engaged in sport. The analyses were performed separately in groups of men, women, and individual and team sports representatives. <br /> <br /> <b>Participants and procedure </b><br /> The study included 157 participants (women n = 35, men n = 122; individual sports n = 88 and team sports n = 69). Measures used in the study were the Formal Characteristics of Behaviour – Temperament Inventory (FCB-TI) and the Morningness-Eveningness Questionnaire (MEQ). <br /> <br /> <b>Results </b><br /> Among women and men chronotype was positively correlated with Briskness (BR) and Endurance (EN). In women chronotype was negatively related to Emotional Reactivity (ER). Sensory Sensitivity (SS) was positively associated with chronotype in men. In the individual sport group chronotype was associated with four temperamental traits: BR, EN, ER (negatively) and SS. Activity (AC) significantly correlated with chronotype in the team sport group. Two out of three indicators of temperament structure – potential for stimulation processing (MPS) and structure harmony parameter (Zh1) – were related to chronotype in both genders. <br /> <br /> <b>Conclusions</b><br /> The results obtained in the present research indicate that temperament is significantly related to chronotype. Evening chronotype men and women might be overstimulated and morning types might be understimulated. These data might be useful for coaches and provide a guide for further individualization of the training process.

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

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

Spanish Adaptation of the Morningness-Eveningness-Stability-Scale improved (MESSi)

The aim of the present study was to conduct the preliminary adaptation of the Morningness-Eveningness-Stability-Scale improved (MESSi) to Spanish population, testing its factor structure and construct validity. Participants were 261 adults (65% women;M= 31.4,SD= 12.01) who filled out measures of Morningness-Eveningness (MESSi and CSM), sleep habits, personality traits, positive and negative affect, and subjective level of alertness during the day. Psychometric results supported a three factorial model with the factors Morning Affect, Eveningness and Distinctness (RMSEA = .072). The factors showed good internal consistence (α = 0.72–0.85). The pattern of correlations between MESSi and the other measures were in the expected direction (low to moderated size effects). Morning Affect was positively predicted by morning chronotype (R2= .64), Eveningness was negatively predicted by age and positively by evening chronotype (R2= .41), and Distinctness was negatively predicted by sex (women reported higher DI than men) and age (R2= .08). This study provides evidence for the factor structure of a new measure of Morningness-Eveningness based on a rigorous psychometric evaluation.

Relationship between chronotype and temperament/character among university students

Chronotype is largely classified as being morning or evening types according to preference for daily activity and the preferred bedtime. This study examined the relationship between chronotype and temperament/character dimensions among university students. A total of 2857 participants completed the 140-item Temperament and Character Inventory-Revised Short version (TCI-RS) from a 5-score scale as well as the 13-item composite scale for morningness-eveningness (CSM). In this study, we classified chronotype as "morning," "neither," or "evening" types according to CSM scores and compared the scores in terms of 4 temperament dimensions and 3 character dimensions. The evening type showed high values for novelty seeking and harm avoidance, whereas the morning type had high scores for persistence, self-directedness, and cooperativeness. A logistic regression analysis after controlling for age and gender showed that chronotype significantly associated with persistence and novelty seeking. The results of this study suggest that chronotype is different according to gender and age and in addition, chronotype closely correlates with temperament and character. Among these, eveningness was associated with high novelty seeking, whereas morningness was associated with high persistence. Further studies are required to investigate the relationship between chronotype and temperament/character dimensions in a wider age bracket.

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.

Eveningness associates with smoking and sleep problems among pregnant women

Sleep problems during pregnancy impair maternal health and increase the risk for adverse pregnancy outcome. The circadian preference toward eveningness has been associated with sleep problems in previous studies. Here, we studied whether evening-type women had more sleep problems during their pregnancy, as compared with other chronotypes, in a sample consisting of 1653 pregnant women from the Finnish CHILD-SLEEP Birth Cohort. Chronotype was assessed with a shortened version of the morningness-eveningness questionnaire. Pregnant evening-type women reported more sleep problems, including troubles of falling asleep (OR = 3.4, p < 0.0001), poor sleep quality (OR = 2.9, p < 0.01) and daily tiredness (OR = 3.2, p < 0.0001) than the morning-type women, even after controlling for sleep duration and sleep deprivation. They had higher scores on Epworth Sleepiness Scale (p < 0.05), Basic Nordic Sleep Questionnaire (p < 0.0001) and Global Seasonality Score (p < 0.01) and were also more often smokers, also during pregnancy (p < 0.001) and reported poorer general health (p < 0.001) than the morning-type women. They also reported having had more sleep problems during their childhood (OR = 1.5, p < 0.05) and adolescence (OR = 2.0, p < 0.001) than the morning-type women. Our results indicate that eveningness is associated with more sleep problems and unhealthy life habits during pregnancy.

