0339 Where Does the Time Go? Reported Activities Around the DLMO in Older Adolescents

Abstract

Abstract Introduction Older adolescents show heightened alertness in the evening close to the time of their Dim Light Melatonin Onset (DLMO), a time when the circadian system is most responsive to delaying light. We examined reported activities of adolescents around the time of their DLMO. Methods Forty-six adolescents (14.2-17.9 years; 24 females) who reported ≤7 h sleep on school nights and late bedtimes (school-night ≥ 23:00; non-school night ≥ midnight) slept at home on their usual school-year sleep schedule for 2 weeks. Participants reported their main activity via text message every hour from 16:00 until self-selected bedtime. After these 2 weeks, their DLMO was measured. We examined reported activities in the hour around the DLMO and the 2 hourly responses that followed on weeknights (Sunday-Thursday) to determine the most common activities (n=1380 responses). Logistic regression tested whether frequency of activities predicted whether a participant’s DLMO fell within the earliest (n=15; 19:31 ± 00:44), middle (n=16; 20:49 ± 00:20), or latest (n=15; 22:29±1:15) tertile. Results Overall, reported activities that consumed the most time were cell phone use (19.5%), homework (18.3%), and watching TV (15.1%). Adolescents who reported more homework, were more likely to have a DLMO in the middle tertile compared to the earliest and latest tertiles. Cell phone use was least likely in adolescents in the earliest DLMO tertile. TV watching did not predict DLMO group. Conclusion Adolescents who had the earliest DLMOs spent less time on their phones when light has the greatest delaying effect. These data may indicate that light from cell phone screens may delay circadian phase in this age group. Alternatively, cell phone use may be more likely if adolescents cannot fall asleep due to a later circadian cue for sleep onset. Support R01 HL112756 (Crowley)