Metrics details 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 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 in spite of universal access to electricity the Baependi population was strongly shifted towards morningness Heritability of MEQ score was 0.48 when adjusted for sex and age The reported MEQ score heritability is more akin to those of previous twin studies than previous family studies The study has gradually grown to encompass a wider range of phenotypes related to health and well-being Histogram showing the distribution of MEQ score in the Baependi population The black section of each bar for each score represents the frequency in the rural zone and the remainder in the municipal zone Low scores represent evening types and high scores morning types Histogram showing the distribution of MEQ score in the pooled Baependi population (black bars) contrasted with the distribution in the pooled data from two studies performed at the London Science Museum (dark grey bars) and one study performed within residents of the city of São Paulo (light grey bars) Distribution of MEQ score in the pooled Baependi population as a function of age. Normality plot of MEQ score distribution in the Baependi population The high degree of normality across the medium and lower range of the scale is distorted at the highest range The estimates of heritability (h2 ± standard error) are shown in Table 2 The heritability estimate for MEQ was 0.21 in the unadjusted or reduced mixed model the inclusion of age and gender as covariates raised this value to 0.48 The added inclusion of age × age and age × gender did not change this value gender and municipal versus rural residence were all added as covariates the average age in the Baependi study was 46.4 years Our data suggest that some of the options offered for some of the answers do not accommodate the actual preference of an individual whose phase is more attuned to solar time our participants tried to modify these answers for example the answer to Question 1 ("Approximately what time would you get up if you were entirely free to plan your day?") where they indicated that the earliest option offered (0500) was later than their actual preference Whilst these family studies were also performed in close-knit (and inbred) communities showing extreme morningness both communities are based on adherence to anabaptist faith principles where the use of electrically powered devices including television is limited intrinsic diurnal preference was being masked within a well-defined cohort such as the Baependi one there is a significant heritable dimension to the MEQ score that would make the GWAS approach feasible The study protocol conformed to the tenets of the Declaration of Helsinki and was approved by the ethics committee of the Hospital das Clínicas Each subject provided informed written consent before participation probands were selected at random across 11 out of the 12 census districts in Baependi nephews/nieces and double cousins) and third-degree (first cousins great uncles/aunts and great nephews/nieces) relatives and his/her respective spouse's relatives resident both within Baependi (municipal and rural area) and surrounding towns were invited to participate Only individuals age 18 and older were eligible to participate in the study The study is conducted from a clinic/office in an easily accessible sector of the town The questionnaire was completed in hard copy format either by the participant or by a trained scribe A small number of omissions of answers to single questions were rectified by telephoning the participant and repeating the question Answers to individual questions were entered in a database together with the subject's age at the time gender and residence within the municipal or the rural zone of the town Where residential zone was not explicitly noted as part of the address the presence or absence of a street with a number was used to determine whether the participant was resident in the municipal or the rural zone precision and near-24-hour period of the human circadian pacemaker Strain differences of the mouse's free-running circadian rhythm in continuous darkness Circadian timekeeping in BALB/c and C57BL/6 inbred mouse strains Heritable circadian period length in a wild bird population Familial advanced sleep-phase syndrome: A short-period circadian rhythm variant in humans A mutation of the circadian system in golden hamsters Bright light resets the human circadian pacemaker independent of the timing of the sleep-wake cycle Age-related change in the relationship between circadian period circadian phase and diurnal preference in humans The circadian and homeostatic modulation of sleep pressure during wakefulness differs between morning and evening chronotypes Circadian