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Wang W, Yuan RK, Mitchell JF, Zitting KM, St Hilaire MA, Wyatt JK, Scheer FAJL, Wright KP, Brown EN, Ronda JM, Klerman EB, Duffy JF, Dijk DJ, Czeisler CA. Desynchronizing the sleep---wake cycle from circadian timing to assess their separate contributions to physiology and behaviour and to estimate intrinsic circadian period. Nat Protoc 2023; 18:579-603. [PMID: 36376588 DOI: 10.1038/s41596-022-00746-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Accepted: 06/24/2022] [Indexed: 11/16/2022]
Abstract
Circadian clocks drive cyclic variations in many aspects of physiology, but some daily variations are evoked by periodic changes in the environment or sleep-wake state and associated behaviors, such as changes in posture, light levels, fasting or eating, rest or activity and social interactions; thus, it is often important to quantify the relative contributions of these factors. Yet, circadian rhythms and these evoked effects cannot be separated under typical 24-h day conditions, because circadian phase and the length of time awake or asleep co-vary. Nathaniel Kleitman's forced desynchrony (FD) protocol was designed to assess endogenous circadian rhythmicity and to separate circadian from evoked components of daily rhythms in multiple parameters. Under FD protocol conditions, light intensity is kept low to minimize its impact on the circadian pacemaker, and participants have sleep-wake state and associated behaviors scheduled to an imposed non-24-h cycle. The period of this imposed cycle, Τ, is chosen so that the circadian pacemaker cannot entrain to it and therefore continues to oscillate at its intrinsic period (τ, ~24.15 h), ensuring circadian components are separated from evoked components of daily rhythms. Here we provide detailed instructions and troubleshooting techniques on how to design, implement and analyze the data from an FD protocol. We provide two procedures: one with general guidance for designing an FD study and another with more precise instructions for replicating one of our previous FD studies. We discuss estimating circadian parameters and quantifying the separate contributions of circadian rhythmicity and the sleep-wake cycle, including statistical analysis procedures and an R package for conducting the non-orthogonal spectral analysis method that enables an accurate estimation of period, amplitude and phase.
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Affiliation(s)
- Wei Wang
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA.
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA.
| | - Robin K Yuan
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA
| | - Jude F Mitchell
- Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA
| | - Kirsi-Marja Zitting
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA
| | - Melissa A St Hilaire
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA
| | - James K Wyatt
- Department of Psychiatry and Behavioral Sciences, Rush University Medical Center, Chicago, IL, USA
| | - Frank A J L Scheer
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA
- Broad Institute, Cambridge, MA, USA
| | - Kenneth P Wright
- Sleep and Chronobiology Laboratory, Department of Integrative Physiology, University of Colorado Boulder, Boulder, CO, USA
| | - Emery N Brown
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Boston, MA, USA
- Department of Brain and Cognitive Science, Massachusetts Institute of Technology, Cambridge, MA, USA
- Institute for Medical Engineering and Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
- Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA, USA
- Institute for Data Systems and Society, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Joseph M Ronda
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA
| | - Elizabeth B Klerman
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA
- Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA, USA
- Department of Neurology, Massachusetts General Hospital, Boston, MA, USA
| | - Jeanne F Duffy
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA
| | - Derk-Jan Dijk
- Surrey Sleep Research Centre, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
- UK Dementia Research Institute Care Research and Technology Centre, Imperial College London and the University of Surrey, Guildford, UK
| | - Charles A Czeisler
- Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA, USA
- Division of Sleep Medicine and Department of Medicine, Harvard Medical School, Boston, MA, USA
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Lok R, Woelders T, van Koningsveld MJ, Oberman K, Fuhler SG, Beersma DGM, Hut RA. Bright Light Increases Alertness and Not Cortisol in Healthy Men: A Forced Desynchrony Study Under Dim and Bright Light (I). J Biol Rhythms 2022; 37:403-416. [PMID: 35686534 PMCID: PMC9326799 DOI: 10.1177/07487304221096945] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Light-induced improvements in alertness are more prominent during nighttime than during the day, suggesting that alerting effects of light may depend on internal clock time or wake duration. Relative contributions of both factors can be quantified using a forced desynchrony (FD) designs. FD designs have only been conducted under dim light conditions (<10 lux) since light above this amount can induce non-uniform phase progression of the circadian pacemaker (also called relative coordination). This complicates the mathematical separation of circadian clock phase from homeostatic sleep pressure effects. Here we investigate alerting effects of light in a novel 4 × 18 h FD protocol (5 h sleep, 13 h wake) under dim (6 lux) and bright light (1300 lux) conditions. Hourly saliva samples (melatonin and cortisol assessment) and 2-hourly test sessions were used to assess effects of bright light on subjective and objective alertness (electroencephalography and performance). Results reveal (1) stable free-running cortisol rhythms with uniform phase progression under both light conditions, suggesting that FD designs can be conducted under bright light conditions (1300 lux), (2) subjective alerting effects of light depend on elapsed time awake but not circadian clock phase, while (3) light consistently improves objective alertness independent of time awake or circadian clock phase. Reconstructing the daily time course by combining circadian clock phase and wake duration effects indicates that performance is improved during daytime, while subjective alertness remains unchanged. This suggests that high-intensity indoor lighting during the regular day might be beneficial for mental performance, even though this may not be perceived as such.
