School start time influences melatonin and cortisol levels in children and adolescents – a community-based study

Abstract

School start time influences sleep parameters. Differences between circadian sleep parameters on weekends and weekdays have been associated with obesity, sleep, and psychiatric disorders. Moreover, circadian rhythm dysregulation affects the secretion of some hormones, such as melatonin and cortisol. In the current study, we investigate the effect of school start time on cortisol and melatonin levels in a community sample of Brazilian children and adolescents. This was a cross-sectional study of 454 students (mean age, 12.81 ± 2.56 years; 58.6% female). From this sample, 80 participants were randomly selected for saliva collection to measure melatonin and cortisol levels. Circadian sleep parameters were assessed by self-reported sleep and wake up schedules and the Morningness-Eveningness Questionnaire. The outcomes, salivary melatonin and cortisol levels, were measured in morning, afternoon and night saliva samples, and behavior problems were assessed using the Child Behavior Checklist (CBCL). The main results revealed that morning school start time decreased the secretion of melatonin. Morning melatonin levels were significantly positively correlated with the sleep midpoint on weekdays and on weekends. Afternoon melatonin levels were positively correlated with the sleep midpoint on weekends in the morning school students. Conversely, in the afternoon school students, night melatonin levels were negatively correlated with the sleep midpoint on weekdays. Cortisol secretion did not correlate with circadian sleep parameters in any of the school time groups. In conclusion, school start time influences melatonin secretion, which correlated with circadian sleep parameters. This correlation depends on the presence of psychiatric symptoms. Our findings emphasize the importance of drawing attention to the influence of school start time on the circadian rhythm of children and adolescents.

Assessing Chronotypes by Ambulatory Circadian Monitoring

“…According to the chronotype, E-types presented the best exposure pattern, although they were still exposed mostly to indoor bright light. L-types spent most of their daytime underexposed to bright light, while their time in darkness during the night was shorter than for E-types, as has been previously published (Carissimi et al, 2016), probably due to the use of electronic devices (Cain and Gradisar, 2010; Chang et al, 2014; Touitou et al, 2016) until late at night in the L-type group. However, it is still unclear whether differences in voluntary light exposure between chronotypes, which could be explained by the sleep/wake pattern, are the cause or consequence of their circadian phase preference, although differences between them are minimized when both are exposed to natural light–dark cycles (Wright et al, 2013).…”

A critical review of melatonin assays: Past and present

“…There is no pretreatment of samples prior to assay. Melatonin levels in saliva collected at midday in normal children were between 6 and 11 pg/mL with this assay 72,73 while the threshold for calculating DLMO in adults was 10.4 pg/mL. 74 Some recent studies have however reported levels of 0.8-2 pg/mL in adults at 14:00 hours.…”

Sleep and Depressive Symptoms in the Morningness/Eveningness-Suicidal Ideation Relationship Depend on School Shift in Mexican Adolescents

“…However, with the recent body of research on the afternoon school shift [8][9][10][11]22], school start time cannot be considered as a synchronizer, but rather as a social mechanism that will determine the time when adolescents synchronize with the light-dark cycle [30], which is an important physical zeitgeber [31]. Interestingly, in the three studies that assess melatonin in school shifts, results have indicated that light-induced melatonin suppression appears first for adolescents in the morning shift, thus synchronizing their circadian rhythms at different times [32][33][34].…”