The epidemiology of morningness/eveningness: influence of age, gender, ethnicity, and socioeconomic factors in adults (30-49 years)

The Horne and Ostberg Morningness/Eveningness Questionnaire (MEQ) is widely used to differentiate between morning and evening types, but there is very little epidemiological evidence about the distribution of MEQ chronotypes in the general population. The purpose of the present study was to simultaneously investigate the influence of demographic, socioeconomic, and work factors on the distribution of morningness/eveningness. A New Zealand version of the MEQ was mailed to 5000 New Zealand adults, ages 30 to 49 years, who were randomly selected from the electoral rolls (55.7% response rate). A total of 2526 questionnaires were included in the analyses. According to the Horne and Ostberg classification, 49.8% of the total population was classified as morning type compared to 5.6% having an evening-type preference. However, using new cutoffs for middle-aged working adults described by Taillard et al. (2004), 24.7% of the population was morning type and 26.4% was evening type. After controlling for ethnicity, gender, and socioeconomic deprivation, participants ages 30 to 34 years were more likely to be definitely evening type (odds ratio [OR] = 1.59, p < 0.05) and less likely to be morning type (moderately morning type, OR = 0.59, p < 0.01, or definitely morning type, OR = 0.59, p < 0.05) compared to those ages 45 to 49 years. Work schedules were also important predictors of chronotype, with night workers more likely to be definitely evening type (OR = 1.49, p = 0.05) and the unemployed less likely to be moderately morning type (OR = 0.64, p < 0.05) compared to other workers. Evening types were 2.5 times more likely to report that their general health was only poor or fair compared to morning types (p < 0.01). This study confirms that the original criteria of Horne and Ostberg (1976) are not useful for classifying chronotypes in a middle-aged population. The authors conclude that morningness/eveningness preference is largely independent of ethnicity, gender, and socioeconomic position, indicating that it is a stable characteristic that may be better explained by endogenous factors.     

Reliability and validity of the Korean version of Morningness–Eveningness Questionnaire in adults aged 20–39 years

Morningness–Eveningness (ME) can be defined by the difference in individual diurnal preference observed from general behavioral patterns including sleep habits. The Horne & Östberg Morningness–Eveningness Questionnaire (MEQ) has been used for classifying ME types. We examined the reliability of a Korean version of the MEQ (Korean MEQ) and verified its validity by comparing responses on the Korean MEQ to objectively-recorded sleep–wake rhythms. After translating and back translating the MEQ from English into Korean, we examined the internal consistency of 19 items of the Korean MEQ in 91 subjects, and the test–retest reliability in 21 subjects who took the Korean MEQ twice, 4 weeks apart. The Korean MEQ was then administered to 1022 young adult subjects. A subset of 46 morning, neither, and evening type subjects took part in a validation study in which their rest-activity timing was collected by actigraphy for 7 days. Cosinor analyses on these data were done to obtain the acrophase and amplitude of the sleep–wake rhythm. Cronbach’s alpha of the total scores from the Korean MEQ was 0.77, and the test–retest reliability intra-class correlation coefficient was 0.90 (p?<?0.0001). There was a significant negative correlation between Korean MEQ score and reported sleep–wake timing among the entire cohort (p?<?0.0001). There was a significant difference in bedtime and wake time (on both work and free days), and in the mean sleep–wake rhythm acrophase, between ME types (p?<?0.01). In this study, the validity of the Korean MEQ was verified by illustrating the difference in acrophases of the sleep–wake rhythm between the ME types in young adults.     

The association between sleep chronotype and obesity among black and white participants of the Bogalusa Heart Study

ABSTRACT

Research indicates that sleep duration and quality are inter-related factors that contribute to obesity, but few studies have focused on sleep chronotype, representing an individual’s circadian proclivity, nor assessed these factors in racially diverse middle-aged samples. We examined the associations between chronotype and obesity among black and white men and women participating in the Bogalusa Heart Study (BHS).

Body mass index (BMI) and sleep data were available for 1,197 middle-aged men and women (mean age 48.2 ± 5.3 years) who participated in the BHS 2013–2016. Based on the reduced Morningness-Eveningness Questionnaire’s cutoff values for chronotypes, we combined ‘definitely morning’ and ‘moderately morning’ types into ‘morning’ type, ‘definitely evening’ and ‘moderately evening’ types into ‘evening’ type and kept those who were “neither” type in a separate group. We used ‘morning’ type as the referent group. Obesity was defined as a BMI ≥ 30. Multivariable logistic regression models were used to examine associations adjusting for sex, age, education, smoking, alcohol use and drug use, depression, shift work, physical activity and sleep duration.

