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Human Circadian Phenotyping and Diurnal Performance Testing in the Real World
Published on: April 7, 2020
A late wake time phase delays the human dim light melatonin rhythm
Helen J Burgess1, Charmane I Eastman
1Biological Rhythms Research Laboratory, Department of Behavioral Sciences, Rush University Medical Center, 1645 W. Jackson Blvd, Suite 425, Chicago, IL 60612, USA. helen_j_burgess@rush.edu
Neuroscience Letters
|November 29, 2005
Summary
Waking late significantly delays the human circadian clock
Area of Science:
- Chronobiology
- Sleep Science
- Human Physiology
Background:
- Short sleep durations are prevalent in modern society.
- Previous research linked late bedtimes to circadian rhythm delays.
- The impact of wake time on circadian rhythms requires further investigation.
Purpose of the Study:
- To investigate the effect of early versus late wake times on the human dim light melatonin rhythm.
- To determine if wake time influences circadian clock timing with a fixed bedtime.
Main Methods:
- Fourteen healthy subjects participated in a counterbalanced study.
- Participants experienced two weeks of short (6h) and two weeks of long (9h) nights.
- Wake times were fixed relative to habitual schedules, with a 3-hour difference between conditions.
Main Results:
- A late wake time resulted in a significant delay of dim light melatonin onset (2.4h) and offset (2.6h).
- These delays were observed compared to an early wake time condition.
- Statistical significance was high (p < 0.001) for both onset and offset delays.
Conclusions:
- Wake time, potentially through morning light exposure, substantially influences human circadian clock timing.
- Waking early leads to a phase advance of the circadian clock.
- Waking late results in a phase delay of the circadian clock.
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