2020 Volume 2020 Issue 87 Pages 20-28
It is well known that Japanese children have severe sleep problems and circadian misalignment. Many studies have found that sleep problems and circadian misalignment in children lead to not only increases in diurnal sleepiness and impairment in memory function, but also behavioral problems, long-term absentee, and suicidality. It has been reported that children who participate in a long-term camp exhibit improved melatonin secretion patterns. However, the factors that contribute to the improvement in melatonin secretion patterns during a long-term camp are unclear. Therefore, the purpose of the present study was to examine the living situations related to melatonin secretion patterns in free-living children. Forty-four 5th-grade children in an elementary school (22 boys and 22 girls) participated in the present study. Saliva melatonin was collected at 21 : 30 (night) and 6 : 30 (morning) at home. Based on night and morning saliva melatonin concentrations, we divided the participants with night > morning to the “morning-type group” and those with night ≤ morning to the “night-type group.” All participants completed a self-administered questionnaire consisting of items to obtain living situations information including physical activity, diurnal light exposure, dim light environment, use of electronic devices, and internet addiction disorder. As a result of the present study, children classified as the night-type group based on night and morning saliva melatonin concentrations showed a higher percentage than the morning-type group (72.7％, n＝32 and 27.3％, n＝12, respectively; p < 0.05). In addition, the total physical activity duration in a day in the morning-type group was significantly about 56％ longer than that in the night-type group [146.7±83.4 min and 94.2±63.3 min (mean±standard deviation), respectively; p < 0.05]. However, there was no association among melatonin secretion patterns and other living situations (diurnal light exposure, dim light environment, use of electronic devices, and internet addiction disorder). Our findings suggest that the living situation that is related to melatonin secretion patterns in free-living children is total physical activity duration in a day.
