Circadian rhythms of European and African-Americans after a large delay of sleep as in jet lag and night work

Eastman, Charmane I.; Tomaka, Victoria A.; Crowley, Stephanie J.

doi:10.1038/srep36716

Cited by 48 publications

(53 citation statements)

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“…An individual’s circadian period is important because it helps determine circadian phase and circadian phase angle (Duffy et al, 2001., Eastman et al, 2015; Eastman et al, 2016; Gronfier et al, 2007; Pittendrigh & Daan, 1976; Sharma & Chandrashekaran, 1998; Wright et al, 2005). Circadian period also determines the direction and magnitude of the phase shift of the circadian clock after a large phase shift of the sleep schedule as in shift work and jet travel (Eastman et al, 2015; Eastman et al, 2016).…”

Section: Discussionmentioning

confidence: 99%

“…Details about the study protocols and the study populations are provided in the two primary publications (Eastman et al, 2015; Eastman et al, 2016). There were 36 participants in the first study (conducted between January 2013 and May 2014) (Eastman et al, 2015) and 45 participants in the second study (November 2014 to July 2016) (Eastman et al, 2016). Participants were run during all seasons except for summer.…”

Section: Methodsmentioning

confidence: 99%

“…These 2 × 10 days had identical protocols (Eastman et al, 2015; Eastman et al, 2016). The first 5 of these days were used to determine the free-running circadian period (tau).…”

Section: Methodsmentioning

confidence: 99%

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Circadian phase, circadian period and chronotype are reproducible over months

Kantermann

Eastman

2017

Chronobiology International

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The timing of the circadian clock, circadian period and chronotype varies among individuals. To date, not much is known about how these parameters vary over time in an individual. We performed an analysis of the following five common circadian clock and chronotype measures: 1) the dim light melatonin onset (DLMO, a measure of circadian phase), 2) phase angle of entrainment (the phase the circadian clock assumes within the 24-h day, measured here as the interval between DLMO and bedtime/dark onset), 3) free-running circadian period (tau) from an ultradian forced desynchrony protocol; tau influences circadian phase and phase angle of entrainment, 4) mid-sleep on work-free days (MSF from the Munich ChronoType Questionnaire; MCTQ), and 5) the score from the Morningness-Eveningness Questionnaire (MEQ). The first three are objective physiological measures, and the last two are measures of chronotype obtained from questionnaires. These data were collected from 18 individuals (10 men, 8 women, ages 21 to 44) who participated in two studies with identical protocols for the first 10 days. We show how much these circadian rhythm and chronotype measures changed from the first to the second study. The time between the two studies ranged from 9 months to almost 3 years, depending on the individual. Since the full experiment required living in the laboratory for 14 days, participants were either unemployed, had part-time jobs or were free-lance workers with flexible hours. Thus, they did not have many constraints on their sleep schedules before the studies. The DLMO was measured on the first night in the lab, after free-sleeping at home, and also after sleeping in the lab on fixed 8-h sleep schedules (loosely tailored to their sleep times before entering the laboratory) for four nights. Graphs with lines of unity (when the value from the first study is identical to the value from the second study) showed how much each variable changed from the first to the second study. The DLMO did not change more than 2 h from the first to the second study, except for two participants whose sleep schedules changed the most between studies, a change in sleep times of 3 h. Phase angle did not change more than 2 h regardless of changes in the sleep schedule. Circadian period did not change more than 0.2 h, except for one participant. MSF did not change more than 1 h, except for 2 participants. MEQ did not change more than 10 points and the categories (e.g. M-type) did not change. Pearson’s correlations for the DLMO between the first and second study increased after participants slept in the lab on their individually timed fixed 8-h sleep schedules for four nights. A longer time between the two studies did not increase the difference between any of the variables from the first to the second study. This analysis shows that the circadian clock and chronotype measures were fairly reproducible, even after many months between the two studies.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Circadian phase, circadian period and chronotype are reproducible over months