Psychometric properties of Persian version of Composite Scale of Morningness

BACKGROUND

Morningness-eveningness preference is commonly measured by questionnaires such as the Composite Scale of Morningness (CSM). The purpose of this study is to assess the Persian translation of the CSM and explore its psychometric properties.

METHOD

Participants consisted of 288 students at the University of Bojnord, Iran. Of the participants selected, 47.6% were female, 52.4% were male, and all were aged between 18 and 24 (20.09±1.32). Participants were selected using the stratified random sampling method. The scale was translated into Persian using the parallel translation method. SPSS-22 and AMOS-22 were used for analyses.

RESULTS

Mean CSM scores were 31.43±6.32 in a range of 14-50. Internal reliability, as measured by Cronbach's α, was 0.790, which fits well with previous studies undertaken in many countries. The factor analysis revealed a two-factor structure based on parallel analysis: one factor was labeled as "morning affect" and the other as "self-assessment/activity planning." Also, the confirmatory factor analysis supported the two-factor model fit. Construct validity was also evaluated by the MEQ with the results showing that correlations were comparable to other studies (r=0.76). Results did not show any significant correlation between age (r=0.041; P=0.487) and the CSM scores. According to the results of the t-test, women and men were not significantly different in terms of the CSM scores (t=-0.264; P=0.792).

CONCLUSIONS

The Persian version of the CSM is freely available and can be adopted for behavioral research related to sleep and circadian function and also applied to other Persian-speaking populations.

Circadian preferences in young adults: Psychometric properties and factor structure of the Portuguese version of the Preferences Scale (PS-6)

Morningness is a trait-like variable which has been extensively studied within chronobiology. Despite the number of existing measures to assess morningness, there is a need for brief instruments that are psychometrically sound to be used in applied settings. Accordingly, the modified version of the Preferences Scale (PS-6) comprises six items and was reported to have adequate reliability and satisfactory validity indicators. In this article, the psychometric properties of the Portuguese version of the PS-6 are reported. A total of 700 students attending medical school were recruited, and this sample was randomly divided into two groups. In the first group (n = 352), we assessed the internal consistency calculations and conducted a principal component analysis of the posited structure. In the second group (n = 348), we conducted a confirmatory factor analysis (CFA) using structural equation modeling. Overall, the results indicated that the PS-6 has adequate reliability (α = .75) and is constituted by two components: (I) preferred cognitive activities timings and (II) preferred sleeping-eating timings, respectively. In conclusion, the Portuguese version of the PS seems suitable for use in research and applied settings such as shift work schedules management. However, the applicability of the PS-6 in other samples and further validity indicators should be both investigated. The use of actigraphy and biological measures should also be collected to enhance the robustness of the PS-6.

Cross-cultural validity of Morningness-Eveningness Stability Scale improved (MESSi) in Iran, Spain and Germany

Morningness-Eveningness Stability Scale improved (MESSi) is a newly constructed measure to assess circadian types and amplitude. In this study, we applied this measure to participants from three different countries: Germany, Spain and Iran. Confirmatory factorial analysis (CFA) of MESSi displayed mediocre fit in the three countries. Comparing increasingly stringent models using multigroup confirmatory factor analyses indicated at least partial measurement invariance (metric invariance) by country for Morning Affect and Distinctness subscales. Age was positively related to Morning Affect (MA), and negatively related to Eveningness (EV) and Distinctness (DI). Men reported higher MA than women, whereas women reported higher DI than men. Regarding country effect, Iranian participants reported highest MA compared to Spaniards and Germans, whereas Germans reported higher DI compared to Iranians and Spaniards. As a conclusion, our study corroborated the validity and reliability of MESSi across three different countries with different geographical and cultural characteristics.

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.

