Robust stability of melatonin circadian phase, sleep metrics, and chronotype across months in young adults living in real‐world settings

Feb 1, 2021Journal of pineal research

Consistent Melatonin Timing, Sleep Patterns, and Daily Rhythms Over Months in Young Adults Living Normally

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Abstract

Circadian timing was stable across ~100 days, with an intraclass correlation coefficient of 0.85 for melatonin onset.

Melatonin timing showed minimal change, with an average shift of only 21 minutes from the first month to the second and 5 minutes from the second to the third month.
Sleep behaviors exhibited high stability, with intraclass correlation coefficients ranging from 0.65 to 0.85.
Average melatonin timing was significantly associated with average chronotype, indicated by a correlation coefficient of r = 0.53.
Chronotype stability was also substantial over the study period, with an intraclass correlation coefficient of 0.61.

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Appropriate synchronization of the timing of behaviors with the circadian clock and adequate sleep are both important for almost every physiological process. The timing of the circadian clock relative to social (ie, local) clock time and the timing of sleep can vary greatly among individuals. Whether the timing of these processes is stable within an individual is not well-understood. We examined the stability of circadian-controlled melatonin timing, sleep timing, and their interaction across ~ 100 days in 15 students at a single university. At three time points ~ 35-days apart, circadian timing was determined from the dim-light melatonin onset (DLMO). Sleep behaviors (timing and duration) and chronotype (ie, mid-sleep time on free days corrected for sleep loss on school/work days) were determined via actigraphy and analyzed in ~ 1-month bins. Melatonin timing was stable, with an almost perfect relationship strength as determined via intraclass correlation coefficients ([ICC]=0.85); average DLMO timing across all participants only changed from the first month by 21 minutes in month 2 and 5 minutes in month 3. Sleep behaviors also demonstrated high stability, with ICC relationship strengths ranging from substantial to almost perfect (ICCs = 0.65-0.85). Average DLMO was significantly associated with average chronotype (r = 0.53, P <.01), with chronotype displaying substantial stability across months (ICC = 0.61). These findings of a robust stability in melatonin timing and sleep behaviors in young adults living in real-world settings holds promise for a better understanding of the reliability of previous cross-sectional reports and for the future individualized strategies to combat circadian-associated disease and impaired safety (ie, "chronomedicine"). 2

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Robust stability of melatonin circadian phase, sleep metrics, and chronotype across months in young adults living in real‐world settings

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