Directors: Antonio M. Battro and Kurt W. Fischer
Program officer: María Lourdes Majdalani
Sleep and daytime functioning of adolescents on a two-shift school schedule
Early school start time restricts wake-up time of adolescents in many countries worldwide. Since adolescents generally tend to go to sleep late in the evening, due to biological and psychosocial changes typical for adolescence, on school nights they obtain less than minimally recommended 8.5 hours of sleep. For majority of Croatian adolescents school is scheduled in two shifts. One week school starts in the morning, usually at 08:00 hours, the next week in the afternoon, usually at 14:00 hours, and the weekends are off. Bearing in mind the public health recommendations regarding minimally required sleep and regularity of sleep patterns we conducted two studies. The studies aimed (1) to examine the effects of shifting school schedule on sleep patterns and sleep duration and (2) to assess the relative predictive importance of sleep characteristics for adolescents daytime functioning.
In a survey study 2365 students (52 % females) from 5th to 8th grades of elementary schools and from 1st to 4th grades of high schools in Zagreb were examined. The modal age ranged from 11 yrs for the youngest grade of elementary school to 18 yrs for the oldest grade of high school. Sleep characteristics and scores on the Morningness-Eveningness scale for children were collected by means of the Croatian version of School Sleep Habits Survey (Wolfson AR, Carskadon M. Child Development 1998;69:875-87). The same survey was used to assess indices of daytime functioning: scores on the Sleepiness scale and the Depressed Mood Scale, number of injuries in a previous six-month period and self reported school grades. In a diary study 97 students (57% females) from 2nd grades of high schools (modal age 16 yrs) were observing their sleep patterns and daytime sleepiness over two school weeks with respective weekends. One week the school was scheduled in the morning and the other in the afternoon.
The results of our study indicate beneficial effects of two-shift school schedule regarding fulfillment of sleep need of adolescents – even to the extent that sleep duration on afternoon schedule might match the one on weekend. Pronounced irregularity of sleep patterns between morning and afternoon schedules did not seem to have any negative impact on indices of daytime functioning of adolescents. The most consistent and relatively most important predictor of good daytime functioning proved to be the preferred morning phase. Out of indices of sleep irregularity, only the relatively more pronounced shift of bedtime on weekend was implied as a consistent negative predictor of daytime functioning, although of quite a small importance. Since shorter sleep on morning schedule contributed to prediction of measures of daytime functioning (with the exception of school grades), the issue of early school start is still not resolved with two-shift school schedule. Further studies will examine Croatian adolescents attending school only in the morning shift in order to determine whether different opportunities for paying off the sleep debt in the one- and two-shift school systems impact sleep on morning schedule, as well as whether daytime functioning differs between the school system.