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

People differ in their sleep-wake behavior. This individual difference is conceptualized in different aspects, such as wake up times, bed times, times of peak performance, as well as in morning affect. A total of 14,987 visitors of an exhibition in the LWL State Museum of Natural History, Münster (Germany), did the survey on chronotype and gave their consent that these data can be used for a scientific study. Age groups were coded into 5-year bins. Mean age (mean ± SD) was 28.2 ± 17.5 years. There were 8075 females (54%) and 6912 males in the sample. The German version of the rMEQ (reduced Morningness-Eveningness-Questionnaire) was used for data collection. The data showed clear age effects. Younger children are more morning oriented and become rapidly evening oriented during puberty, while the more attenuated turn towards morningness occurs from the age of 20 years. Then between the ages 25 to 30 morningness-eveningness remained rather stable. Significant gender differences existed in the reproductive age, i.e., the age groups 20 to 50 (corresponding to the age 16–50 years). In other age groups, no gender differences could be detected. Seasonal effects were also found. Chronotype score was lowest during the summer months (and more evening oriented). Based on the single item analysis of the five questions of the rMEQ, we found age group differences in all items. Gender differences occurred in all items except item 1, which deals with the preferred wake-up time. Men always scored significantly lower (i.e. more evening oriented) than women except in item 2 (tiredness after awakening). Seasonal effects were only significant in item 3, which is related to preferred bed times. People showed a later bed time preference during summer. The classification of chronotypes according to the cut-off scores provided by Adan and Almirall (1991) and by using the 20/80 percentile provided identical cut-off scores (values of 11 and below for evening types and 18 and above for morning types).

Two in a bed: The influence of couple sleeping and chronotypes on relationship and sleep. An overview

Objective: To summarize research on couple sleeping with respect to gender-specific differences and chronotype. Methods: Systematic review of the literature. Results: Millions of adults around the world share their beds with a partner. This may be an expression of intimacy and attachment and tends to intensify romantic relationships. Yet, couple sleeping still has underestimated implications for the quality of the relationship, quality of sleep and for physical and psychological health which are not consistently positive. Implications for research and therapy are discussed. Conclusions: Despite the people involved perhaps not even being aware of their nocturnal interactions, it is important that sleeping together becomes a subject of discussion.

Abbreviations: REM: rapid eye movement; QOL: quality of life; OSA: obstructive sleep apnea; CPAP: continuous positive airway pressure

Morningness-eveningness and depressive symptoms: Test on the components level with CES-D in Polish students

BACKGROUND

The study aimed to elucidate previously observed associations between morningness-eveningness and depressive symptomatology in university students. Relations between components of depressive symptomatology and morningness-eveningness were analysed.

METHODS

Nine hundred and seventy-four university students completed Polish versions of the Centre for Epidemiological Studies - Depression scale (CES-D; Polish translation appended to this paper) and the Composite Scale of Morningness. Principal component analysis (PCA) was used to test the structure of depressive symptoms. Pearson and partial correlations (with age and sex controlled), along with regression analyses with morning affect (MA) and circadian preference as predictors, were used.

RESULTS

PCA revealed three components of depressive symptoms: depressed/somatic affect, positive affect, interpersonal relations. Greater MA was related to less depressive symptoms in three components. Morning circadian preference was related to less depressive symptoms in depressed/somatic and positive affects and unrelated to interpersonal relations. Both morningness-eveningness components exhibited stronger links with depressed/somatic and positive affects than with interpersonal relations. Three CES-D components exhibited stronger links with MA than with circadian preference. In regression analyses only MA was statistically significant for positive affect and better interpersonal relations, whereas more depressed/somatic affect was predicted by lower MA and morning circadian preference (relationship reversed compared to correlations).

LIMITATIONS

Self-report assessment.

CONCLUSIONS

There are three groups of depressive symptoms in Polish university students. Associations of MA with depressed/somatic and positive affects are primarily responsible for the observed links between morningness-eveningness and depressive symptoms in university students. People with evening circadian preference whose MA is not lowered have less depressed/somatic affect.

