High sensitivity of melatonin suppression response to evening light in preschool‐aged children

Abstract

Light at night in adults suppresses melatonin in a nonlinear intensity-dependent manner. In children, bright light of a single intensity before bedtime has a robust melatonin suppressing effect. To our knowledge, whether evening light of different intensities is related to melatonin suppression in young children is unknown.Healthy, good-sleeping children (n = 36; 3.0-4.9 years; 39% male) maintained a stable sleep schedule for 7 days followed by a 29.5-h in-home dim-light circadian assessment (~1.5 lux). On the final night of the protocol, children received a 1-h light exposure (randomized to one of 15 light levels, ranging 5-5000 lux, with ≥2 participants assigned to each light level) in the hour before habitual bedtime. Salivary melatonin was measured to calculate the magnitude of melatonin suppression during light exposure compared with baseline levels from the previous evening, as well as the degree of melatonin recovery 50 min after the end of light exposure. Melatonin levels were suppressed between 69.4% and 98.7% (M = 85.4 ± 7.2%) during light exposure across the full range of intensities examined. Overall, we did not observe a light intensity-dependent melatonin suppression response; however, children exposed to the lowest quartile of light intensities (5-40 lux) had an average melatonin suppression (77.5 ± 7.0%) which was significantly lower than that observed at each of the three higher quartiles of light intensities (86.4 ± 5.6%, 89.2 ± 6.3%, and 87.1 ± 5.0%, respectively). We further found that melatonin levels remained below 50% baseline for at least 50 min after the end of light exposure for the majority (62%) of participants, and recovery was not influenced by light intensity. These findings indicate that preschool-aged children are highly sensitive to light exposure in the hour before bedtime and suggest the lighting environment may play a crucial role in the development and the maintenance of behavioral sleep problems through impacts on the circadian timing system.

Evening Light Intensity and Phase Delay of the Circadian Clock in Early Childhood

“…Analyses were run including and excluding this participant, with no change to the results. See Hartstein et al (2022) for calculations and findings on acute melatonin suppression during the light exposure. The circadian phase shift was calculated as the difference between baseline DLMO (Day 8) and final DLMO (Day 10) the evening after the light exposure.…”

“…DLMO was calculated as the linear interpolated clock time at which melatonin levels crossed 4 pg/mL, provided they remained above the threshold for at least two consecutive samples (Carskadon et al, 1997; Deacon and Arendt, 1994). One child had consistently high melatonin levels and therefore a threshold of 10 pg/mL was used to calculate DLMO values (Crowley and Eastman, 2017; Hartstein et al, 2022). Analyses were run including and excluding this participant, with no change to the results.…”

“…On Day 9, participants received a 1 h light exposure in the hour before their habitual bedtime. Children were randomly assigned to a single light intensity between 5 and 5000 lux in the angle of gaze (see Hartstein et al, 2022, for the rationale behind the chosen intensities and the photometric properties of each experimental light condition). Children sat at a small table with a flat, tunable LED panel (5000 K; Beghelli, USA), and researchers directed children's gaze downward to the light source by playing with translucent toys or coloring on transparent overhead sheets.…”

“…We previously demonstrated that preschool-aged children had robust and sustained suppression of melatonin in response to a bright (1000 lux) 1-h light exposure in the hour before bedtime (Akacem et al, 2018). Furthermore, we previously reported high suppression of melatonin across a wide range of intensities and regardless of the individual circadian timing of the light exposure (Hartstein et al, 2022). In addition, previous findings indicate that children’s circadian systems are more sensitive to evening light than those of adults (Higuchi et al, 2014).…”

CYP1B1: A Novel Molecular Biomarker Predicts Molecular Subtype, Tumor Microenvironment, and Immune Response in 33 Cancers

“…The melatonin is further metabolized into 6-hydroxymelatonin (6OH-MEL) by human cytochrome P450 family [ 4 ]. Evidence shows that various biological properties of melatonin, such as the circadian clock [ 5 , 6 , 7 ], sleep regulation [ 8 , 9 ], anti-inflammatory properties [ 10 , 11 , 12 ], immune modulation [ 13 , 14 , 15 ], and anti-cancer activities [ 16 , 17 , 18 ], have been well revealed. Nevertheless, the clinical and immunological function of the cytochrome P450 family in cancer remains unclear.…”