Evening chronotype, reported by 11.1% of participants, was associated with obesity after multi-variable adjustment, including shift work, physical activity and sleep duration (OR 1.67, 95% CI: 1.08–2.56). However, once stratified by race (black/white), this association was found only among white participants (OR = 1.91, 95% CI = 1.12–3.25) after full adjustment.

In our biracial, community-based population, evening chronotype was independently associated with obesity, specifically among white participants. Further research is needed to identify behavioral, endocrine, nutritional and genetic pathways which underlie these associations.     

Ethnic differences in sleep duration and morning–evening type in a population sample

This cross-sectional population study examined associations of sleep duration and morning–evening type with sociodemographic and cardiometabolic disease in adults participating in the UK Biobank study (N = 439 933). Multivariable Poisson regression models of sleep duration and morning–evening type with a robust error variance were generated to estimate adjusted prevalence ratios and their 95% confidence intervals. All models were adjusted for sex, race, college attendance, employment status and age. Twenty five percent of the sample reported short sleep; 27% were morning, 64% intermediate and 9% evening type. Black ethnicity emerged as most strongly associated with sleep behavior. Short sleep was twice as prevalent, and morning versus intermediate type was 1.4 times more prevalent in Black than White participants. The greater prevalence of short sleep and morning type among Blacks suggests that sleep-based approaches to improving cardiometabolic outcomes may require a more multidimensional approach that encompasses adequate sleep and circadian alignment in this population.     

Role of patient chronotype on circadian pattern of myocardial infarction: a pilot study

Population-based studies indicate the risk of acute myocardial infarction (AMI) is greatest in the morning, during the initial hours of diurnal activity. The aim of this pilot study was to determine whether chronotype, i.e., morningness and eveningness, impacts AMI onset time. The sample comprised 63 morning- and 40 evening-type patients who were classified by the Horne-?stberg Morningness-Eveningness Questionnaire (MEQ) in the hospital after experiencing the AMI. The average wake-up and bed times of morning types were ~2?h earlier than evening types. Although the lag in time between waking up from nighttime sleep and AMI onset during the day did not differ between the two chronotypes, the actual clock-hour time of the peak in the 24-h AMI pattern did. The peak in AMI of morning types occurred between 06:01 and 12:00?h and that of the evening types between 12:01 and 18:00?h. Although the results of this small sample pilot study suggest one's chronotype influences the clock time of AMI onset, larger scale studies, which also include assessment of 24-h patterning of events in neither types, must be conducted before concluding the potential influence of chronotype on the timing of AMI onset.     

Morning-evening preference: sleep pattern spectrum and lifestyle habits among Japanese junior high school pupils

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

Role of Patient Chronotype on Circadian Pattern of Myocardial Infarction: A Pilot Study

Population-based studies indicate the risk of acute myocardial infarction (AMI) is greatest in the morning, during the initial hours of diurnal activity. The aim of this pilot study was to determine whether chronotype, i.e., morningness and eveningness, impacts AMI onset time. The sample comprised 63 morning- and 40 evening-type patients who were classified by the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ) in the hospital after experiencing the AMI. The average wake-up and bed times of morning types were ～2?h earlier than evening types. Although the lag in time between waking up from nighttime sleep and AMI onset during the day did not differ between the two chronotypes, the actual clock-hour time of the peak in the 24-h AMI pattern did. The peak in AMI of morning types occurred between 06:01 and 12:00?h and that of the evening types between 12:01 and 18:00?h. Although the results of this small sample pilot study suggest one's chronotype influences the clock time of AMI onset, larger scale studies, which also include assessment of 24-h patterning of events in neither types, must be conducted before concluding the potential influence of chronotype on the timing of AMI onset. (Author correspondence: dryavuzselvi@yahoo.com).     