Extreme late chronotypes and social jetlag challenged by Antarctic conditions in a population of university students from Uruguay

In humans, a person’s chronotype depends on environmental cues and on individual characteristics, with late chronotypes prevailing in youth. Social jetlag (SJL), the misalignment between an individual׳s biological clock and social time, is higher in late chronotypes. Strong SJL is expected in Uruguayan university students with morning class schedules and very late entertainment activities. Sleep disorders have been reported in Antarctic inhabitants, that might be a response to the extreme environment or to the strictness of Antarctic life. We evaluated, for the first time in Uruguay, the chronotypes and SJL of 17 undergraduate students of the First Uruguayan Summer School on Antarctic Research, using Munich Chronotype Questionnaire (MCTQ) and sleep logs (SL) recorded during 3 phases: pre-Antarctic, Antarctic, and post-Antarctic. The midsleep point of free days corrected for sleep debt on work days (MSFsc,) was used as proxy of individuals’ chronotype, whose values (around 6 a.m.) are the latest ever reported. We found a SJL of around 2 h in average, which correlated positively with MSFsc, confirming that late chronotypes generate a higher sleep debt during weekdays. Midsleep point and sleep duration significantly decreased between pre-Antarctic and Antarctic phases, and sleep duration rebounded to significant higher values in the post-Antarctic phase. Waking time, but not sleep onset time, significantly varied among phases. This evidence suggests that sleep schedules more likely depended on the social agenda than on the environmental light–dark shifts. High motivation of students towards Antarctic activities likely induced a subjective perception of welfare non-dependent on sleep duration.

Ontogeny of morningness-eveningness across the adult human lifespan

Sleep timing of humans can be classified alongside a continuum from early to late sleepers, with some people (larks) having an early activity, early bed, and rise times and others (owls) with a more nocturnally orientated activity. Only a few studies reported that morningness-eveningness changes significantly during the adult lifespan based on community samples. Here, I applied a different methodological approach to seek for evidence for the age-related changes in morningness-eveningness preferences by using a meta-data from all available studies. The new aspect of this cross-sectional approach is that only a few studies themselves address the age-related changes of the adult lifespan development, but that many studies are available that provide exactly the data needed. The studies came from 27 countries and included 36,939 participants. Age was highly significantly correlated with scores on the Composite Scale of Morningness (r = 0.70). This relationship seems linear, because a linear regression explained nearly the same amount of variance compared to other models such as logarithmic, quadratic, or cubic models. The standard deviation of age correlated with the standard deviation of CSM scores (r = 0.55), suggesting when there is much variance in age in a study; in turn, there is much variance in morningness. This meta-analytical approach shows that morningness-eveningness changes across the adult lifespan and that older age is related to higher morningness.

Chronotypes in patients with nonseasonal depressive disorder: Distribution, stability and association with clinical variables

The individual's chronotype is regarded as rather stable trait with substantial heritability and normal distribution of the "morningness-eveningness" dimension in the general population. Eveningness has been related to the risk of developing affective, particularly depressive, disorders. However, age and other sociobiological factors may influence chronotypes. The present study investigated the distribution, stability, and clinical correlates of chronotype and morningness-eveningness in hospitalized patients with affective disorder. Chronotype was assessed with the morningness-eveningness questionnaire (MEQ) in 93 patients with nonseasonal depressive syndrome (85% major depression; 15% depressive adjustment disorder) after admission, and in 19 patients again before discharge. Distribution, stability and correlations of MEQ scores with clinical variables were calculated. Additionally, a literature analysis of chronotype distributions in samples of nondepressed persons and patients with nonseasonal depression was carried out. MEQ scores (mean 49 ± 11, range 23-75, higher scores indicate morningness) in 93 acutely depressed inpatients (age 41 ± 14 years, range 18-75 years; 63% women; hospitalization 48 ± 22 days; BDI-II 32 ± 11) were normally distributed (Shapiro-Wilk test; W = 0.993, p = 0.920) with 59.1% intermediate types, 19.4% evening types, and 21.5% morning types. MEQ change scores from admission to discharge were nonsignificant (-1.3 ± 5.0; paired t-test, t18 = -1.09; p = 0.29) despite significantly improved depression scores (-19.4 ± 7.6; paired t-test, t18 = 11.2, p < 0.001). Age (r = 0.24), and depression scores (r = -0.21) correlated significantly (p < 0.05) with MEQ scores; associations with sex and hospitalization duration were nonsignificant. The present study and literature findings revealed that the frequency of evening types is not clearly elevated in depression, but morning types are less frequent compared to healthy samples (p < 0.001). Morningness-eveningness scores were normally distributed and stable in depressive inpatients. In line with previous findings, but contrary to theoretical assumptions, evening types were not overrepresented in depressed patients. Additionally, relatively less morning types and more intermediate types were found in depressed patients. Future studies should focus on transitions from morning to intermediate types as a tentative risk or correlate of emerging depression.

