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.

Light Modulation of Human Clocks, Wake, and Sleep

“…Exposure to shorter wavelengths of light in the evening/night is known to elicit acute alerting effects and prolonged sleep latencies (as shown in young adults e.g., [61] and young children [99]), reduce REM sleep duration and suppress slow wave activity (SWA) during the first NREM/REM sleep cycle [63,64]. On the other hand, evening exposure to longer wavelengths of light was shown to have sleep promoting effects by shortening sleep onset and increasing sleep duration in rodents [100].…”

Potential circadian and circannual rhythm contributions to the obesity epidemic in elementary school age children

“…Further, much of what is known about human seasonality and entrainment to natural and artificial modern lighting has come from studies with adults [65,[111][112][113]. Children appear to be more sensitive to light exposure [4] due to more transparent ocular lenses and larger pupils [114]. As a result, studies are needed to understand how children's circadian systems, and particularly the melatonin rhythms respond under natural lighting conditions (i.e., camping) and modern lighting conditions across seasons, geographic locations and in school and summer holiday environments.…”

“…As a result, studies are needed to understand how children's circadian systems, and particularly the melatonin rhythms respond under natural lighting conditions (i.e., camping) and modern lighting conditions across seasons, geographic locations and in school and summer holiday environments. Because children are more sensitive to the effects of light [4], they may be able to maintain a circannual rhythm even when adults do not. Also the nature of the school and school holiday environment may be different enough from the typical adult office worker that it may affect their circannual rhythms in unknown ways.…”

“…Nine percent showed evidence of this transition during the summer holiday after kindergarten while another 9% started during the summer holiday after 2nd grade, creating a clear window for prevention efforts during early elementary school. Seasonal weight gain, driven by circannual changes in the environment (i.e., changes in the length and timing of daylight and temperature over the course of a year) is common within the animal kingdom where it confers evolutionary advantage, via preparation for winter or reproduction [3,4]. Whether or not seasonal weight gain provided pre-industrialized humans with advantage, it currently confers evolutionary disadvantage by contributing to increasing rates of overweight and obesity [2,[5][6][7].…”

Chronotype-Dependent Changes in Sleep Habits Associated with Dim Light Melatonin Onset in the Antarctic Summer

“…The dim light melatonin onset (DLMO, the start of the evening rise of melatonin in plasma or saliva) is the best proxy of the functioning of the circadian clock in humans [10,16]. The DLMO itself is affected by light, so it can be either advanced by bright light exposure in the morning [17][18][19][20] or delayed by light exposure during the evening [21,22]. Likewise, it is clear that seasonal changes in day length affect the duration and phase of the nocturnal melatonin pulse [23,24].…”