The influence of a permanent double-shift school start time on adolescent sleep and chronotype across different age groups

ABSTRACT

The main objective of this study was to explore the differences in sleep habits and chronotype across different age groups in Mexican adolescents attending a permanent double-shift school system. This cross-sectional study consisted of 1,969 (1,084 girls) students from public elementary, secondary, and high schools, as well as undergraduate university students from Mexico. Age range was 10–22 [15.33 ± 3.28 (mean ± SD)] years, 988 morning shift and 981 afternoon shift students. Questions regarding usual self-reported bedtime and rise time were collected, and from that, estimates for time in bed, midpoint of sleep, social jetlag, and chronotype were evaluated. Afternoon shift students reported later rise times, bedtimes, midpoint of sleep, and longer time in bed on school days than morning shift students, as well as less social jetlag. Overall, afternoon shift students reported a later chronotype than morning shift students. Peak lateness of chronotype in afternoon shift students was at age 15, with girls peaking at age 14 and boys at age 15. Meanwhile, morning shift students reported peak lateness of chronotype around age 20. In this study, adolescents from different age ranges attending an extremely delayed school start time reported adequate sleep compared with adolescents attending a fixed morning school start time. In addition, the analysis presented in this study seems to suggest that the peak of late chronotype may be influenced by school start times.

KEYWORDS:

• School shift
• sleep
• chronotype
• school start times
• adolescence

Acknowledgments

The authors would like to thank all the schools’ administrators, parents, and students who participated in this study. JFDM is supported by the Spanish State Plan for Scientific, Technical and Innovation Research, the Spanish Ministry of Science and Innovation (Grant PID2020-116600RB-100). AAP is supported by a fellowship from the Sara Elizabeth O’Brien Trust, Bank of America Private Bank, Co-Trustees. JFD is supported in part by grants from the US National Institutes of Health [R01 AG044416, R01 HL148704, R01 DK127254].

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No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.