Gender Difference in Timing of Nocturnal Rise of Subjective Sleepiness

Abstract. Experimental research of diurnal variations in body temperature and melatonin secretion consistently revealed an earlier entrained circadian phase in women than in men. Since it is well documented that daily fluctuations in self-reported level of sleepiness closely follow the circadian rhythms of melatonin and body temperature, one can predict that gender differences in phase characteristics of the 24-hour fluctuations of subjective sleepiness resemble the differences revealed by research of physiological and hormonal rhythms. Analysis of sleepiness self-scored by 46 male and 54 female participants of sleep deprivation experiments showed that female participants scored significantly higher their midnight sleepiness level. The model-based simulations of sleepiness curves confirmed the prediction of a relatively earlier phase of 24-hour oscillations of sleepiness in women. Such gender differences persisted after accounting for individual variation in habitual sleep times and morning-evening preference. In today’s environment, the earlier circadian phase in women can cause a larger delaying phase shift in response to midnight exposure to artificial light, but, on the other hand, the earlier rise of subjective sleepiness can make them less vulnerable to the delaying shifts.

Regional gray matter density is associated with morningness-eveningness: Evidence from voxel-based morphometry

Diurnal preference (morningness-eveningness) is known to be associated with several individual characteristics that are important in the fields of sociology, education, and psychiatry. Despite this importance, the anatomical correlates of individual differences in morningness-eveningness are unknown, and these were investigated in the present study. We used voxel-based morphometry and a questionnaire to determine individual morningness-eveningness and its association with brain structures in 432 healthy men and 344 healthy women (age, 20.7±1.8years). We demonstrated that morningness (less eveningness) was associated with (a) lower regional gray matter density (rGMD) in the precuneus and adjacent areas, (b) lower rGMD in the left posterior parietal cortex and adjacent areas, and (c) higher rGMD in the bilateral orbitofrontal cortex. Further, our exploratory analyses revealed that (d) higher rGMD in hypothalamic areas around the bilateral suprachiasmatic nuclei were associated with morningness. These findings demonstrate that variations in morningness-eveningness reflect the GM structures of focal regions across the cortex, and suggest a structural basis for individual morningness-eveningness and its association with a wide range of psychological variables distributed across different GM areas of the brain.

Circadian typology and the Alternative Five-Factor Model of personality

Two studies were carried out to explore the relationship between circadian typology and the Alternative Five-Factor Model of personality. In the first study, 379 participants (232 females) were administered the reduced version of the Morningness-Eveningness Questionnaire and the Zuckerman-Kuhlman Personality Questionnaire. Evening types reported higher impulsive sensation-seeking scores than morning and intermediate types, whereas morning types scored higher than evening types on activity factor. In the second study, the association between morningness and activity personality factor was verified through the objective-actigraphic monitoring of the rest-activity cycle. Actigraphy allowed us to operationalise both circadian typology, through the computing of midpoint of sleep (early values, expressed in hours and minutes, correspond to an advanced phase of the sleep/wake cycle), and activity factor by the means of motor activity recording. Fifty-one individuals (30 females) wore an actigraph on the nondominant wrist continuously for 1 week. A negative correlation was observed between midpoint of sleep and mean diurnal motor activity, demonstrating that an early phase of the sleep/wake cycle (i.e. morningness preference) was related to higher diurnal motor activity. Assessed both subjectively and objectively, the results of both studies highlight a significant relationship between morningness and activity personality factor.

Digital Sleep Logs Reveal Potential Impacts of Modern Temporal Structure on Class Performance in Different Chronotypes