Influence of chronotype, season, and sex of subject on sleep behavior of young adults

The aim of this study was to investigate whether sex, season, and/or chronotype influence the sleep behavior of university students. Detailed data were collected on activity/rest patterns by wrist actigraphy combined with diaries. Thirty-four medical students (19 female and 15 male) were monitored by Actiwatch actometers for 15 consecutive days in May and again in November. The data of a modified Horne and Ostberg chronotype questionnaire, which were collected from 1573 female and 1124 male medical school students surveyed in the spring and autumn over an eight-year period, were evaluated. Actiwatch sleep analysis software was used to process the activity data with statistical analyses performed with ANOVA. We found no significant sex-specific differences in sleep efficiency, sleep onset latency, or actual sleep-time duration. However, we did find a difference in sleep efficiency between morning and evening types, with morning types having a higher sleep efficiency (87.9%, SD=1.3) than evening types (84.3%, SD=0.87%; p=0.007). Seasonal differences were also detected: the actual sleep-time duration in autumn was significantly longer (mean 6.9 h, SD=0.13 h) than in spring (6.6 h, SD=0.1 h; p=0.013). Evaluation of the chronotype questionnaire data showed that individuals with no special preference for morningness or eveningness (i.e., so-called intermediates) were most common. The distribution of chronotypes was related to the sex of subject. Men displayed eveningness significantly more often than women (28.9% males vs. 20.8% females; p<0.001), while females exhibited greater morningness (20.3% females vs.15.6% males; p<0.001). Sex influences chronotype distribution, but not actual sleep time-duration, sleep onset latency, or sleep efficiency. The latter, however, differed among chronotypes, while actual sleep-time duration was affected by season.     

Chronotype and Breast Cancer Risk in a Cohort of US Nurses

The aim of this study was to examine the relation between chronotype and breast cancer risk. We analyzed the association between chronotype (definite morning type, probable morning type, probable evening type, definite evening type, or neither morning nor evening type) and breast cancer risk among 72 517 women in the Nurses’ Health Study II (NHS II). Chronotype was self-reported in 2009, and 1834 breast cancer cases were confirmed among participants between 1989 and 2007; a 2-yr lag period was imposed to account for possible circadian disruptions related to breast cancer diagnosis. Age- and multivariable-adjusted logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Participants who self-reported as neither morning nor evening type had a 27% increased risk of breast cancer (multivariable-adjusted OR?=?1.27, 95% CI?=?1.04–1.56), compared with definite morning types. None of the other chronotypes were significantly associated with breast cancer risk (multivariable-adjusted OR?=?0.99, 95% CI?=?0.87–1.12 for probable morning versus definite morning types; OR?=?0.96, 95% CI?=?0.84–1.09 for probable evening versus definite morning types; and OR?=?1.15, 95% CI?=?0.98–1.34 for definite evening versus definite morning types). Overall, chronotype was not associated with breast cancer risk in our study. A modestly increased risk among neither morning nor evening types may indicate circadian disruption as a potentially underlying mechanism; however, more studies are needed to confirm our results.     

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

The Circadian Energy Scale (CIRENS): two simple questions for a reliable chronotype measurement based on energy

This study presents the Circadian Energy Scale (CIRENS), a very short and simple chronotype measurement tool based on energy. The CIRENS consists of two introspective questions about the usual energy level (very low, low, moderate, high, or very high, scored 1 to 5) in the morning and in the evening. The difference between energy level scores (-4 to 4) felt by respondents in the evening and morning defines the chronotype score and classification. A concurrent validity analysis of the CIRENS with the widely used Horne and ?stberg Morningness-Eveningness Questionnaire (MEQ) was conducted using a sample of 225 college students, and with MSFsc, a sleep-based chronotype assessment tool based on the Munich Chronotype Questionnaire (MCTQ), using a sample of 34,530 subjects (18-83 yrs, 27% males). This large sample was collected in a Web survey for behavioral correlates of the CIRENS with variables previously associated with chronotype differences. The correlation of the CIRENS chronotype score was r?=?-.70 with the MEQ and r?=?.32 with the MSFsc. CIRENS chronotype scores declined with age and were not affected by sex. Both CIRENS and MSFsc chronotype scores were related to differences in tobacco, caffeine, and cola soft-drink consumption (all higher in evening types). The CIRENS provides a simple chronotype index and a measure of absolute energy throughout the day and seems to be a reliable chronotype assessment tool that may be useful both clinically and for large-scale studies.     

