Effect of Sunfight Exposure in the Morning on Sleep-Wake Cycle and Daytime Sleepiness of Adolescents

*Corresponding author e-mail: ivanise@cb.ufrn.br Introduction: Adolescents present biological and social pressures to a phase delay that is counterposed by early school schedules. At vacation, the sleep schedules change making it difficult the return to school. As a consequence they have short sleep duration and sleep irregularity between school and no school days leading to daytime sleepiness and cognition performance deficit. As light promotes phase advances between the end of rest and the start of activity in humans, problems can be minimized by exposure to morning sunlight. Objective: To evaluate the effect of sunlight exposure in the morning on the sleep-wake cycle (SWC) and sleepiness of adolescents in the return to the classes after mid-year vacation. Methods: 83 high school students volunteers aged 15 ± 0.5 took part in 2 stages: 1a) Characterization about sleep knowledge and habits; 2a) SWC and sleepiness evaluation for two consecutive weeks after mid-year vacation. The SWC was assessed by sleep log and the sleepiness levels were evaluated by the Karolinska Sleepiness Scale (KSS), on 5 times: wake-up time, 8h, 11h, 14h and bedtime. Besides, subgroups underwent a psychomotor vigilance test on weekdays at 8h and 11h. At the second week after mid-year vacation the sunlight intervention group (n=45) attended the first class (7:15-8:00 h) at shadow in an outdoor environment exposed to sunlight (11.500 ± 4.800 lux) while the control group (n=38) stayed in usual classroom (256 ± 96 lux). Results: The intervention group anticipated the bedtime from 23h48min to 23h25min and increased sleep duration in 16 minutes on weekdays. The sleepiness levels, measured by the KSS, showed no difference between the two weeks for both groups, but the PVT detected a decrease in reaction time at 11hs in the intervention group. Naps frequency diminished on weekdays from 46% to 31% on the intervention group. Irregulatity remained for bedtime, but decreased to wake-up time for both groups. Conclusion: sunlight exposure in the morning advanced the SWC and increased alertness at 11hs. Thus, this intervention can be used as a school procedure to help students to adapt their sleep-wake cycle on the return to school. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil