ring the bell for matins: circadian adaptation to split sleep by cloistered monks and nuns

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  • Ring the Bell for Matins: Circadian Adaptation to Split Sleep by CloisteredMonks and Nuns

    Isabelle Arnulf,1,2 Agns Brion,1 Michel Pottier,1 and Jean-Louis Golmard3

    1Sleep Disorders Unit, Piti-Salptrire Hospital, APHP, Paris, France, 2CRICMPierre and Marie Curie University, Inserm UMR_S975, CNRS UMR 722, Paris, France, 3Department of Biostatistics, Piti-Salptrire Hospital, ER4, Pierre and Marie Curie University,Paris, France

    Cloistered monks and nuns adhere to a 10-century-old strict schedule with a common zeitgeber of a night split by a2- to 3-h-long Office (Matins). The authors evaluated how the circadian core body temperature rhythm and sleepadapt in cloistered monks and nuns in two monasteries. Five monks and five nuns following the split-sleep nightschedule for 5 to 46 yrs without interruption and 10 controls underwent interviews, sleep scales, and physicalexamination and produced a week-long sleep diary and actigraphy, plus 48-h recordings of core body temperature.The circadian rhythm of temperature was described by partial Fourier time-series analysis (with 12- and 24-hharmonics). The temperature peak and trough values and clock times did not differ between groups. However, thetemperature rhythm was biphasic in monks and nuns, with an early decrease at 19:39 4:30 h (median 95%interval), plateau or rise of temperature at 22:35 00:23 h (while asleep) lasting 296 39 min, followed by a seconddecrease after the Matins Office, and a classical morning rise. Although they required alarm clocks to wake-up forMatins at midnight, the body temperature rise anticipated the nocturnal awakening by 85 15 min. Compared tothe controls, the monks and nuns had an earlier sleep onset (20:05 00:59 h vs. 00:00 00:54 h, median 95%confidence interval, p = .0001) and offset (06:27 0:22 h, vs. 07:37 0:33 h, p = .0001), as well as a shorter sleep time(6.5 0.6 vs. 7.6 0.7 h, p = .05). They reported difficulties with sleep latency, sleep duration, and daytime function,and more frequent hypnagogic hallucinations. In contrast to their daytime silence, they experienced conversations(and occasionally prayers) in dreams. The biphasic temperature profile in monks and nuns suggests the humanclock adapts to and even anticipates nocturnal awakenings. It resembles the biphasic sleep and rhythm of healthyvolunteers transferred to a short (10-h) photoperiod and provides a living glance into the sleep pattern of medievaltime. (Author correspondence: isabelle.arnulf@psl.aphp.fr)

    Keywords: Biphasic, Circadian, Clock, Core body temperature, Monastery, Monk, Sleep, Split sleep


    Catholic religious life has organized a circadian rhythmsince medieval times that is still maintained today withinmonasteries of cloistered persons (referred to here asmonks). Throughout days and nights, the monks pray,work, eat, and rest at the same time, with a common zeitge-ber (the tower clock bell). This rhythmpredictably changeson certain days (e.g., Friday, Sunday) and periods of theyear (e.g., winter fast, Christmas, Easter). Little is knownabout the habits and quality of sleep in the residents ofthese communities. The sleep of 10 nuns who had amodest habitual sleep restriction was monitored in asingle study by Hoch et al. (1987). They slept better, withshorter sleep latency, higher sleep efficiency, and morerapid eye movement (REM) sleep time, than controls.However, they had a single sleep period without any inter-

    ruption. In some strict orders, nighttime sleep is inter-rupted by long prayer Offices (called Matins or Vigils) thathave existed since the origin of monastic life. Contrary toshiftworkers and solitary sailors (e.g., kerstedt et al.,2010; Ferguson et al., 2008; Ohayon et al., 2010), monksfreely volunteer to follow this unusual rhythm duringtheir entire life without interruption during weekends orvacations. Hence, they constitute an exceptional model toobserve how the biological clock and the human adapt tosplit and curtailed sleep. We investigated sleep and bodytemperature circadian rhythm in a sample of 10 monks.


    The historical notes in the appendix of this article wereobtained from a nonexhaustive study of books relatedto sleep at circadian times in Catholic monasteries, with

    Address correspondence to Dr. Isabelle Arnulf, Unit des Pathologies du Sommeil, Hpital Piti-Salptrire, 4783 boulevard de lHpital,75651 Paris Cedex 13, France. Tel.: 00 33 1 42 16 77 01; Fax: 00 33 1 42 16 77 00; E-mail: isabelle.arnulf@psl.aphp.fr

    Submitted February 20, 2011, Returned for revision March 18, 2011, Accepted September 7, 2011

    Chronobiology International, 28(10): 930941, (2011)Copyright Informa Healthcare USA, Inc.ISSN 0742-0528 print/1525-6073 onlineDOI: 10.3109/07420528.2011.624436



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  • the help of university faculties and librarians of variousorders. We were able to speak with 17 monks from thestudied Order. A more complete prospective study ofsleep, circadian rhythms, and food intake was performedin a subset of 10 monks and 10 controls.

    SubjectsAfter having obtained agreement for the study from theethical committee (Ile de France 03), we submitted the pro-tocol to the Superior of the Order, who approved it. He rec-ommended that the Order and the locations of the studyremain anonymous, that the study include monks (as hehad indications that nuns had more difficulties thanmonks adapting to split nights), and that the study be per-formed outside the fasting (as members would be lesstired) and feast (such as Easter) times. He specified thatthe community was interested in any expert advice thatcould improve the adjustment of the monks to their night-time split-sleep schedule. The Prior and Prioress asked forfive volunteers of two monasteries (of 30 members in themonksmonastery and of 12members in the nunsmonas-tery). The criteria for inclusion were to be fully Frenchspeaking (as these monasteries contained members from15 different countries) and nonusers of medication thatcould interfere with the measure of circadian time orsleep. The controls were men and women from theoutside world, recruited among friends and family of theinvestigators, who agreed to take part as controls by altru-ism. They were matched for age ( 4 yr) and sex, and werestudied during the same month and at the same altitudeas were the monks. The protocol and analysis conformedto the ethics and methods required by the journal (Porta-luppi et al., 2010).

    Study Setting

    Life in the MonasteryThemonks followed a strictly identical rule in bothmonas-teries (Table 1). The organization of sleep time has beenunchanged since 1423. At the time of the study (July), themonks ate twomeals/d alone in their cell, including acom-plete lunch, a lightmeal beforeCompline, but nobreakfast.The daily diet contained no meat (a remnant of medievaltime when meat was expensive), but fish or eggs, two veg-etables (one starchy), soup, four fruits, butter (20 g),cheese, yoghurt, or jam, two cookies or little cakes,bread, milk, fruit juice, or wine; obviously most monksdid not eat all of this, but only what they needed.

    Circadian TimeElectrical clocks, set up on the country local time, wereused in the two monasteries. All monks woke-up usingan alarm clock. In addition, monks wore a wristwatchon special occasions (like our study), which they fre-quently checked during the medical interviews (dis-cussed later). The rest of the time, they easily regulatedtheir time by the tower clock bell. The Father in chargeof the young candidates to the monastic life indicated

    that candidates usually needed 6 mo to adjust to themonastic schedule. They would occasionally depend onherbal tea or hot wine with herbs, but not hypnotics,for sleeping. The books of the Order recommendedmonks promptly go to bed after Compline. If sleep wasdifficult to initiate, they were advised to turn theirthoughts toward the Christ in the main church, rep-resented by a permanent small vigil lamp.

    Life in SilenceBoth monasteries were built in a remote, elevated area,with forests and silence surrounding them. The monkslived together as a community of hermits, with a vow ofsilence and reduced contact with the outside world andother members of the community. Greetings werelimited to a silent head nodding when they crossed inthe cloister. They would write messages on small piecesof paper to make known their need(s). They lived alonein their own cell (a four-room house with a smallgarden surrounded by high walls). Their food was deliv-ered once daily in their cell by a brother via a hatch. Theyleft the hermitage cell daily to attend three prayer servicesin the monastery church. Additionally, once a week, thecommunity members took a long walk together for anafternoon in the countryside, during which they wereencouraged to speak. The monks frequently reportedthat living in loneliness and silence could make themover-sensitive to noise and the attitudes of othermembers, which could impact their sleep at night.

    MatinsA first bell rang a single beat at 23:45 h (for waking-up,getting dressed, and briefly praying in the cell), followedby a single beat at midnight (for coming to the church),and several beats at 00:15 h (the beginning of theMatins), with a monk designated to ring the bell bypulling on a long cord. The members came together insilence and joined the others in the dark. The monksprayed in silence for 3 min and then the Prior knockedon the wooden stall, which indicated the beginning ofMatins. If a monk was absent, the Sacristan went to seekhim in his cell and determine if he might be ill. The temp-erature of the church was 21C