and homeostatic sleep regulation in morningness-eveningness PER3 polymorphism predicts sleep structure and waking performance The 3111Clock gene polymorphism is not associated with sleep and circadian rhythmicity in phenotypically characterized human subjects A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms Circadian Typology: A comprehensive review limits and applicability of the main instruments used in the literature to assess human phenotype Instituto Brasileiro de Geografia e Estastística. Census data (http://censo2010.ibge.gov.br/) (2010) Heritability of cardiovascular risk factors in a Brazilian population: Baependi Heart Study Age-related change in the association between a polymorphism in the PER3 gene and preferred timing of sleep and waking activities Sleep-wake cycle expression in adolescence: Influences of social context Differences in circadian patterns between rural and urban populations: an epidemiological study in countryside Habitual sleep/wake patterns in the Old Order Amish: heritability and association with non-genetic factors Impact of lifestyle on circadian orientation and sleep behaviour Clocks for the city: circadian differences between forest and city songbirds Entrainment of the human circadian clock to the natural light-dark cycle Horne and Ostberg questionnaire: A score distribution in a large sample of young adults Gender differences in morningness-eveningness preference Validation of Horne and Ostberg morningness-eveningness questionnaire in a middle-aged population of French workers Diurnal preference and sleep quality: same genes Genetic analysis of morningness and eveningness Genetic and environmental influence on morningness-eveningness Heritability of diurnal type: a nationwide study of 8753 adult twin pairs Heritability of morningness-eveningness and self-report sleep measures in a family-based sample of 521 hutterites A CLOCK polymorphism associated with human diurnal preference A length polymorphism in the circadian clock gene Per3 is linked to delayed sleep phase syndrome and extreme diurnal preference A single-nucleotide polymorphism in the 5'-untranslated region of the hPER2 gene is associated with diurnal preference A silent polymorphism in the PER1 gene associates with extreme diurnal preference in humans A novel SNP in hPer2 associates with diurnal preference in a healthy population Polymorphism in the PER3 promoter associates with diurnal preference and delayed sleep phase disorder Screening of Clock Gene Polymorphisms Demonstrates Association of a PER3 Polymorphism with Morningness-Eveningness Preference and Circadian Rhythm Sleep Disorder Schizophrenia Working Group of the Psychiatric Genomics Consortium Biological insights from 108 schizophrenia-associated genetic loci Exploration of transcultural properties of the reduced version of the Morningness–Eveningness Questionnaire (rMEQ) using adaptive neuro-fuzzy inference system 955–968; 10.1080/09291016.2014.939442 (2014) in XIX International Conference of the International Society for Chronobiology Methods to estimate genetic components of variance for quantitative traits in family studies 10.1002/(SICI)1098-2272(1999)17:1&lt;64::AID-GEPI5&gt;3.0.CO;2-M (1999) quantity and age-at-onset of regular cigarette use in Brazilian families: the Baependi Heart Study Variance component methods for analysis of complex phenotypes Multipoint quantitative-trait linkage analysis in general pedigrees Download references This work was performed at the University of São Paulo It was supported by an international visiting professorship grant from the University of São Paulo (awarded to JEK on behalf of MvS) by Fapesp grants 2013/17368-0 (to ACP) and 2011/05804-5 (to MP) by CNPq grant 400791/2015-5 (to HV) and by a Banco Santander travel award (to MvS) We are grateful to the study participants for their voluntary and unrewarded participation in this study and to the study staff in the Corações de Baependi office We also wish to thank Jason Ellis for sharing his spreadsheet template and to Simon N Archer for permission to show data collected in a previous collaboration Laboratory of Genetics and Molecular Cardiology Department and Institute of Psychiatry (LIM 23) The authors declare no competing financial interests Download citation Anyone you share the following link with will be able to read this content: a shareable link is not currently available for this article Sign up for the Nature Briefing newsletter — what matters in science Metrics details It has been hypothesised that contemporary urban populations are under pressure towards shorter sleep duration and poorer sleep quality Baependi is a small town in Brazil that provides a window of opportunity to study the influence of sleep patterns in a highly admixed rural population with a conservative