Effect of Delaying School Start Time on Sleep Quality, Emotions, and Performance in Korean Adolescents

Background and Objective The purpose of this study was to investigate the effect of delaying school start time on sleep quality, emotions, and performance in Korean adolescents. Methods Data were collected in two months and 12 months after delaying school time, each using self-administered questionnaires for 238 students at a middle school in Gyeonggi province. Questionnaires consisted of demographic data and various sleep and emotion related scales, including the Pittsburgh Sleep Quality Index (PSQI). Students were divided into two groups, of increased or decreased total sleep time (TST). Results In both groups, sleep duration, global PSQI score, and sleep efficiency significantly improved in 12 months, compared to two months' data. There was significant improvement in depression, stress, behavioral aggression, and verbal aggression in the increased TST group. The increased TST group showed advancement in subjective feeling of happiness, and number of times students are late for school, between baseline and 12 months. The decreased TST group showed significant differences between baseline and 12 months in seven categories of subjective life quality/emotions in school, including subjective feeling of happiness, concentrating in classes, and anger. Conclusions After school start time was delayed, many adolescent's TST relatively decreased on school nights. However, students whose TST increased, showed reduction in depression, stress, and behavioral/verbal aggression. Students whose TST decreased also reported reduced negative affect, and significant improvement in subjective emotions and school performance. Delaying school start time may be beneficial, in improving mental health and quality of life of students. Key words: Adolescent, School time, Sleep quality, Depression, Emotion