Evening typology and morning tiredness associates with low leisure time physical activity and high sitting

Circadian typology is a latent trait that is usually assessed with scoring on a series of questions thought to represent the construct. But, in the classification, most people fall into the intermediate type, i.e. neither a definite morning nor an evening type, but still showing stronger preference towards either end of the continuum. Our aim was to operationalize chronotype using latent class analysis (LCA) for a 6-item scale derived from the original Horne–Östberg Morningness–Eveningness Questionnaire to compare and understand characteristics of chronotype in a population-based sample of adults in Finland. A total of 4904 men and women aged 25–74 years were included. We also analyzed the associations of chronotypes with physical activity (PA) and sitting. We found five latent chronotype groups including “rested more-evening type” (28%), “rested more-morning type” (24%), “morning type” (23%), “tired more-evening type” (17%) and “evening type” (8%) groups. Operationalization of chronotype by LCA suggests that morning alertness is an important feature differentiating chronotypes. Further, the “evening type” and the “tired, more-evening type” had higher odds for none to very low as well as low PA, as compared to “morning type”. In addition, “evening type” was associated with higher odds for more time spent sitting, as compared to “morning type”. Our findings indicate that it is important to assess sleep schedules and morning tiredness, which then could be targeted as a potential mediating factor for health behaviors, in particular, PA and health status.     

The relationship between chronotype,sleep disturbance,severity of fibromyalgia,and quality of life in patients with fibromyalgia

ABSTRACT

Patients with fibromyalgia (FM) report high levels of sleep disturbance and chronic diffuse musculoskeletal pain. These patients experience diminished quality of life (QoL) due to pain and other comorbidities. Chronotype preferences have been suggested as a potential factor connecting increased severity of FM, sleep disturbances, and poor overall QoL. The present study is the first study examining the possible association between chronotype preferences, sleep disturbance, severity of FM, and QoL in patients with FM.

One hundred drug-free patients diagnosed with FM participated in this cross-sectional study. Of them, 79 (79%) were females and 21 (21%) were males. The mean age was 41.65 ± 9.17 years (range: 21–62 years). The severity of FM symptoms, chronotype preferences, and QoL was evaluated using the Fibromyalgia Impact Questionnaire (FIQ), Morningness-Eveningness Questionnaire (MEQ), and World Health Organization Questionnaire on Quality of Life: Short Form (WHOQOL-BREF). The participants’ anxiety/depressive symptoms and sleep problems were assessed using the Hospital Anxiety and Depression Scale (HADS) and Pittsburgh Sleep Quality Index (PSQI).

The participants were classified according to their MEQ scores as evening type (score: 16–41), neither type (score: 42–58), and morning type (score: 59–86). It was found that there were significant differences in the FIQ score between the three groups (p < .001). It was determined that the total PSQI score was significantly higher in the evening type than the other two types (p < .05). It was found that there were significant differences in the general health, physical health, psychological, and environmental domain scores of the WHOQOL-BREF between the three groups (p < .05). It was detected that there were significant correlations between MEQ scores, WHOQOL-BREF subscale scores, FIQ scores, HADS-A and HADS-D scores, and PSQI scores. According to hierarchical regression analysis, eveningness preference explained an additional 21.9% of the variation in FM severity, thereby causing a statistically significant change in R-squared.

Our results indicated that eveningness preference was directly related to increased FM symptom severity and poorer QoL. Based on these findings, neglecting to take chronotype preference into account may not result in optimal response to standard treatment for some patients with FM.     

Evening chronotype is associated with poor cardiovascular health and adverse health behaviors in a diverse population of women

