School commute time, chronotype, and altered HPA axis functioning during adolescence.

Hypothalamic pituitary adrenal gland (HPA) axis functioning has been linked with daily demands during adolescence. A ubiquitous, yet understudied daily demand in the lives of youth is the commute to school, which may be associated with the diurnal rhythm of cortisol as demonstrated in prior research among adults. The current study hypothesized that longer school commute times would be associated with altered HPA axis functioning as demonstrated by a heightened cortisol awakening response (CAR) and flatter diurnal slope. Additionally, given that the HPA axis follows a diurnal rhythm and adolescence is marked by changes in the circadian rhythm, adolescents with a more evening chronotype were hypothesized to evince even more altered HPA axis functioning in the face of long school commute times. A total of 269 adolescents (M = 16.38 years, SD = 0.74) provided saliva samples at wake, 15-min. post-wake, and 30-min. post-wake for the calculation of CAR and at dinnertime and bedtime for the calculation of diurnal slope, completed up to 8 nights of sleep actigraphy, and self-reported school commute time. Results suggest that more evening chronotype youth with longer school commute times evince a higher CAR, but not an altered diurnal slope. The present findings may have implications for adolescent mental health as higher CAR has been associated poor mental health and heightened stress.