L5 onset as a proxy for circadian phase in infants

Jun 5, 2026Chronobiology international

Using the timing of the last daily meal to estimate infants' body clock phase

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Abstract

A positive correlation of 0.22 between mid-sleep point and L5 onset was observed in 81 six-month-old infants.

Mid-sleep point is commonly used to assess circadian phase but is less applicable in infants.
L5 onset is a derived measure that indicates the start of the least active 5-hour period based on rest-activity rhythms.
Significant associations were found between mid-sleep point and L5 onset both across different infants and within the same infant over time.
These results indicate that L5 onset could be a practical alternative for assessing circadian phase in young infants.

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Chronotype is commonly assessed using the mid-sleep point as an indicator of circadian phase. In infants, however, this assessment typically relies on actigraphy, and most available sleep-scoring algorithms have been developed and validated for adolescents and adults, limiting their applicability in early childhood. The aim of this study was to examine the relationship between the mid-sleep point and L5 onset, a nonparametric measure derived from rest-activity rhythms that reflects the start of the least active 5-h period. A total of 502 nights from 81 six-month-old infants were analyzed. Sleep onset and offset were determined by visual inspection of actograms, and the mid-sleep point was subsequently calculated. A positive correlation was observed between mid-sleep point and L5 onset ( = 0.22, < 0.001). Linear mixed-effects models indicated significant associations both between infants (β = 0.63, < 0.001) and within infants (β = 0.10, < 0.001). These findings suggest that L5 onset may serve as a practical proxy for circadian phase in 6-month-old infants, offering an alternative to sleep parameters derived from algorithms not specifically validated for this age group. r p p p

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L5 onset as a proxy for circadian phase in infants

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