Effect of morning school schedule on sleep and anthropometric variables in adolescents: a follow-up study

The aim of this study was to assess whether the shift from afternoon to morning classes reduces the duration of sleep and whether this reduction has any relation to body fat measurements. This is a follow-up study in which students (n = 379), 12.4 (SD(+/-)0.7) yrs old, were evaluated before and after the school schedule shift, with a 1-yr interval between the first and second data collections. Adolescents were divided into two groups: an afternoon-morning group (students who shifted from afternoon to morning classes) and an afternoon-afternoon group (students who remained in afternoon classes). The morning schedule of classes lasted from 07:30 and 12:00?h, and the afternoon schedule of classes lasted from 13:00 and 17:30?h. Self-reported bedtime, wake-up time, and time-in-bed were obtained. Body mass index, waist circumference, and body fat percentage were obtained by direct measures. The results showed a reduction of time-in-bed during weekdays for those students who changed to the morning session (p < .001). Analysis of covariance (ANCOVA) for repeated measures of anthropometric differences between afternoon-afternoon and afternoon-morning groups showed no effect of the school schedule change on weight gain. In conclusion, the time-in-bed reduction in the period analyzed cannot be considered to be a mediating factor to modifications in overweight anthropometric indicators.