ABSTRACT

Chronotype reflects time of day preferences for performing daily activities. Previous research within Asian and European cohorts indicates evening chronotype is associated with elevated cardiometabolic risk. However, evidence is limited from population-based US cohorts, particularly among women in whom evening chronotype prevalence may become higher after middle-age, coinciding with life stages associated with higher cardiovascular disease (CVD) risk. This cross-sectional study evaluated associations of chronotype with overall cardiovascular health (CVH), health behaviors, and cardiometabolic risk factors among 506 women (mean age = 37 ± 16y, 62% racial/ethnic minority) in the American Heart Association (AHA)’s Go Red for Women Strategically-Focused Research Network cohort at Columbia University (New York City, NY, USA). Chronotype was assessed using the validated Morningness-Eveningness Questionnaire (MEQ) and categorized as “evening”, “intermediate”, and “morning” chronotypes. Health behaviors (diet, physical activity, and sleep) were assessed using validated questionnaires. Anthropometrics, clinical blood pressure, and blood biomarkers were assessed at the clinic visit. CVH was evaluated using the AHA Life’s Simple 7 (LS7) metrics; LS7 scores of 0–8 and 9–14 were considered indicative of poor and moderate-to-high CVH, respectively. Linear and logistic regression models adjusted for age, race/ethnicity, education, health insurance, and menopausal status were used to examine associations of MEQ scores and chronotype categories with overall CVH, clinical cardiometabolic risk factors, and health behaviors. Overall, 13% of women identified as evening chronotypes, while 55% and 32% reported being intermediate and morning types. In linear models, higher MEQ scores were associated with higher AHA LS7 scores (β(SE) = 0.02(0.01); p = .014), indicative of more favorable CVH, and with health behaviors not included in the LS7. Higher MEQ scores were also associated with lower Pittsburgh Sleep Quality Index, i.e. better sleep quality, (β(SE) = ?0.07(0.02), p < .0001), lower insomnia severity (β(SE) = ?0.14(0.01), p < .0001), shorter time to fall asleep (β(SE) = ?0.28(0.14), p = .044), and less sedentary time (β(SE) = ?0.11(0.03), p = .001). In logistic regression models, evening chronotype, compared to intermediate/morning type, was associated with higher odds of having poor CVH (OR(95%CI):2.41(1.20–4.85)), not meeting AHA diet (OR(95%CI):2.89(1.59–5.23)) and physical activity guidelines (OR(95%CI):1.78(1.03–3.07)), and having short sleep (OR(95%CI):2.15(1.24–3.73)) or insomnia (OR(95%CI):2.69(1.53–4.75)). The evening type compared to morning type was also associated with being a current smoker (OR(95%CI):2.14(1.02–4.52)) and having poor sleep quality (OR(95%CI:2.35(1.27–4.37)) and long sleep onset latency (OR(95%CI:1.89(1.00–3.56)). In our cohort of women, evening chronotype was related to poor CVH, likely driven by its influence on health behaviors. These findings, although warranting confirmation prospectively in other populations, suggest chronotype is an important factor to consider and possibly target when designing lifestyle interventions for CVD prevention.     

Evening preference is related to the incidence of depressive states independent of sleep-wake conditions

Although evening preference has recently been identified as a risk factor for depression, it has not been substantiated whether evening preference is a direct risk factor for depressive states, or if it is associated secondarily through other factors, such as delayed sleep timing and shortened sleep duration. The objective of this study is to investigate associations in Japanese adult subjects between evening preference and incidence of depressive states, adjusting for various sleep parameters related to depressive states. The Morningness-Eveningness Questionnaire (MEQ), the Pittsburgh Sleep Quality Index (PSQI), and the Center for Epidemiologic Studies Depression Scale (CES-D) were administered to 1170 individuals (493 males/677 females; mean and range 38.5 and 20-59 yrs) to assess their diurnal preferences, sleeping states, and presence of depression symptoms. Subjects were classified into five chronotypes based on MEQ scores. Evening preference was associated with delayed sleep timing, shortened sleep duration, deteriorated subjective sleep quality, and worsened daytime sleepiness. Logistic regression analysis demonstrated that the extreme evening type (odds ratio [OR]?=?1.926, p?=?.018) was associated with increased incidence of depressive states and that the extreme morning type (OR?=?0.342, p?=?.038) was associated with the decreased incidence of depressive states, independent of sleep parameters, such as nocturnal awakening (OR?=?1.844, p?相似文献   

Effect of circadian rhythm type on serum lipid levels in shift workers: A 5-year cohort study

We investigated how differences in circadian rhythm type affect the health of workers engaged in shift work. Employees, who were newly hired in a steel company between 2007 and 2011, received the Morningness–Eveningness Questionnaire (MEQ) survey. The target participants were 153 male shift workers who were not being treated with any antihyperlipidemic drugs and underwent periodic physical examinations including blood tests at least twice. According to the score of the MEQ at the time of joining the company, we classified the subjects into five types. Longitudinal changes in serum lipid level were estimated among the circadian rhythm types adjusted for age, BMI, and other covariates using a linear mixed model. The regression coefficient of total cholesterol level in the “definitely and moderately morning” group was ?17.83 (95% confidence interval (CI): ?33.42 to ?2.23), and in the “intermediate ‘group’ was ?16.84 [95% CI: ?30.40 to ?3.28], compared to the moderate evening type.” The total cholesterol level was higher in the moderately evening type than in any of the other groups. Between the Morningness–Eveningness (ME) type and Low-density lipoprotein (LDL) cholesterol levels, compared with the “moderately evening type” group, the regression coefficient in the “intermediate type” group was ?16.08 (95% CI: ?28.79 to ?3.37), and in the “definitely and moderately morning type” group was ?17.50 [95% CI: ?32.11 to ?2.88]. The “moderately evening type” group had a higher LDL cholesterol level than any of the other groups. Evening-type circadian rhythm type shift workers are more prone to elevated serum lipid levels.     

