Weekly and seasonal variation in the circadian melatonin rhythm in humans: Entrained to local clock time, social time, light exposure or sun time?

A recent elegant study published in this journal (Zerbini, Winnebeck & Merrow, J Pineal Res, e12723, 2021) reported data on weekly and seasonal changes in circadian timing, as assessed by the melatonin rhythm in dim light in a population that was exposed to a change from standard time to day lig...

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Bibliographic Details
Published in:Journal of pineal research 2021-08, Vol.71 (1), p.e12746-n/a
Main Authors: Skeldon, Anne C., Dijk, Derk‐Jan
Format: Article
Language:English
Subjects:
circadian phase
Circadian Rhythm
entrainment
Humans
Light
Melatonin
Seasons
sun time
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Summary:A recent elegant study published in this journal (Zerbini, Winnebeck & Merrow, J Pineal Res, e12723, 2021) reported data on weekly and seasonal changes in circadian timing, as assessed by the melatonin rhythm in dim light in a population that was exposed to a change from standard time to day light saving time. The authors highlight a one hour earlier timing of melatonin onset in summer compared with winter and a 20 minutes delay on work‐free days compared with work days. The variations in the timing of the melatonin rhythm are reported in standard time and the authors imply that the data are consistent with synchronization to midday and that “we know that humans entrain to sun time.” Here, we show that their extensive data are most parsimoniously explained by entrainment to local clock time and associated light exposure rather than “sun time,” indexed by either dawn or midday.
ISSN:0742-3098
1600-079X
DOI:10.1111/jpi.12746