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.
Highlights
The human circadian clock, localized to the suprachiasmatic nucleus (SCN) of the anterior hypothalamus, is strongly influenced by light (Czeisler et al 1981; Ralph et al 1990; Duffy and Wright 2005)
Information on the light/dark cycle is communicated to the circadian clock through direct input from retinal photoreceptors via the retinohypothalamic tract (Moore and Card 1985; Johnson et al 1988)
This pathway begins with efferent projections from the SCN to the paraventricular nucleus (PVN), which sends descending projections to the intermediolateral cell column (IML) of the spinal cord
Summary
The human circadian clock, localized to the suprachiasmatic nucleus (SCN) of the anterior hypothalamus, is strongly influenced by light (Czeisler et al 1981; Ralph et al 1990; Duffy and Wright 2005). Secretion of melatonin is regulated by a multisynaptic pathway originating from the SCN and terminating at the pineal gland (Moore and Klein 1974; Teclemariam-Mesbah et al 1999; Kalsbeek et al 2006). This pathway begins with efferent projections from the SCN to the paraventricular nucleus (PVN), which sends descending projections to the intermediolateral cell column (IML) of the spinal cord. Preganglionic sympathetic neurons project to the superior cervical ganglion (SCG) This synaptic pathway terminates with postganglionic sympathetic nerve fibers that project onto the pineal gland (Borjigin et al 1999).
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