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Published on: April 7, 2020
The Circadian Response to Evening Light Spectra in Early Childhood: Preliminary Insights
Lauren E Hartstein1,2, Kenneth P Wright1, Cecilia Diniz Behn3,4
1Department of Integrative Physiology, University of Colorado Boulder, Boulder, Colorado.
Insights
Preschoolers
Area of Science:
- Chronobiology and developmental science.
- Pediatric sleep research.
- Environmental light exposure effects.
Background:
- Circadian system sensitivity to light is well-documented in adults, but less so in young children.
- Limited data exists on how light characteristics impact the circadian rhythm in early childhood.
- Understanding these effects is crucial for child development and health.
Purpose of the Study:
- To investigate the impact of different light color temperatures on the circadian response in preschool-aged children.
- To compare melatonin suppression and circadian phase shift following evening light exposure at low vs. high correlated color temperatures (CCT).
- To assess the sensitivity of the early childhood circadian system to light spectrum.
Main Methods:
- A crossover, within-subjects design was used with 10 healthy preschool-aged children (3.0-5.9 years).
- Participants underwent two 10-day protocols, each involving 7 days of stable sleep schedule followed by a 3-day in-home dim-light circadian assessment.
- Evening light exposure (1-hour, 20 lux) at either 2700K (low CCT) or 5000K (high CCT) was administered, with dim-light melatonin onset (DLMO) and salivary melatonin measured.
Main Results:
- Higher melatonin suppression was observed during high CCT (5000K) light exposure (56.3%) compared to low CCT (2700K) light (23.9%).
- Both light conditions induced significant delays in circadian timing.
- A small difference in phase delay was noted between the high CCT (35.3 min) and low CCT (26.7 min) conditions.
Conclusions:
- The circadian clock in preschool-aged children demonstrates high responsiveness to evening light exposure.
- Preliminary evidence suggests sensitivity to light spectrum, with higher CCT inducing greater melatonin suppression.
- Findings contribute to understanding light's role in early childhood circadian regulation.
Abstract:
Although the sensitivity of the circadian system to the characteristics of light (e.g., biological timing, intensity, duration, spectrum) has been well studied in adults, data in early childhood remain limited. Utilizing a crossover, within-subjects design, we examined differences in the circadian response to evening light exposure at two different correlated color temperatures (CCT) in preschool-aged children. Healthy, good sleeping children (n = 10, 3.0-5.9 years) completed two 10-day protocols. In each protocol, after maintaining a stable sleep schedule for 7 days, a 3-day in-home dim-light circadian assessment was performed. On the first and third evenings of the in-home protocol, dim-light melatonin onset (DLMO) was assessed. On the second evening, children received a 1-h light exposure of 20 lux from either 2700 K (low CCT) or 5000 K (high CCT) (~9 and ~16 melanopic equivalent daylight illuminance (mEDI lux), respectively) centered around their habitual bedtime. Children received the remaining light condition during their second protocol, with the order counterbalanced across participants. Salivary melatonin was collected to compute melatonin suppression and circadian phase shift resulting from each experimental light condition. Melatonin suppression across the 1-h light stimulus was significantly greater during exposure to the high CCT light (M = 56.3%, SD = 19.25%) than during the low CCT light (M = 23.90%, SD = 41.06%). Both light conditions resulted in marked delays of circadian timing, but only a small difference (d = -0.25) was observed in the delay between the 5000 K (M = 35.3 min, SD = 34.3 min) and 2700 K (M = 26.7 min, SD = 15.9 min) conditions. Together, these findings add to a growing literature demonstrating high responsivity of the circadian clock to evening light exposure in early childhood and provide preliminary evidence of melatonin suppression sensitivity to differences in light spectrum in preschool-aged children.
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