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Affiliation(s)
- R. Lok
- Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, the Netherlands
- Current address: Department of Psychiatry and Behavioral Sciences, Stanford University, Palo Alto, California, USA
- University of Groningen, Leeuwarden, the Netherlands
| | - T. Woelders
- Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, the Netherlands
| | - M. J. van Koningsveld
- Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, the Netherlands
| | - K. Oberman
- Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, the Netherlands
| | - S. G. Fuhler
- Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, the Netherlands
| | - D. G. M. Beersma
- Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, the Netherlands
| | - R. A. Hut
- Chronobiology Unit, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen, the Netherlands
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Sabzevari Rad R, Mahmoodzadeh Hosseini H, Shirvani H. Circadian rhythm effect on military physical fitness and field training: a narrative review. SPORT SCIENCES FOR HEALTH 2020. [DOI: 10.1007/s11332-020-00692-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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4
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Koritala BSC, Çakmaklı S. The human circadian clock from health to economics. Psych J 2018; 7:176-196. [DOI: 10.1002/pchj.252] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 09/13/2018] [Accepted: 09/19/2018] [Indexed: 12/18/2022]
Affiliation(s)
- Bala S. C. Koritala
- Department of Biology; Rutgers, The State University of New Jersey; Camden New Jersey USA
- Center for Computational and Integrative Biology; Rutgers, The State University of New Jersey; Camden New Jersey USA
| | - Selim Çakmaklı
- Department of Economics; Rutgers, The State University of New Jersey; Camden New Jersey USA
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5
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Yamanaka Y, Hashimoto S, Masubuchi S, Natsubori A, Nishide SY, Honma S, Honma KI. Differential regulation of circadian melatonin rhythm and sleep-wake cycle by bright lights and nonphotic time cues in humans. Am J Physiol Regul Integr Comp Physiol 2014; 307:R546-57. [PMID: 24944250 DOI: 10.1152/ajpregu.00087.2014] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Our previous study demonstrated that physical exercise under dim lights (<10 lux) accelerated reentrainment of the sleep-wake cycle but not the circadian melatonin rhythm to an 8-h phase-advanced sleep schedule, indicating differential effects of physical exercise on the human circadian system. The present study examined the effects of bright light (>5,000 lux) on exercise-induced acceleration of reentrainment because timed bright lights are known to reset the circadian pacemaker. Fifteen male subjects spent 12 days in temporal isolation. The sleep schedule was advanced from habitual sleep times by 8 h for 4 days, which was followed by a free-run session. In the shift session, bright lights were given during the waking time. Subjects in the exercise group performed 2-h bicycle running twice a day. Subjects in the control kept quiet. As a result, the sleep-wake cycle was fully entrained by the shift schedule in both groups. Bright light may strengthen the resetting potency of the shift schedule. By contrast, the circadian melatonin rhythm was phase-advanced by 6.9 h on average in the exercise group but only by 2.0 h in the control. Thus physical exercise prevented otherwise unavoidable internal desynchronization. Polysomnographical analyses revealed that deterioration of sleep quality by shift schedule was protected by physical exercise under bright lights. These findings indicate differential regulation of sleep-wake cycle and circadian melatonin rhythm by physical exercise in humans. The melatonin rhythm is regulated primarily by bright lights, whereas the sleep-wake cycle is by nonphotic time cues, such as physical exercise and shift schedule.
