Shingo Noi

Prior light exposure can influence the magnitude of melatonin suppression in response to evening light, even within the same individual. We examined whether light-induced melatonin suppression in school-aged children differed before and during a camp with approximately two weeks of exposure to a natural light-dark cycle. We also explored interindividual variation in melatonin suppression and its associations with circadian phase, habitual sleep timing, and daytime light exposure. Twenty-one healthy children aged 9—14 years underwent evening light experiments at the start of camp (Pre-camp session) and approximately two weeks later (Camp session). Melatonin suppression was calculated by comparing the area under the melatonin concentration curve between the evening light condition (200 ± 30 lx, 5000 K) and the dim light condition (< 30 lx, incandescent lamps), with integration starting at dim light melatonin onset (DLMO). We assessed sleep habits from 14-day sleep diaries before camping and measured wrist-level illuminance during camping. We examined associations using Spearman correlations and compared Pre-camp and Camp melatonin suppression using a paired t-test. Melatonin suppression did not differ significantly between Pre-camp and Camp sessions (p = 0.21). Greater suppression in the Pre-camp session was associated with later DLMO (rho = 0.49, p = 0.028), but not with habitual sleep variables. In the Camp session, higher same-day geometric mean illuminance was associated with lower suppression (n = 15; rho = −0.58, p = 0.024), whereas 7-day light-exposure metrics were not. Mean melatonin suppression did not significantly change across the camping period. Meanwhile, children showed large interindividual variation in melatonin suppression, and circadian phase and recent daytime light exposure are candidate correlates of this variation in the responsiveness to the evening light.

Social restrictions associated with the COVID-19 pandemic have altered children’s movement behaviours and impacted their mental health. However, the influence of social restrictions on subjective health complaints remains inadequately understood. This study compared adherence to 24-hour movement behaviour guidelines and the prevalence of subjective health complaints during school closure and one year after reopening. We also examined how combinations of adherence to movement behaviour recommendations relate to subjective health complaints. A repeated cross-sectional survey was conducted at two points. The first survey in May 2020 included 1535 (766 boys and 769 girls) participants during school closures, while the second survey from May to July 2021 involved 1125 (583 boys and 542 girls) participants one year after school reopening. The questionnaire covered socio-demographics, physical activity, screen time, sleep, and subjective health complaints. Differences between periods were analysed using chi-square tests. Logistic regression models assessed the association between adherence to guidelines and subjective health complaints. During school closure, children were more likely to meet ‘only sleep’ recommendations and have irritability and lethargy symptoms. Irrespective of sex, those adhering to two or all three recommendations (excluding physical activity and screen time) had a lower risk of symptoms related to physical and mental pain, fatigue, irritability, and lethargy as compared to those who met none of the recommendations. Children should meet at least one physical activity or screen time recommendation in addition to sleep recommendations for subjective health. Strategies considering the priority of each movement behaviour are crucial, even during abnormal situations, such as pandemic-related social restrictions. This study offers insightful findings concerning children’s mental health issues during unprecedented and massive disasters or crises.

This study examined changes in physical activity (PA), sedentary behavior (SB), screen time, sleep, and executive function among Japanese preschoolers between COVID-19 pre-pandemic and pandemic periods, using cross-sectional and longitudinal data. Accelerometer data from 63 children aged 5–6 years were collected from three kindergartens in Tokyo, Japan, in late 2019 (pre-COVID-19). This was compared to the data of 49 children aged 5–6 years from the same kindergartens, collected in late 2020 (during COVID-19). Sixteen children in the pre-COVID-19 cohort also participated in the 2020 survey and provided data for the longitudinal analysis. The mean minutes of PA, SB, screen time, and sleep duration, as well as executive function, were compared between the pre- and during COVID-19 cohorts. After adjusting for school, sex, and accelerometer wear time, there were no significant differences in any of the measured outcomes between the two cohorts. However, the analysis of longitudinal data revealed significant increases in time spent in SB and on screens, and a decrease in light-intensity PA and sleep duration during the pandemic compared to the pre-pandemic period. Results suggest that, despite the COVID-19 pandemic, young children’s activity levels and SB did not significantly differ from pre-pandemic levels. However, school-aged children’s SB, light PA, and sleep time were affected, although this cannot be disentangled from the effects of the transition to school.