lifestyle and chronotype using the Pittsburgh Sleep Quality Index Epworth Sleepiness Scale and Morningness-Eveningness Questionnaire questionnaires The sample consisted of 1,334 subjects from the Baependi Heart study (41.5% male; age: 46.5 ± 16.2 y Average self-reported sleep duration was 07:07 ± 01:31 (bedtime 22:32 ± 01:27 chronotype was 63.6 ± 10.8 and daytime sleepiness was 7.4 ± 4.8 Despite a shift towards morningness in the population chronotype remained associated with reported actual sleep timing Age and sex modulated the ontogeny of sleep and chronotype increasing age was associated with earlier sleep time and shorter sleep duration and reported poorer sleep quality than men (p < 0.0001) This study provides indirect evidence in support of the hypothesis that sleep timing was earlier prior to full urbanisation these communities also showed significant seasonal patterns and sleep timing was more likely to be associated with environmental temperature rather than with light (sunset or sunlight) there is no current strong consensus on the outcomes of urbanization on sleep patterns more data from a greater diversity of communities are needed The quantitative answers to PSQI allowed us to consider self-reported rise and bed times Table 1 describes the demographic characteristics of the sample The entire study sample was 1,847 subjects out of which 1,334 individuals were considered eligible for statistical comparisons Subjects missing data-points in one or more questionnaires were excluded from this analysis The age range of the sample was 18 to 89 years 31.7% of subjects presented excessive daytime sleepiness (scores equal or above 10 on the ESS) and 34.9% presented scores equal or above 5 on the Pittsburgh Sleep Quality Index (PSQI) meaning that their sleep quality was classified as poor Women had poorer self-reported sleep quality than men based on PSQI score (means ± standard deviation) (5.4 ± 3.3 vs 4.5 ± 2.9; p < 0.001 accounting for a small difference between the sexes more women had a PSQI score above 5 than men (39.9% vs 27.8% Women also presented later wake up times (means ± standard deviation (06:26 ± 01:17) vs (06:04 ± 01:34); p < 0.01 meaning that this difference between sexes was small Women spent more time in bed than men (means ± standard deviation (07:52 ± 1:26) vs (07:32±01:31) hour:min ± hour:min; p < 0.005 Self-reported sleep duration was longer in women than men (means ± standard deviation (07:13 ± 1:33) vs (06:57 ± 1:27) hour:min ± hour:min; p < 0.01); however the difference was small according to the Cohen’s d value of 0.10 Frequency distribution for PSQI category and components by sex Subjects with scores ≥5 were classified as having poor sleep quality A higher frequency of women presented poor sleep quality Χ2 = 20.80; p < 0.001 There was a sex effect on how subjects rated their sleep with women tending to declare poorer sleep quality X2 = 7.97; p < 0.05 (C) A higher proportion of women reported longer sleep latency X2 = 10.81; p < 0.05 (D) Sleep duration and (E) sleep efficiency no statistical difference between the sexes women were more prone to declare having sleep disturbances during the last month X2 = 20.37; p < 0.001; (G) Use of sleep medication: Men declared less use of sleep medication than women during the last month X2 = 29.95; p < 0.00 (H) Daytime dysfunction: A higher proportion of women declared having daytime dysfunction during the last month X2 = 44.89; p < 0.0001 Frequency distribution histograms for self-reported sleep patterns derived from the PSQI (1,334 subjects were included) The upper panel shows the entire population and the lower panel the same dataset divided by sex (A and D) show bedtime frequency distribution binned by 1-hour intervals from 19 h to after 04 h (B and E) show sleep duration frequency distribution binned by 1-hour intervals from 02 h to >11 h of sleep duration (C and E) show wake-up time frequency distribution binned by 1-hour intervals from 01 h to 11 h There was higher proportion of male subjects going to bed before 23 h χ2 = 32.83; p < 0.0001 (D) and a higher proportion of male subjects presenting earlier wake up times Χ2 = 45.87; p < 0.001 (F) Next, to evaluate the sleep patterns of this population, we extracted the information from the PSQI related to the timing and duration of sleep: Bedtime, sleep duration, and wake up time. Self-reported bedtime, wake up time, and sleep duration were plotted in frequency distribution histograms, (Fig. 2) The sleep timings confirmed the “early bird” pattern of the majority of the sample with a large proportion (48%) of subjects presenting bedtimes between 22 and 23 h and wake-up times between 05 and 06 h A large proportion (67%) of subjects also reported sleeping 7 or more hours which do not differ significantly between