Sleep-wake habits and circadian preference in Mexican secondary school.

OBJECTIVE: The current study aimed to determine the differences between sleep-wake habits and circadian preference in Mexican adolescents attending classes at a morning shift or an afternoon shift.

METHODS: The sample consisted of 568 students of a secondary school in Reynosa, northeastern Mexico, of whom 280 were boys and 288 were girls (mean age 14.08 ± 0.72 years, age range 13-16 years). In the morning shift, 287 students attend classes on a schedule from 7:30 to 13:00 and the afternoon shift, 281 students, on a schedule from 13:20 to 19:00. Students completed a general information questionnaire, the Sleep Timing Questionnaire and the Spanish version of the Morningness-Eveningness Questionnaire.

RESULTS: The adolescents who attended the morning shift had earlier bedtime and waking time, but shorter sleep duration than those who attended the afternoon shift. Those oriented to eveningness had later bedtime, waking time, and a shorter sleep duration than those oriented to morningness. Two interactions were found between school shift and chronotype. First, with regard to waking time during weekdays, students who attended the afternoon shift and were oriented to eveningness woke up later than those who attended the morning shift and were oriented to eveningness; during weekdays, there were no differences between the waking time of morning-type and evening-type students who attended the morning shift. Second, with regard to sleep duration on weekdays, students who attended the morning shift and were oriented to eveningness had the shortest sleep duration. Furthermore, there were no differences between sleep duration on weekdays in evening-type and morning-type students of the afternoon shift.

CONCLUSION: Adolescents who attend classes in the morning shift and are oriented to eveningness are the most sleep deprived. Those who attend the afternoon shift will have optimal sleep duration, regardless of their circadian preference.