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Cited by 113Circadian rhythm and melatoninSleep and Work-Related FatigueSleep and related disorders

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Racial Differences in the Human Endogenous Circadian Period

Open access
Smith, Mark R., Burgess, Helen J., Fogg, Louis F., Eastman, Charmane I.·2009·PLoS ONE
DOI 10.1371/journal.pone.0006014PMC PMC2699031
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Abstract

The length of the endogenous period of the human circadian clock (tau) is slightly greater than 24 hours. There are individual differences in tau, which influence the phase angle of entrainment to the light/dark (LD) cycle, and in doing so contribute to morningness-eveningness. We have recently reported that tau measured in subjects living on an ultradian LD cycle averaged 24.2 hours, and is similar to tau measured using different experimental methods. Here we report racial differences in tau. Subjects lived on an ultradian LD cycle (1.5 hours sleep, 2.5 hours wake) for 3 days. Circadian phase assessments were conducted before and after the ultradian days to determine the change in circadian phase, which was attributed to tau. African American subjects had a significantly shorter tau than subjects of other races. We also tested for racial differences in our previous circadian phase advancing and phase delaying studies. In the phase advancing study, subjects underwent 4 days of a gradually advancing sleep schedule combined with a bright light pulse upon awakening each morning. In the phase delaying study, subjects underwent 4 days of a gradually delaying sleep schedule combined with evening light pulses before bedtime. African American subjects had larger phase advances and smaller phase delays, relative to Caucasian subjects. The racial differences in tau and circadian phase shifting have important implications for understanding normal phase differences between individuals, for developing solutions to the problems of jet lag and shift work, and for the diagnosis and treatment of circadian rhythm based sleep disorders such as advanced and delayed sleep phase disorder.

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Figure 1 Racial differences in the human endogenous circadian period. The human endogenous circadian period depends on race, season, and age. (a) Histogram of circadian period (tau) for subjects (n = 60) whose self-reported race was African American (black bars) or not African American (white bars). (b) Circadian period by self-reported race. (c) Circadian period by 2 month bins. In (b) and (c), horizontal lines depict the mean. (d) Circadian period by age. Black dots in (c) and (d) indicate African American subjects.
Figure 1 Racial differences in the human endogenous circadian period. The human endogenous circadian period depends on race, season, and age. (a) Histogram of circadian period (tau) for subjects (n = 60) whose self-reported race was African American (black bars) or not African American (white bars). (b) Circadian period by self-reported race. (c) Circadian period by 2 month bins. In (b) and (c), horizontal lines depict the mean. (d) Circadian period by age. Black dots in (c) and (d) indicate African American subjects.CC BY · PubMed Central
Figure 2 Racial differences in the magnitude of phase shifts to bright-light pulses and shifts of the sleep/dark schedule. Circadian phase advance (a) and phase delay (b) of the DLMO by self-reported race. By convention, phase advances are plotted as positive numbers and phase delays are plotted as negative numbers. Lines indicate the mean of each race.
Figure 2 Racial differences in the magnitude of phase shifts to bright-light pulses and shifts of the sleep/dark schedule. Circadian phase advance (a) and phase delay (b) of the DLMO by self-reported race. By convention, phase advances are plotted as positive numbers and phase delays are plotted as negative numbers. Lines indicate the mean of each race.CC BY · PubMed Central

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Research works printed but not linked: 1

  1. [14]Pittendrigh CS Daan S 1976 A functional analysis of circadian pacemakers in nocturnal rodents. IV. Entrainment: pacemaker as clock. Journal of Comparative Physiology 106 291 331

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Metadata

Authors
Smith, M. R., Burgess, H. J., Fogg, L. F., & Eastman, C. I.
Affiliations
Rush University Medical Center (US)
Corresponding author
Eastman, Charmane I.
ORCID
Venue
PLoS ONE
Publisher
Public Library of Science (PLoS)
Published
2009-06-30
Volume
4
Issue
6
Pages
e6014
ISSN
1932-6203 (ISSN-L)
DOI
10.1371/journal.pone.0006014
PMC
PMC2699031
OpenAlex
W2000253660
Cited by
113
References
37
Citations by year
2026: 5 · 2025: 3 · 2024: 5 · 2023: 6 · 2022: 9 · 2021: 8 · 2020: 7 · 2019: 9 · 2018: 7 · 2017: 10 · 2016: 4 · 2015: 13 · 2014: 6 · 2013: 4 · 2012: 8
FWCI
2.54
Type
journal article
Language
en
Open access
Licence
Locations
  • PLoS ONE (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Figshare (submittedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • National Institutes of Health
  • National Heart, Lung, and Blood Institute (R01HL086934)
  • National Institute of Nursing Research (R01NR007677)
Topics
  • Life Sciences › Neuroscience › Endocrine and Autonomic Systems › Circadian rhythm and melatonin
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and Work-Related Fatigue
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and related disorders
Keywords
circadian period, racial differences, African Americans, circadian phase, chronotype, phase shifting, light pulses, jet lag, shift work, circadian rhythm sleep disorders, delayed sleep phase syndrome
MeSH terms
Adult, Biological Clocks, Black or African American, Circadian Rhythm, Ethnicity, Female, Humans, Iris, Light, Male, Surveys and Questionnaires, Sleep, Sleep Wake Disorders, Time Factors, Wakefulness, Photoperiod

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