the sexes Sleep patterns according to chronotype Means and standard error of the mean for Bed time and Wake up time extracted from the PSQI E-types (N = 125) presented later bedtime in comparison to M-types (N = 97) and N-types (N = 830) subjects M-types subjects also went to bed earlier than N-types Bonferroni post-hoc comparisons for (a and b) produced p < 0.0001 E-types also presented later wake up time in comparison to M-types and N-types Bonferroni post-hoc comparison for (c) yielded p < 0.0001 To further evaluate the relationship between age and sex on sleep patterns and chronotype ontogeny, the sample was binned in 5 age groups (18–31y; 31–40y; 41–50y; 51–60y and 61 and up). Detailed information about the age groups is presented in Table S1 Age and sex influence sleep characteristics and chronotype Values are presented as means ± standard error (A) Self-reported sleep duration Bonferroni post hoc test indicated a difference between means of sleep duration at the youngest (18–30y) and the oldest age bins (61-up) for both sexes Bonferroni post hoc test suggested a significant advance in bedtime of men from the age bin 18–30y to the 31–40y when women presented later bedtimes Bonferroni post hoc test found significant differences between the youngest (18–30 years) to the second youngest (31–40 years) bins in both sexes with significant sex differences emerging for the age bin 51–60 years Bonferroni post hoc test indicated a significant difference between sexes for the youngest age bin (18–30 years) Bonferroni post-hoc testing yielded a statistically significant difference between sexes in the age bin 51–60y women presented increasingly poor sleep quality after 41–50 years in comparison to youngest age bin (18–30 years) Age and sex comparisons also were performed for sleepiness. Sleepiness scores did not change according to age (p = 0.076) or differ between sexes (p = 0.91); consequently, no interaction between factors was found (p = 0.09) (for means and standard error please see Table S1) E-types were significantly overrepresented amongst poor sleepers poor sleepers also presented later bedtimes (p < 0.001) spent less time in bed (p = 0.01) and had longer sleep latency (p < 0.001) than subjects classified with good sleep quality Chronotype was another important factor modulating sleep quality E-types presented poor sleep quality than M-types and N-types further evaluation of the association between menopause and sleep quality should be performed in this population there can be sex differences related to the way people respond to the questionnaire subjective sleep quality differs between men and women in this community but it can not be inferred from the observations made here whether the subjective sleep quality differences entirely reflect differences in objective sleep quality This study presents strengths and limitations worth mentioning We report subjective data based on questionnaires Although these instruments have been used for sleep research and in sleep clinics worldwide they contain measures that are subjected to considerable variation in the subject’s personal interpretation The life experience of Baependi residents may be uniquely reflected in some of their answers such as actimetry and circadian phase markers these datasets can be combined with the multiple layers of phenotype data from the Baependi study and be related to health outcomes and major risk factors The findings from this interesting cohort show that the presence of electrification does not obligately (or at least not immediately) lead to shifted chronotype distributions towards eveningness and chronotype and delayed sleep and wake timings They also indicate that an earlier sleep phase does not equate to a perception of better sleep they justify the further investigation of the environmental and lifestyle factors associated with these observations The longitudinal nature of the Baependi Heart Study will make it possible to investigate whether and how these parameters will change over future years The ESS produces a score from 0 to 24 and results equal or above 10 are considered excessive daytime sleepiness data from 1,334 individuals were considered complete and eligible for statistical comparisons Data from subjects with missing one or more answers for more than one questionnaire were excluded Data were analysed by comparison of means using Student’s t tests Age was considered as continuous variable for correlational analysis and the sample was binned into five age groups (18–30y 51–60y and 61- years) to perform mean comparisons Timing and quality of sleep in a rural Brazilian family-based cohort Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations Sleep duration predicts cardiovascular outcomes: A systematic review and meta-analysis of prospective