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Affiliation(s)
| | - Satoko Hashimoto
- Research Center for Cooperative Projects, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| | - Satoru Masubuchi
- Research Center for Cooperative Projects, Hokkaido University Graduate School of Medicine, Sapporo, Japan
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Mizuno K. Human circadian rhythms and exercise: Significance and application in real-life situations. THE JOURNAL OF PHYSICAL FITNESS AND SPORTS MEDICINE 2014. [DOI: 10.7600/jpfsm.3.307] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Effects of exercise on circadian rhythms and mobility in aging Drosophila melanogaster. Exp Gerontol 2013; 48:1260-5. [PMID: 23916842 DOI: 10.1016/j.exger.2013.07.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Revised: 07/14/2013] [Accepted: 07/25/2013] [Indexed: 11/20/2022]
Abstract
Daily life functions such as sleep and feeding oscillate with circa 24 h period due to endogenous circadian rhythms generated by circadian clocks. Genetic or environmental disruption of circadian rhythms is associated with various aging-related phenotypes. Circadian rhythms decay during normal aging, and there is a need to explore strategies that could avert age-related changes in the circadian system. Exercise was reported to delay aging in mammals. Here, we investigated whether daily exercise via stimulation of upward climbing movement could improve circadian rest/activity rhythms in aging Drosophila melanogaster. We found that repeated exercise regimen did not strengthen circadian locomotor activity rhythms in aging flies and had no effect on their lifespan. We also tested the effects of exercise on mobility and determined that regular exercise lowered age-specific climbing ability in both wild type and clock mutant flies. Interestingly, the climbing ability was most significantly reduced in flies carrying a null mutation in the core clock gene period, while rescue of this gene significantly improved climbing to wild type levels. Our work highlights the importance of period in sustaining endurance in aging flies exposed to physical challenge.
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Kalak N, Gerber M, Kirov R, Mikoteit T, Yordanova J, Pühse U, Holsboer-Trachsler E, Brand S. Daily morning running for 3 weeks improved sleep and psychological functioning in healthy adolescents compared with controls. J Adolesc Health 2012; 51:615-22. [PMID: 23174473 DOI: 10.1016/j.jadohealth.2012.02.020] [Citation(s) in RCA: 131] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2011] [Revised: 02/10/2012] [Accepted: 02/28/2012] [Indexed: 10/28/2022]
Abstract
PURPOSE To compare sleep electroencephalographic patterns and psychological functioning of healthy adolescents running regularly in the mornings with those of control subjects. Although several studies have shown that regular moderate-to-vigorous exercise is related to favorable sleep and psychological functioning in adolescents, research on the effectiveness of short interventions is more limited. METHODS Fifty-one adolescents (mean age = 18.30 years; 27 female [53%]) took part in the study; they were randomly assigned either to a running or to a control group. The running group went running every morning for 30 minutes at moderate intensity during weekdays for 3 consecutive weeks. Sleep electroencephalographic patterns and psychological functioning were assessed in both groups before and after the 3-week period. All participants also kept a sleep log for 3 weeks. RESULTS Objective sleep improved (slow-wave sleep increased; sleep onset latency decreased) in the running group compared with the control group. Subjective sleep quality, mood, and concentration during the day improved, whereas sleepiness during the day decreased. CONCLUSIONS Thirty minutes of running in the morning during weekdays for 3 consecutive weeks impacted positively on sleep and psychological functioning in healthy adolescents compared with control subjects. Running is inexpensive and easy to implement during school schedules, and as both objective and subjective improvements were observed within 3 weeks, regular physical exercise should be promoted.
