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L5 onset as a proxy for circadian phase in infants
Rebeca Buest de Mesquita Silva1, Adrielle Holler Pykocz1, Hanna Victoria Leal1
1Physiology Department, Federal University of Paraná, Curitiba, Brazil.
Chronobiology International
|June 5, 2026
Summary
L5 onset, a measure of infant rest-activity, correlates with mid-sleep points. This suggests L5 onset can be a practical proxy for circadian phase in 6-month-old infants when standard algorithms are unavailable.
Area of Science:
- Pediatrics
- Chronobiology
- Sleep Science
Background:
- Chronotype assessment commonly uses mid-sleep points to indicate circadian phase.
- Existing sleep-scoring algorithms are primarily validated for adults and adolescents, not infants.
- Infant chronotype assessment often relies on actigraphy, necessitating age-appropriate methods.
Purpose of the Study:
- To investigate the relationship between mid-sleep point and L5 onset in 6-month-old infants.
- To determine if L5 onset can serve as a reliable proxy for circadian phase in infants.
- To address limitations of current sleep-scoring algorithms in early childhood.
Main Methods:
- Analysis of 502 nights of sleep data from 81 six-month-old infants.
- Visual inspection of actograms to determine sleep onset and offset.
- Calculation of mid-sleep point and L5 onset (start of the least active 5-hour period).
Main Results:
- A significant positive correlation was found between mid-sleep point and L5 onset (r=0.22, p<0.001).
- Linear mixed-effects models showed significant associations both between infants (β=0.63, p<0.001) and within infants (β=0.10, p<0.001).
Conclusions:
- L5 onset is a practical and suitable proxy for circadian phase in 6-month-old infants.
- This finding provides an alternative to sleep parameters from algorithms not validated for infant populations.
- Supports the use of nonparametric measures for infant circadian rhythm assessment.
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