studies Sleep duration and cardiometabolic risk: A review of the epidemiologic evidence Sick and tired: Does sleep have a vital role in the immune system The Role of Sleep in Cognition and Emotion Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle Perspective: Casting light on sleep deficiency Increasing trends of sleep complaints in the city of Sao Paulo Disparities in sleep characteristics by race/ethnicity in a population-based sample: Chicago Area Sleep Study Centers for Disease Control and Prevention - Unhealthy sleep-related behaviors–12 States Centers for Disease Control and Prevention 60 (2011) Sleep patterns in Amazon rubber tappers with and without electric light at home Access to Electric Light Is Associated with Shorter Sleep Duration in a Traditionally Hunter-Gatherer Community Adolescents living in homes without electric lighting have earlier sleep times and timing and their associations with age in a community without electricity in haiti Natural Sleep and Its Seasonal Variations in Three Pre-industrial Societies Cohort profile: the Baependi Heart Study - a family-based highly admixed cohort study in a rural Brazilian town Heritability of physical activity traits in Brazilian families: the Baependi Heart Study and age-at-onset of regular cigarette use in Brazilian families: the Baependi Heart Study Glycemic control and arterial stiffness in a Brazilian rural population: Baependi Heart Study Heritability of Obstructive Sleep Apnea in a rural population Distribution and heritability of diurnal preference (chronotype) in a rural Brazilian family-based cohort The Pittsburgh Sleep Quality Index: A New Instrument for Psychiatric Practice and Research A new method for measuring daytime sleepiness: the Epworth sleepiness scale The 3111 Clock gene polymorphism is not associated with sleep and circadian rhythmicity in phenotypically characterized human subjects Portuguese-language version of the Epworth sleepiness scale: validation for use in Brazil Relationship between self-reported sleep quality and metabolic syndrome in general population Poor sleep quality associated with high risk of hypertension and elevated blood pressure in China: results from a large population-based study Cross-sectional and Longitudinal Associations Between Objectively Measured Sleep Duration and Body Mass Index: The CARDIA Sleep Study and Excessive Daytime Sleepiness in Korean Adults A cross-national study of sleep problems in European older adults Sleep Problems: An Emerging Global Epidemic Findings From the INDEPTH WHO-SAGE Study Among More Than 40,000 Older Adults From 8 Countries Across Africa and Asia Insomnia and sleep apnea in midlife women: prevalence and consequences to health and functioning Sex differences in insomnia: a meta-analysis Test-retest reliability and validity of the Pittsburgh Sleep Quality Index in primary insomnia Sleep Duration and Body Mass Index in a Rural Population Obstructive Sleep Apnea Syndrome in the Sao Paulo Epidemiologic Sleep Study Validation of the Brazilian Portuguese version of the Pittsburgh Sleep Quality Index A Self-Assessment questionnaire to determine morningngess-eveningness in human circadian rhythms Download references We are very thankful to the population of Baependi for their participation in the Baependi Heart Study This study was supported by awards from CNPq to FB and by the Global Innovation Initiative to MvS (jointly funded by the British Council and the UK Department of Business and Skills) and by grants from Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP and Hospital Samaritano Society [Grant 25000.180.664/2011-35] through the Ministry of Health to Support Program Institutional Development of the Unified Health System (SUS-PROADI) Heart Institute (InCor) do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo Download citation + Francisca was born in São João del Rei, Brazil. As a child she entrusted herself to the care of the Blessed Virgin Mary. + A lay woman through her life, she lived as a modern-day anchoress in Baependi, Brazil, devoting her life to prayer and to the construction of a church dedicated to Mary. + Beloved by those who knew her for her wisdom and holiness, she died on June 14, 1895, and was buried in the church she helped to build. Blessed Francisca was beatified in 2013. “Here is a wise virgin, from among the number of the prudent, who went forth with lighted lamp to meet Christ.”