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Affiliation(s)
- Nadeem Kalak
- Center for Affective, Stress and Sleep Disorders, Psychiatric Hospital of the University of Basel, Basel, Switzerland
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Kantermann T, Forstner S, Halle M, Schlangen L, Roenneberg T, Schmidt-Trucksäss A. The stimulating effect of bright light on physical performance depends on internal time. PLoS One 2012; 7:e40655. [PMID: 22808224 PMCID: PMC3394763 DOI: 10.1371/journal.pone.0040655] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Accepted: 06/11/2012] [Indexed: 01/28/2023] Open
Abstract
The human circadian clock regulates the daily timing of sleep, alertness and performance and is synchronized to the 24-h day by the environmental light-dark cycle. Bright light exposure has been shown to positively affect sleepiness and alertness, yet little is known about its effects on physical performance, especially in relation to chronotype. We, therefore, exposed 43 male participants (mean age 24.5 yrs ± SD 2.3 yrs) in a randomized crossover study to 160 minutes of bright (BL: ≈ 4.420 lx) and dim light (DL: ≈ 230 lx). During the last 40 minutes of these exposures, participants performed a bicycle ergometer test. Time-of-day of the exercise sessions did not differ between the BL and DL condition. Chronotype (MSF(sc), mid-sleep time on free days corrected for oversleep due to sleep debt on workdays) was assessed by the Munich ChronoType Questionnaire (MCTQ). Total work was significantly higher in BL (median 548.4 kJ, min 411.82 kJ, max 875.20 kJ) than in DL (median 521.5 kJ, min 384.33 kJ, max 861.23 kJ) (p = 0.004) going along with increased exhaustion levels in BL (blood lactate (+12.7%, p = 0.009), heart rate (+1.8%, p = 0.031), and Borg scale ratings (+2.6%, p = 0.005)) in all participants. The differences between total work levels in BL and DL were significantly higher (p = 0.004) if participants were tested at a respectively later time point after their individual mid-sleep (chronotype). These novel results demonstrate, that timed BL exposure enhances physical performance with concomitant increase in individual strain, and is related not only to local (external) time, but also to an individual's internal time.
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Affiliation(s)
- Thomas Kantermann
- Centre for Behaviour and Neurosciences, University of Groningen, Groningen, The Netherlands
| | | | - Martin Halle
- Department for Prevention and Sports Medicine, Technical University Munich, Munich, Germany
| | | | - Till Roenneberg
- Institute for Medical Psychology, Ludwig-Maximilians-University Munich, Munich, Germany
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10
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Duffy JF, Cain SW, Chang AM, Phillips AJK, Münch MY, Gronfier C, Wyatt JK, Dijk DJ, Wright KP, Czeisler CA. Sex difference in the near-24-hour intrinsic period of the human circadian timing system. Proc Natl Acad Sci U S A 2011; 108 Suppl 3:15602-8. [PMID: 21536890 PMCID: PMC3176605 DOI: 10.1073/pnas.1010666108] [Citation(s) in RCA: 379] [Impact Index Per Article: 29.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The circadian rhythms of melatonin and body temperature are set to an earlier hour in women than in men, even when the women and men maintain nearly identical and consistent bedtimes and wake times. Moreover, women tend to wake up earlier than men and exhibit a greater preference for morning activities than men. Although the neurobiological mechanism underlying this sex difference in circadian alignment is unknown, multiple studies in nonhuman animals have demonstrated a sex difference in circadian period that could account for such a difference in circadian alignment between women and men. Whether a sex difference in intrinsic circadian period in humans underlies the difference in circadian alignment between men and women is unknown. We analyzed precise estimates of intrinsic circadian period collected from 157 individuals (52 women, 105 men; aged 18-74 y) studied in a month-long inpatient protocol designed to minimize confounding influences on circadian period estimation. Overall, the average intrinsic period of the melatonin and temperature rhythms in this population was very close to 24 h [24.15 ± 0.2 h (24 h 9 min ± 12 min)]. We further found that the intrinsic circadian period was significantly shorter in women [24.09 ± 0.2 h (24 h 5 min ± 12 min)] than in men [24.19 ± 0.2 h (24 h 11 min ± 12 min); P < 0.01] and that a significantly greater proportion of women have intrinsic circadian periods shorter than 24.0 h (35% vs. 14%; P < 0.01). The shorter average intrinsic circadian period observed in women may have implications for understanding sex differences in habitual sleep duration and insomnia prevalence.