Kantermann

Eastman

2017

Chronobiology International

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“…The ultradian light-dark (LD) cycle is a forced desynchrony protocol; a 4-h day is beyond the limits of entrainment, and therefore the circadian clock free runs (Kripke et al, 2007; Burgess and Eastman, 2008; Burgess et al, 2008; Smith et al, 2009; Burgess et al, 2010; Eastman et al, 2012; Revell et al, 2012; Eastman et al, 2015; Eastman et al, 2016). Circadian period was computed from the DLMO phase shift from the baseline to final phase assessments during the room light session when bright light stimuli were absent.…”

Section: Methodsmentioning

confidence: 99%

Human Adolescent Phase Response Curves to Bright White Light

Crowley

Eastman

2017

J Biol Rhythms

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Older adolescents are particularly vulnerable to circadian misalignment and sleep restriction, primarily due to early school start times. Light can shift the circadian system and could help attenuate circadian misalignment; however, a phase response curve (PRC) to determine the optimal time for receiving light and avoiding light is not available for adolescents. We constructed light PRCs for late- to post-pubertal adolescents aged 14 to 17 years. Participants completed two counterbalanced 5-day laboratory sessions after 8 or 9 days of scheduled sleep at home. Each session included phase assessments to measure the dim light melatonin onset (DLMO) before and after 3 days of free-running through an ultradian light-dark (wake-sleep) cycle (2 h dim (~20 lux) light, 2 h dark). In one session, intermittent bright white light (~5000 lux; four 20-min exposures) alternated with 10 min dim room light once per day for 3 consecutive days. The time of light varied among participants to cover the 24-h day. For each individual, the phase shift to bright light was corrected for the free-run derived from the other laboratory session with no bright light. One PRC showed phase shifts in response to light start time relative to the DLMO, and another relative to home sleep. Phase delay shifts occurred around the hours corresponding to home bedtime. Phase advances occurred during the hours surrounding wake time and later in the afternoon. The transition from delays to advances occurred at the midpoint of home sleep. The adolescent PRCs presented here provide a valuable tool to time bright light in adolescents.

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“…Indeed, when choosing cutoffs from earlier studies to classify chronotypes as early (<3:00), intermediate (3:00-5:00) and late (>5:00) [2], we find 40% early, 44% intermediate and only 16% late chronotypes. Cut-offs are sensitive to the study population (e.g., race/ethnicity [48,49]) and other differences need to be examined, such as latitude and longitude [50], position within a time zone [17], and work schedules (day work vs. shift work) [51,52]. Thus, cut-offs should be interpreted with caution.…”

Section: Limitationsmentioning

confidence: 99%

0158 Chronotypes in the Us - Influence of Age and Sex

Fischer

Lombardi

Wellman-Marucci

et al. 2017

Sleep

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An individual's chronotype reflects how the circadian system embeds itself into the 24-h day with rhythms in physiology, cognition and behavior occurring accordingly earlier or later. In view of an increasing number of people working at unusual times and linked health and safety risks, the wide range in human chronotypes may provide opportunities to allow people to work (and sleep) at times that are in synch with their circadian physiology. We aimed at estimating the distribution of chronotypes in the US population by age and sex. Twelve years (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) of pooled diary data from the American Time Use Survey were used to calculate chronotype based on mid-point of sleep on weekends (MSF We , n = 53,689). We observed a near-normal distribution overall and within each age group. The distribution's mean value is systematically different with age, shifting later during adolescence, showing a peak in 'lateness' at~19 years, and shifting earlier thereafter. Men are typically later chronotypes than women before 40, but earlier types after 40. The greatest differences are observed between 15 and 25 for both sexes, equaling more than 50% of the total chronotype difference across all age groups. The variability in chronotype decreases with age, but is generally higher in males than females. This is the first study to estimate the distribution and prevalence of individual chronotypes in the US population based on a large-scale, nationally representative sample. Our finding that adolescents are on average the latest chronotypes supports delaying school start times to benefit their sleep and circadian alignment. The generally wide range in chronotypes may provide opportunities for tailored work schedules by matching external and internal time, potentially decreasing long-and shortterm health and safety risks.

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Circadian rhythms of European and African-Americans after a large delay of sleep as in jet lag and night work

Cited by 48 publications

References 50 publications

Circadian phase, circadian period and chronotype are reproducible over months

Circadian phase, circadian period and chronotype are reproducible over months

Human Adolescent Phase Response Curves to Bright White Light

0158 Chronotypes in the Us - Influence of Age and Sex

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