Chronotype and postmenopausal breast cancer risk among women in the California Teachers Study

ABSTRACT

Chronotype is the behavioral manifestation of an individual’s underlying circadian rhythm, generally characterized by one’s propensity to sleep at a particular time during the 24 hour cycle. Evening chronotypes (“night owls”) generally suffer from worse physical and mental health compared to morning chronotypes (“morning larks”) – for reasons that have yet to be explained. One hypothesis is that evening chronotypes may be more susceptible to circadian disruption, a condition where the coordinated timing of biologic processes breaks down. The role of chronotype as an independent or modifying risk factor for cancer has not been widely explored. The objective of the current study was to evaluate the risk of breast cancer associated with chronotype in a case-control study nested within the California Teachers Study (CTS) cohort. The study population consisted of 39686 post-menopausal CTS participants who provided information on chronotype by completing a questionnaire in 2012–2013. 2719 cases of primary invasive breast cancer diagnosed from 1995/1996 through completion of the chronotype questionnaire were identified by linkage of the CTS to the California Cancer Registry. 36967 CTS participants who had remained cancer-free during this same time period served as controls. Chronotype was ascertained by responses to an abbreviated version of the Horne-Ostberg Morningness-Eveningness Questionnaire (MEQ) and was characterized into five categories: definite morning, more morning than evening, neither morning or evening, more evening than morning, definite evening. Multivariable unconditional logistic regression analyses were performed to estimate the odds ratios (ORs) and 95% confidence intervals (95% CIs) for each of the chronotypes, adjusted for established breast cancer risk factors. Compared to definite morning types, definite evening types had an increased risk of breast cancer with elevated ORs that were statistically significant in both the crude (OR = 1.24, 95% CI: 1.10–1.40) and fully-adjusted models (OR = 1.20, 95% CI: 1.06–1.35). The risk estimates in the fully-adjusted model for all other chronotypes did not significantly differ from one. These results suggest that evening chronotype may be an independent risk factor for breast cancer among a population of women who are not known to have engaged in any substantial night shift work. Further research in other populations of non-shift workers is warranted.     

Differences in morning–evening type and sleep duration between Black and White adults: Results from a propensity-matched UK Biobank sample

Biological evidence suggests that ethno-racial differences in morning–evening type are possible, whereby Blacks may be more likely to be morning type compared to Whites. However, population-level evidence of ethno-racial difference in morning–evening type is limited. In an earlier study, we reported that morning type was more prevalent in Blacks compared to Whites in the United Kingdom (UK) Biobank cohort (N = 439 933). This study aimed to determine if these ethno-racial differences persisted after accounting for an even broader range of social, environmental and individual characteristics and employing an analytic approach that simulates randomization in observational data, propensity score modeling. Data from UK Biobank participants whose self-identified race/ethnicity was Black/Black British or White; who did not report daytime napping, shift work or night shift work; who provided full mental health information; and who were identified using propensity score matching were used (N = 2044). Each sample was strongly matched across all social, environmental and individual characteristics as indicated by absolute standardized mean differences <0.09 for all variables. The prevalence of reporting nocturnal short, adequate and long sleep as well as morning, intermediate and evening type among Blacks (n = 1022) was compared with a matched sample of Whites (n = 1022) using multinomial logistic regression models. Blacks had a 62% greater odds of being morning type [odds ratio (OR) = 1.620, 95% confidence interval (CI): 1.336–1.964, p < .0001] and a more than threefold greater odds of reporting nocturnal short sleep (OR = 3.453, 95% CI: 2.846–4.190, p < .0001) than Whites. These data indicate that the greater prevalence of morning type and short nocturnal sleep in Blacks compared to Whites is not fully explained by a wide range of social and environmental factors. If sleep is an upstream determinant of health, these data suggest that ethno-racially targeted public health sleep intervention strategies are needed.     

