Afternoon School Start Times Are Associated with a Lack of Both Social Jetlag and Sleep Deprivation in Adolescents.

The delayed circadian timing of adolescents creates a conflict with early school start times (SSTs). We used wrist actimetry to compare sleep parameters and routine nighttime activities in middle school students attending either a morning (0700 to 1200 h) or an afternoon (1230 to 1730 h) school shift. On school days, students from both shifts ( = 21 for morning shift, = 20 for afternoon shift, ages 12-14 years) had a similar sleep onset, but morning-shift students had an earlier sleep offset and a 1 h 45 min shorter sleep duration than their afternoon peers, who slept the recommended 8 to 10 h of daily sleep. Only morning-shift students had afternoon naps, but this afternoon sleep was not sufficient to overcome sleep deprivation. On weekends, sleep onsets and offsets did not differ between shifts. Because only morning-shift students woke up later and slept longer (2 h 3 min) on weekends, they were also the only ones who experienced social jetlag. Daily surveys on their nighttime (from 1800 to 0600 h) activities indicated there was no difference between shifts in the time spent on leisure or using electronic media during school days, but students from both shifts spent more time in these activities during the weekend. Our study confirms that early SST in adolescents is associated with sleep deprivation and suggests that schedules that start much later than typically considered may be needed to eliminate sleep deprivation in adolescents.