Background: It is known that the circadian rhythm phase in adults can be advanced in a natural light-dark cycle without electrical lighting. However, the effect of advanced sleep-wake timing according to the natural light-dark cycle on children’s circadian phase is unclear. We investigated the effects of approximately 2 weeks of camping life with little access to artificial lighting on children’s circadian phases. We also conducted an exploratory examination on the effects of wake time according to natural sunrise time on the manner of the advance of their circadian phases. Methods: Twenty-one healthy children (mean ± SD age, 10.6 ± 1.4 years) participated in a camping program with wake time (4:00) being earlier than sunrise time (EW condition), and 21 healthy children (10.4 ± 1.1 years) participated in a camping program with wake time (5:00) being almost matched to sunrise time (SW condition). Salivary dim light melatonin onset (DLMO) before the camping program and that after approximately 2 weeks of camping were compared. Results: DLMO was advanced by approximately 2 h after the camping program compared with the circadian phase in daily life in both conditions. In addition, the advances in DLMO were significantly correlated with mid-sleep points before the camp in both conditions (EW: r = 0.72, p < 0.01, SW: r = 0.70, p < 0.01). These correlations mean that the phase advance was greater for the children with delayed sleep habits in daily life. Furthermore, in the EW condition, mean DLMO after the camp (18:09 ± 0:33 h) was earlier than natural sunset time and there was no significant decrease in interindividual variability in DLMO. On the other hand, in the SW condition, mean DLMO after the camp (18:43 ± 0:20 h) matched natural sunset time and interindividual variability in DLMO was significantly lower than that before the camp. Conclusions: Camping with advanced sleep and wake timing under natural sunlight advances children’s circadian phases. However, DLMO earlier than sunset in an early waking condition may lead to large interindividual variability in the circadian rhythm phase.

This study aimed to clarify the situation of light exposure and examine the relationship between light exposure and bedtime/wake-up time during school days (SD), holidays (HD), and a long-stay camp period (CP) in Japanese children. After data cleaning, the final subjects were 29 children (10.2 ± 1.2 years old, 25 boys and 4 girls) who participated in paid long-term camp programs in the summers of 2019 and 2021. Data on light exposure, bedtime, and wake-up time were collected. The results of the comparison of the total high-intensity light exposure (HLE) hours for each survey period confirmed that HLE was high before the 18:00 zone in CP, and that for SD and HD were high after the 19:00 zone. Furthermore, the longer the total HLE hours before the 18:00 zone and the shorter those after the 19:00 zone were significantly earlier with both bedtime and wake-up time. These findings indicate that daytime and nighttime light exposure in children’s actual living environment is related to their bedtime and wake-up time, and that camping and going to school may be important factors to ensure children’s adequate daytime light exposure.

While wilderness programs are recognized as a feasible intervention to promote psychological independence in adolescence, little is known about physiological changes. The present study focused on oxytocin, a key hormone for social cognition and behavior, and investigated changes in OT concentrations during a wilderness program among adolescents. Twenty-one 4th–7th graders were separated from parents and immersed with adventures and challenges in the woodlands of Motegi, Tochigi Prefecture, Japan for 31 days, and dataset of 20 boys aged 9–13 years-old were used for analysis. OT concentrations in early morning saliva samples on days 2, 5, 8, 13, 18, 20, 21, 22 and 30 were determined using ELIZA. We performed multi-level regression analyses to compare the OT concentrations before and after solo and team-based survival challenges, and across the nine observational points, adjusting for potential covariates. We found that adolescents increased OT level in a situation where they needed others’ cooperation and support for survival (coefficient: 2.86, SE: 1.34, p = 0.033). Further, we found that adolescents gradually decreased their basal OT level during a long separation from parents (coefficient: −0.083, SE: 0.034, p = 0.016). A combination of these findings suggest the OT level may be a marker for psychological independence.

While limited evidence is available, preliminary studies highlight the potential health benefits of risky play. However, most of the studies have used subjective methods (i.e., questionnaires) to evaluate children’s risky play, which limits their validity and reliability. The purpose of the present study was to examine the relationship between the frequency of risky play and social behavior among Japanese preschoolers by using a valid and reliable method such as direct observation. A total of 32 Japanese preschoolers (71.4 ± 3.5 months old) participated in the study, and their social behaviors were measured by the Strength and Difficulties Questionnaire (SDQ). Data regarding the frequency of risky play was collected through direct observation. Results stated that, in a non-adjusted model, there was no significant association between children’s risky play and prosocial behavior. However, the association became significant after adjusting for covariates such as gender, parental employment status, and physical activity. In contrast, there was no significant association between children’s risky play and problem behavior (hyperactivity and aggression) after adjusting for covariates. In conclusion, covariates such as parental employment should be considered when examining the benefits of risky play.