The Circadian Energy Scale (CIRENS): Two Simple Questions for a Reliable Chronotype Measurement Based on Energy

This study presents the Circadian Energy Scale (CIRENS), a very short and simple chronotype measurement tool based on energy. The CIRENS consists of two introspective questions about the usual energy level (very low, low, moderate, high, or very high, scored 1 to 5) in the morning and in the evening. The difference between energy level scores (?4 to 4) felt by respondents in the evening and morning defines the chronotype score and classification. A concurrent validity analysis of the CIRENS with the widely used Horne and Östberg Morningness-Eveningness Questionnaire (MEQ) was conducted using a sample of 225 college students, and with MSFsc, a sleep-based chronotype assessment tool based on the Munich Chronotype Questionnaire (MCTQ), using a sample of 34,530 subjects (18–83 yrs, 27% males). This large sample was collected in a Web survey for behavioral correlates of the CIRENS with variables previously associated with chronotype differences. The correlation of the CIRENS chronotype score was r?=??.70 with the MEQ and r?=?.32 with the MSFsc. CIRENS chronotype scores declined with age and were not affected by sex. Both CIRENS and MSFsc chronotype scores were related to differences in tobacco, caffeine, and cola soft-drink consumption (all higher in evening types). The CIRENS provides a simple chronotype index and a measure of absolute energy throughout the day and seems to be a reliable chronotype assessment tool that may be useful both clinically and for large-scale studies. (Author correspondence: diogorlara@gmail.com)     

Differences in circadian phase and weekday/weekend sleep patterns in a sample of middle-aged morning types and evening types

Factors contributing to sleep timing and sleep restriction in daily life include chronotype and less flexibility in times available for sleep on scheduled days versus free days. There is some evidence that these two factors interact, with morning types and evening types reporting similar sleep need, but evening types being more likely to accumulate a sleep debt during the week and to have greater sleep extension on weekend nights. The aim of the present study was to evaluate the independent contributions of circadian phase and weekend-to-weekday variability to sleep timing in daily life. The study included 14 morning types and 14 evening types recruited from a community-based sample of New Zealand adults (mean age 41.1 ± 4.7 years). On days 1–15, the participants followed their usual routines in their own homes and daily sleep start, midpoint and end times were determined by actigraphy and sleep diaries. Days 16–17 involved a 17 h modified constant routine protocol in the laboratory (17:00 to 10:00, <20 lux) with half-hourly saliva samples assayed for melatonin. Mixed model ANCOVAs for repeated measures were used to investigate the independent relationships between sleep start and end times (separate models) and age (30–39 years versus 40–49 years), circadian phase [time of the dim light melatonin onset (DLMO)] and weekday/weekend schedules (Sunday–Thursday nights versus Friday–Saturday nights). As expected on weekdays, evening types had later sleep start times (mean = 23:47 versus 22:37, p < .0001) and end times (mean = 07:14 versus 05:56, p < .0001) than morning types. Similarly on weekend days, evening types had later sleep start times (mean = 00:14 versus 23:07, p = .0032) and end times (mean = 08:56 versus 07:04, p < .0001) than morning types. Evening types also had later DLMO (22:06 versus 20:46, p = .0002) than morning types (mean difference = 80.4 min, SE = 18.6 min). The ANCOVA models found that later sleep start times were associated with later DLMO (p = .0172) and weekend-to-weekday sleep timing variability (p < .0001), after controlling for age, while later sleep end times were associated with later DLMO (p = .0038), younger age (p = .0190) and weekend days (p < .0001). Sleep end times showed stronger association with DLMO (for every 30 min delay in DLMO, estimated mean sleep end time occurred 14.0 min later versus 10.19 min later for sleep start times). Sleep end times also showed greater delays on weekends versus weekdays (estimated mean delay for sleep end time = 84 min, for sleep start time = 28 min). Comparing morning types and evening types, the estimated contributions of the DLMO to the mean observed differences in sleep timing were on weekdays, 39% for sleep start times and 49% for sleep end times; and on weekends, 41% for sleep start times and 34% of sleep end times. We conclude that differences in sleep timing between morning types and evening types were much greater than would be predicted on the basis of the independent contribution of the difference in DLMO on both weekdays and weekend days. The timing of sleep in daily life involves complex interactions between physiological and psychosocial factors, which may be moderated by age in adults aged 30–49 years.