Sensitivity of the circadian system to evening bright light in preschool-age children

Abstract

Although the light-induced melatonin suppression response is well characterized in adults, studies examining the dynamics of this effect in children are scarce. The purpose of this study was to quantify the magnitude of evening light-induced melatonin suppression in preschool-age children. Healthy children (n = 10; 7 females; 4.3 ± 1.1 years) participated in a 7-day protocol. On days 1-5, children followed a strict sleep schedule. On day 6, children entered a dim light environment (<15 lux) for 1-h before providing salivary samples every 20- to 30-min from the afternoon until 50-min after scheduled bedtime. On day 7, subjects remained in dim light conditions until 1-h before bedtime, at which time they were exposed to a bright light stimulus (~1000 lux) for 1-h and then re-entered dim light conditions. Saliva samples were obtained before, during, and after bright light exposure and were time anchored to samples taken the previous evening. We found robust melatonin suppression (87.6 ± 10.0%) in response to the bright light stimulus. Melatonin levels remained attenuated for 50-min after termination of the light stimulus (P < 0.008). Furthermore, melatonin levels did not return to 50% of those observed in the dim light condition 50-min after the light exposure for 7/10 children. Our findings demonstrate a robust light-induced melatonin suppression response in preschool-age children. These findings have implications for understanding the role of evening light exposure in the development of evening settling difficulties and may serve as experimental evidence to support recommendations regarding light exposure and sleep hygiene practices in early childhood.

Keywords: Circadian; light; melatonin suppression; preschool children; sleep.

Figure 1

Experimental Protocol. Actogram for a 4‐year‐old participant wearing an Actiwatch Spectrum. Black tick marks represent activity and yellow line represents light exposure in lux (scale 0.1 lux–200,000 lux). Clock hour is indicated on the x‐axis and day of study on the y‐axis. The dark bar on the x‐axis represents this individual subject's sleep interval (time in bed; 20:00–6:00). On days 1–5, children followed a strict sleep/wake schedule. On day 6, children entered dim light conditions (<15 lux; denoted by gray shading) 1‐h before the start of saliva sampling, where they remained until bright light exposure (~1000 lux; denoted by yellow shading) on day 7. Subjects returned to dim light conditions for 50‐min following the bright light stimulus. Times of saliva sampling are denoted by the blue line on days 6 and 7.

Figure 2

Melatonin Area Under the Curve (AUC) for Dim and Bright Light Conditions. Melatonin AUC is shown for the duration of the bright light stimulus (bright light condition) and at the same relative clock times in the dim light condition for each individual subject. AUC was lower in the bright light condition for all subjects.

Figure 3

Melatonin Suppression. Average melatonin profile in the dim light exposure night and bright light exposure night. Error bars represent standard error. Mean melatonin suppression was 87.6 ± 10.0% (M±SD). Melatonin levels in samples taken 20‐min before the start of bright light exposure were not significantly different between conditions (P = 0.65). Melatonin levels were significantly lower in samples taken at 10‐, 30,‐ and 50‐min after the start of bright light exposure in the bright light versus the dim light condition (*P ≤ 0.008; Bonferroni correction). Compared to the dim light condition, melatonin levels in the bright light condition remained lower 20‐ and 50‐min after children returned to dim light.