School Commute Time, Chronotype, and HPA Axis Functioning during Adolescence

• In Event: Poster Session 14
  In Poster Session: PS 14 Topic - Biological Processes: Psychophysiology

Abstract

Hypothalamic pituitary adrenal gland (HPA) axis functioning, as measured by cortisol activity, has been linked with daily demands during adolescence (e.g. Arbel et al., 2017, Chiang et al., 2016). A ubiquitous, yet understudied, daily demand for youth is the commute to school, which may be associated with cortisol secretion as demonstrated in prior studies that have focused on adults and the work commute (e.g. Evans & Wener, 2006). Adolescents need to marshal their physical and mental resources early in the morning to prepare for the school commute, and this repeated process may be more demanding for those with longer commutes which could result in repercussions for the HPA axis. This effect could be pronounced in youth who naturally engage in later bed and wake times characteristic of evening chronotypes (e.g. Hagenauer & Lee, 2012). We hypothesized that longer school commute times would be associated with HPA axis dysfunction as indexed by a heightened cortisol awakening response (CAR) and flattened diurnal slope. Additionally, given that the HPA axis follows a diurnal rhythm and adolescence is marked by changes in the circadian rhythm, known as chronotype, we hypothesized that more evening chronotype adolescents (those with later bed and wake times) would evince poorer HPA axis functioning in the face of long school commute times.
Adolescents (N=269; Mage=16.38 years; SDage=0.74; 58.33% female) provided timely saliva samples for the calculation of CAR and diurnal slope, completed up to 8 nights of sleep actigraphy, and self-reported school commute time. Multilevel models with days nested within adolescents were used to examine whether CAR and diurnal slope vary as a function of commute time on school days. Models assessed the effect of the CommuteTime×SchoolDay interaction and examined whether the effect of commute time varies as a function of adolescents’ chronotype by including a CommuteTime×Chronotype interaction.
Results suggested that the association of commute time with CAR varied by school day, such that adolescents with a longer commute times had a steeper CAR on school days but not on non-school days (Figure 1). Adolescents with longer commute times had flatter diurnal slopes, although this association did not vary with school day (Table 1, Model 1 for Diurnal Slope). Findings demonstrate heightened CAR, but not flattened diurnal slope, among average to evening chronotype youth with longer school commute times (see Table 1, Model 2 for CAR).
The current study extends the literature by showing that school commute time is also a unique daily demand that relates to HPA axis dysfunction via heightened CAR and flatter diurnal slope in adolescence. Evening chronotypes may mount a higher CAR in preparation for the school day since it is misaligned with their circadian rhythm. This study highlights how longer commute times relate to HPA axis function, particularly for evening chronotype youth, and this may have implications for mental health among youth given previous work linking HPA axis dysfunction with depression in youth (Kuhlman et al., 2017; 2020).

Authors

• Maira Karan, University of California - Los Angeles
  Presenting Author

• Danny Rahal, University of California - Los Angeles
  Non-Presenting Author

• David M. Almeida
  Non-Presenting Author

• Julienne E. Bower, University of California, Los Angeles
  Non-Presenting Author

• Michael R. Irwin, University of California, Los Angeles
  Non-Presenting Author

• Heather McCreath, University of California, Los Angeles
  Non-Presenting Author

• Teresa Seeman, University of California, Los Angeles
  Non-Presenting Author

• Andrew J Fuligni, University of California - Los Angeles
  Non-Presenting Author