Effects of Daily Physical Activity Level on Circadian Rhythm of Oral Body Temperature and Melatonin in Children

Abstract

Recently, schoolchildren's bedtimes have gradually gotten later, and their total sleep time is being shortened in Japan. It is very important for them that they have sleep in sufficient quantities and suitable hours from the view point of growth and development. Exercise has been considered to be a synchroniser of human circadian rhythms. Therefore, an inactive lifestyle may cause retreatment of the circadian rhythms. There has been no report, to our knowledge, which has examined the relationships between the daily physical activity level and circadian rhythms in children. PURPOSE: To examine the effect of daily physical activity level on circadian rhythm of oral body temperature (OBT) and melatonin in children. METHODS: Fifty-three boys (aged 9–11) were evaluated for oral body temperature (OBT) and daily physical activity (DPA) over a one-week period. OBT was measured at waking time, 14:00, and bedtime. DPA was defined as number of daily steps determined using accelerometry. Melatonin concentrations in saliva at bedtime also were collected on two nights of weekday. The low DPA group (L) and high DPA group (H) were defined as 1SD above the mean DPA in all subjects, respectively. RESULTS: (see Table 1) There were no significant differences in waking time (L:6:35[SD 0:29] vs H:6:24[0:25]), bedtime (L:21:47[0:26] vs H:21:54[0:32]) or total sleeping time (L:532[24]min vs H:514[27]min) between L and H group. Thus, both group have the same social schedules, however, melatonin concentration at bedtime, and DPA were significantly higher in H versus L. An insufficient decline in bedtime OBT was observed in L versus H. There is also a significant positive correlation (r = 0.419, p<0.01, n = 53) between melatonin concentration at bedtime and DPA in all subjects. CONCLUSIONS: Our results suggest that a lower level of daily physical activity may be a cause in retreatment of OBT and melatonin circadian rhythm. Practical Applications:Increased daily physical activities in children would contribute to the synchronization of circadian rhythm.