Peer-reviewed article
Variable Morning Melatonin Profiles Limit Determination of Dim-Light Melatonin Offset in Preschool-Aged Children.
Hartstein LE, Stowe SR, Wright KP, Diniz Behn C, LeBourgeois MK ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001This study examined circadian rhythm markers in 20 preschool-aged children by measuring melatonin levels in saliva samples collected throughout the day. The researchers found that evening melatonin onset could be reliably measured across all children, but morning melatonin levels were highly variable and irregular, making it difficult to determine the melatonin offset marker in most participants. The findings suggest that circadian assessment methods developed for adults may not work reliably in young children due to differences in melatonin patterns.
Key points
- Evening dim-light melatonin onset (DLMO) was successfully measured in all 20 children, ranging from 17:22 to 20:40, and correlated with bedtime and sleep timing
- Morning melatonin patterns were highly variable, allowing determination of dim-light melatonin offset (DLMOff) in only 8 of 20 children
- In the 8 children where DLMOff could be calculated, it showed strong associations with chronotype, sleep offset, and midsleep timing
- 45% of children had melatonin levels remaining at or above the 4 pg/ml threshold at their habitual wake time, suggesting melatonin offset often occurs after waking in young children
- The study indicates that morning melatonin profiles are fundamentally different in preschoolers compared to adults, limiting the use of standard circadian assessment protocols
Limitations
This is a small study of 20 healthy preschoolers with no comparison group, so findings may not generalize to all young children or those with sleep disorders or circadian disorders. The study does not evaluate an intervention to improve child health or well-being, only characterizes a biological marker.
Abstract
Circadian rhythms have been shown to regulate sleep-wake timing across the lifespan, yet many questions remain about early childhood circadian physiology. Understanding dim-light melatonin onset (DLMO) and offset (DLMOff), established markers of circadian phase, is essential for characterizing circadian rhythms in early childhood. We examined the distribution of salivary DLMO and DLMOff and their relationship with actigraphic sleep timing across 20 healthy preschoolers (M = 4.31 ± 0.34 years, 45% female). After maintaining a consistent sleep schedule for 7 days, children completed an in-home circadian assessment. Children were awoken 1.5 h before habitual wake time, and saliva samples were collected in 20- to 30-min intervals throughout the morning to determine DLMOff, then in the evening until 50 min past habitual bedtime to assess DLMO. A 4-pg/ml threshold was used to calculate each phase marker. DLMO ranged from 17:22 to 20:40 (M = 18:55 ± 0:54) and was positively associated with bedtime, sleep onset, and midsleep. In contrast, morning melatonin levels were highly variable, allowing DLMOff calculation in only 8 participants. Within this small subsample, later DLMOff was associated with later chronotype (r = 0.81), sleep offset (r = 0.84), and midsleep (r = 0.80). Across the full sample, interpolated melatonin levels at habitual wake remained ≥ 4 pg/ml for 45% of children, a pattern broadly consistent with findings in adults, in which a majority of participants exhibit DLMOff after habitual wake time. These findings indicate that although evening melatonin profiles were consistently well-defined, permitting reliable calculations of DLMO across all participants, morning melatonin patterns were often irregular in young children. When able to be calculated, DLMOff showed strong associations with sleep timing, suggesting it could be a reliable marker of circadian phase. However, high variability and fluctuating morning melatonin patterns make DLMOff difficult to determine in many preschool-aged children.