title: 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.
authors: a Laboratório de Cronobiologia e Sono do Hospital de Clínicas de Porto Alegre (HCPA) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.|b Programa de Pós-Graduação em Psiquiatria e Ciências do Comportamento, UFRGS , Porto Alegre , Brasil.
authors: Alicia
authors: A
authors: Carissimi
authors: a Laboratório de Cronobiologia e Sono do Hospital de Clínicas de Porto Alegre (HCPA) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.
authors: Alessandra Castro
authors: AC
authors: Martins
authors: a Laboratório de Cronobiologia e Sono do Hospital de Clínicas de Porto Alegre (HCPA) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.|b Programa de Pós-Graduação em Psiquiatria e Ciências do Comportamento, UFRGS , Porto Alegre , Brasil.
authors: Fabiane
authors: F
authors: Dresch
authors: c Programa de Pós-Graduação em Ciências Biológicas: Fisiologia, UFRGS , Porto Alegre , Brasil.
authors: Lilian Corrêa
authors: LC
authors: da Silva
authors: d Child and Adolescent Mood Disorders Program , University of Texas Health Science Center at Houston , TX , USA.
authors: Cristian Patrick
authors: CP
authors: Zeni
authors: a Laboratório de Cronobiologia e Sono do Hospital de Clínicas de Porto Alegre (HCPA) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.|b Programa de Pós-Graduação em Psiquiatria e Ciências do Comportamento, UFRGS , Porto Alegre , Brasil.|e Departamento de Psiquiatria e Medicina Legal da Faculdade de Medicina, UFRGS , Porto Alegre , Brasil.
authors: Maria Paz
authors: MP
authors: Hidalgo
mesh_terms: D000293:Adolescent; D001938:Brazil; D002648:Child; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D012574:Schools; D012890:Sleep / Q000502:physiology*; D013334:Students; D011795:Surveys and Questionnaires; D013997:Time Factors
chemical_list: D008550:Melatonin; D006854:Hydrocortisone
keywords: Behavior problems; child behavior check list; circadian rhythm; hormones; school start time