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Affiliation(s)
- Jeanne F. Duffy
- Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Division of Sleep Medicine, Harvard Medical School, Boston, MA 02115
| | - Sean W. Cain
- Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Division of Sleep Medicine, Harvard Medical School, Boston, MA 02115
| | - Anne-Marie Chang
- Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Division of Sleep Medicine, Harvard Medical School, Boston, MA 02115
| | - Andrew J. K. Phillips
- Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Division of Sleep Medicine, Harvard Medical School, Boston, MA 02115
| | | | | | | | | | | | - Charles A. Czeisler
- Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Division of Sleep Medicine, Harvard Medical School, Boston, MA 02115
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Jensen MA, Hansen AM, Abrahamsson P, Nørgaard AW. Development and evaluation of a liquid chromatography tandem mass spectrometry method for simultaneous determination of salivary melatonin, cortisol and testosterone. J Chromatogr B Analyt Technol Biomed Life Sci 2011; 879:2527-32. [PMID: 21803007 DOI: 10.1016/j.jchromb.2011.07.005] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Revised: 06/14/2011] [Accepted: 07/07/2011] [Indexed: 01/30/2023]
Abstract
Circadian disruption can have several possible health consequences, but is not well studied. In order to measure circadian disruption, in relation to shift or night work, we developed a simple and sensitive method for the simultaneous determination of melatonin, cortisol and testosterone in human saliva. We used liquid-liquid extraction (LLE) followed by liquid chromatography coupled to electrospray tandem mass spectrometry (LC-ESI-MS/MS) recorded in positive ion mode. Saliva samples were collected by spitting directly into tubes and 250 μL were used for analysis. The limits of detection were 4.1 pmol/L, 0.27 nmol/L and 10.8 pmol/L for melatonin, cortisol, and testosterone, respectively. The developed method was sensitive enough to measure circadian rhythms of all 3 hormones in a pilot study among four healthy volunteers. It can therefor be used to study the impact of night work and working in artificial light on the workers circadian rhythms. To our knowledge this is the first LC-ESI-MS/MS method for simultaneous determination of salivary melatonin, cortisol and testosterone.
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Affiliation(s)
- Marie Aarrebo Jensen
- National Research Centre for the Working Environment, Lersø Parkallé 105, DK-2100 Copenhagen Ø, Denmark.
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12
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Impact of the human circadian system, exercise, and their interaction on cardiovascular function. Proc Natl Acad Sci U S A 2010; 107:20541-6. [PMID: 21059915 DOI: 10.1073/pnas.1006749107] [Citation(s) in RCA: 213] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The risk of adverse cardiovascular events peaks in the morning (≈9:00 AM) with a secondary peak in the evening (≈8:00 PM) and a trough at night. This pattern is generally believed to be caused by the day/night distribution of behavioral triggers, but it is unknown whether the endogenous circadian system contributes to these daily fluctuations. Thus, we tested the hypotheses that the circadian system modulates autonomic, hemodynamic, and hemostatic risk markers at rest, and that behavioral stressors have different effects when they occur at different internal circadian phases. Twelve healthy adults were each studied in a 240-h forced desynchrony protocol in dim light while standardized rest and exercise periods were uniformly distributed across the circadian cycle. At rest, there were large circadian variations in plasma cortisol (peak-to-trough ≈85% of mean, peaking at a circadian phase corresponding to ≈9:00 AM) and in circulating catecholamines (epinephrine, ≈70%; norepinephrine, ≈35%, peaking during the biological day). At ≈8:00 PM, there was a circadian peak in blood pressure and a trough in cardiac vagal modulation. Sympathetic variables were consistently lowest and vagal markers highest during the biological night. We detected no simple circadian effect on hemostasis, although platelet aggregability had two peaks: at ≈noon and ≈11:00 PM. There was circadian modulation of the cardiovascular reactivity to exercise, with greatest vagal withdrawal at ≈9:00 AM and peaks in catecholamine reactivity at ≈9:00 AM and ≈9:00 PM. Thus, the circadian system modulates numerous cardiovascular risk markers at rest as well as their reactivity to exercise, with resultant profiles that could potentially contribute to the day/night pattern of adverse cardiovascular events.
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Abstract
The circadian system in animals and humans, being near but not exactly 24-hours in cycle length, must be reset on a daily basis in order to remain in synchrony with external environmental time. This process of entrainment is achieved in most mammals through regular exposure to light and darkness. In this chapter, we review the results of studies conducted in our laboratory and others over the past 25 years in which the effects of light on the human circadian timing system were investigated. These studies have revealed, how the timing, intensity, duration, and wavelength of light affect the human biological clock. Our most recent studies also demonstrate that there is much yet to learn about the effects of light on the human circadian timing system.
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Affiliation(s)
- Jeanne F. Duffy
- Assistant Professor of Medicine, Division of Sleep Medicine, Brigham & Women’s Hospital and Harvard Medical School, Boston, Massachusetts
| | - Charles A. Czeisler
- Baldino Professor of Sleep Medicine and Director of the Division of Sleep Medicine, Harvard Medical School, Boston, Massachusetts
- Chief, Division of Sleep Medicine, Department of Medicine, Brigham and Women’s Hospital, Boston, Massachusetts
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