—Entrance Antiphon for the Mass in honor of Virgins On this day, we also remember the Prophet Elisha. The disciple and protégé of the Prophet Elijah, Elisha took up the mantle of Elijah and he became the great prophet of the people of Israel. The stories of Elisha are recounted in the Books of Kings. Hear us, God our Savior, that, as we rejoice in commemorating the Virgin blessed Francisca, we may be instructed by her loving devotion. Through our Lord Jesus Christ, your Son, who lives and reigns with you in the unity of the Holy Spirit, one God, for ever and ever. Amen. (from The Roman Missal: Common of Virgins) Saint profiles prepared by Brother Silas Henderson, S.D.S. Our ancestors typically rose with the sun and went to sleep when it set, but modern life and artificial lighting has pushed this routine out of sync. However, researchers have discovered a rural community in Brazil that still follows the natural sleep cycles of the past  - despite having access to the same technology as its urban neighbours. And they now plan to study this group to learn more about how our move away from the natural rhythm could be damaging our health.  The community was discovered in the small town of Baependi in south-eastern Brazil in the state of Minais Gerais.  Researchers from the University of Surrey and the University of São Paulo studied the population and asked them questions about their sleep habits and patterns.  'In big cities, the availability of cheap electricity has brought us both artificial lighting and a multitude of other electronic devices that compete with us going to sleep at night,' said lead author Dr Malcolm von Schantz from the University of Surrey. 'As a result, most of us go to bed much later than our ancestors did, and, many of us are sleeping less.  'Even though the people in Baependi have access to electricity and television, their daily rhythms are much closer to those of previous generations.  'Studying this population is like being able to look back at past generations through a pair of binoculars and provide an insight into the benefit this natural pattern may be having on their health.' Historian Roger Ekirch of Virginia Tech recently revealed an 'overwhelming amount of historical evidence' that suggested we used to sleep in stages. He found more than 500 references about ancestors sleeping in two shorter periods throughout the night. The total sleep would occur in a 12-hour period that began with up to four hours sleep, an 'awake period' of four hours and then ended with a second four-hour sleep. These days it is widely accepted human sleep patterns are governed by the 'circadian rhythm'.  This is the 24-hour cycle of being awake and then, when it becomes dark, resting. 'However, built into this 24-hour pattern is a series of shorter cycles of about 90 minutes - called the "ultradian rhythm",' added Dr Nerina Ramlakhan, author of Tired But Wired: How To Overcome Your Sleep Problems. This explains smaller peaks and troughs of energy throughout the day. Dr Ramlakhan believes this ultradian rhythm is a throwback to our hunter-gatherer years. And while we tend to pay much more attention to the 24-hour cycle than the 90-minute one, Dr Ramlakhan believes the body works best when we move with these natural ultradian rhythms, building in pauses, stopping and resting, so continually renewing our energy.  In particular, the residents were asked when they would prefer to wake up and go to bed if they were completely free to plan their day. The average answers from town residents were 07.15 and 22.20, whereas people in the surrounding countryside preferred to rise at 06.30am and go to bed at 21.20.  The researchers believe the difference is due to town residents following much less of a natural sleep/wake cycle because of the influence of artificial lighting. 'When we asked the same question in London, the average answers were 08.30am and 23.15pm,' continued Dr von Schantz. The paper explained that the people of Baependi, especially those in the countryside, maintain a much stronger link with the so-called solar rhythm.  This is because they predominantly work outdoors and therefore have similar patterns as our pre-industrial ancestors.  Solar time uses the mid-points of the light and dark 'periods' - notably midnight and noon - as timing references.  In circadian rhythms, sunrise start this clock on its 24-hour run, but this continues regardless of a shift in when the sun sets meaning the mid-points vary. 'Midnight really represents the middle of the dark phase, and yet many of us in the industrialised world are not even in bed by then,' continued Dr von Schantz.  'Our colleagues at the University of São Paulo have studied this population, so there is a lot of data emerging about the health outcomes of the same population.  'We are optimistic that this project will teach us to what extent cardiovascular health, obesity, diabetes, and mental health problems may be associated with our move away from the natural day/night cycle, and the associated sleep loss.' Natural sleep cycles discovered in small Brazilian townCommenting on this article has endedNewest{{#isModerationStatus}}{{moderationStatus}}