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

Sep 1, 2016Chronobiology international

School start times are linked to melatonin and cortisol levels in children and teens

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Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

Morning school start time is associated with decreased secretion of melatonin in children and adolescents.

Morning melatonin levels are significantly positively correlated with sleep midpoint on weekdays and weekends.
Afternoon melatonin levels are positively correlated with sleep midpoint on weekends for students with morning school start times.
Night melatonin levels in students with afternoon school start times are negatively correlated with sleep midpoint on weekdays.
Cortisol secretion does not correlate with circadian sleep parameters in any school time group.
The correlation between melatonin secretion and circadian sleep parameters may depend on the presence of psychiatric symptoms.

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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.

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

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