Stability of sleep and circadian rhythms are important for healthy learning and memory. While experimental manipulations of lifestyle and learning outcomes present major obstacles, the ongoing increase in data sources allows retrospective data mining of people’s sleep timing variation. Here I use digital sleep-log data generated by 1109 students in a biology lab course at the University of Washington to test the hypothesis that higher variance in time asleep and later sleep-onset times negatively correlate with class performance, used here as a real-world proxy for learning and memory. I find that sleep duration variance and mean sleep-onset times both significantly correlate with class performance. These correlations are powerful on weeknights but undetectable on Friday and Saturday nights (“free nights”). These correlations also show sex differences, with women showing stronger (both larger and more powerful) negative correlations than men. Finally, although these data come with no demographic information beyond sex, the constructed demographic groups of “larks” and “owls” within the sexes reveal a significant decrease in performance of owls relative to larks in male students, whereas the correlation of performance with sleep-onset time for all male students was only a near-significant trend. This provides a proof of concept that deeper demographic mining of digital logs in the future may identify subgroups for which certain sleep phenotypes have greater predictive value for performance outcomes. The data analyzed are consistent with known patterns, including sleep-timing delays from weeknights to free nights and sleep-timing delays in men relative to women. These findings support the hypothesis that modern schedule impositions on sleep and circadian timing have consequences for real-world learning and memory. This study also highlights the low-cost, large-scale benefits of personal, daily, digital records as an augmentation of sleep and circadian studies.

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.

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.

Effects of sex and gender on adaptation to space: behavioral health

This article is part of a larger body of work entitled, "The Impact of Sex and Gender on Adaptation to Space." It was developed in response to a recommendation from the 2011 National Academy of Sciences Decadal Survey, "Recapturing a Future for Space Exploration: Life and Physical Sciences for a New Era," which emphasized the need to fully understand sex and gender differences. In this article, our workgroup-consisting of expert scientists and clinicians from academia and the private sector-investigated and summarized the current body of published and unpublished human research performed to date related to sex- and gender-based differences in behavioral adaptations to human spaceflight. This review identifies sex-related differences in: (1) sleep, circadian rhythms, and neurobehavioral measures; (2) personality, group interactions, and work performance and satisfaction; and (3) stress and clinical disorders. Differences in these areas substantially impact the risks and optimal medical care required by space-faring women. To ensure the health and safety of male and female astronauts during long-duration space missions, it is imperative to understand the influences that sex and gender have on behavioral health changes occurring during spaceflight.

Distribution of Chronotypes among a Sample of Iraqi Kurdish Medical Students

OBJECTIVES

The aim of this study was to assess the distribution of chronotypes in a sample of Iraqi Kurdish medical students.

METHODS

A descriptive cross-sectional study was conducted at the Hawler Medical University College of Medicine in Erbil City, Iraq, between 1(st) January and 31(st) March 2013. A total of 580 students were given the reduced version of the Horne and Ostberg Morningness-Eveningness Questionnaire (MEQr), a close-ended self-administered questionnaire.

RESULTS

Of the 580 students, 130 (22.4%) were male and 450 (77.6%) were female. The mean age ± standard deviation was 20.3 ± 1.45 years, with a range of 17-24 years. Most of the students (52.6%) were in the intermediate class, followed by morning type (24.1%) and evening type (23.3%). Significant gender differences were detected in the proportion of morning, intermediate and evening types (P <0.001). The mean scores for the female students were 14.8 ± 2.2 and the mean scores for the male students were 14.6 ± 7.3, with no statistically significant differences (P = 0.45).

CONCLUSION

Students in the College of Medicine were mostly classified as intermediate types. The morning type was more common among this student population, particularly male students, than has been reported in similar age groups in some Western countries. There was a significant gender difference in the proportion of MEQr types.

Chronotype ontogeny related to gender

Chronotype is an established concept designed to identify distinct phase relationships between the expression of circadian rhythms and external synchronizers in humans. Although it has been widely accepted that chronotype is subjected to ontogenetic modulation, there is no consensus on the interaction between age and gender. This study aimed to determine the relationship between age- and gender-related changes in the morningness-eveningness character in a large sample of people. A total of 14,650 volunteers were asked to complete the Brazilian version of the Horne and Östberg chronotype questionnaire. The data demonstrated that, on average, women were more morning-oriented than men until the age of 30 and there were no significant differences between men and women from 30 to 45 years of age. In contrast to the situation observed until the age of 30, women older than 45 years were more evening-oriented than men. These results suggest that the ontogenetic development of the circadian timekeeping system is more plastic in men, as represented by the larger amplitude of chronotype changes throughout their aging process. The phase delay of adolescence and phase advance of the elderly seem to be phenomena that are more markedly present in men than in women. Thus, our data, for the first time, provide support that sharply opposes the view that there is a single path toward morningness as a function of age, regardless of gender.