Single and aggregate salivary cortisol measures during two schooldays in midadolescent girls and boys

The hypothalamic-pituitary-adrenal (HPA) axis, including its regulation of cortisol, is central to bodily functioning and salivary cortisol is a commonly used biomarker that reflects the functioning of the HPA axis. However, knowledge of diurnal cortisol rhythms in healthy adolescents is limited and few studies have examined patterns in midadolescent girls and boys across single and aggregate cortisol measures. To fill this gap, the present study investigated single and aggregate cortisol measures reflecting diurnal rhythms in 14 to 16-year-old girls and boys. Self-administered salivary samples from 79 girls and 42 boys were collected during two schooldays at four timepoints: (a) immediately at awakening, (b) 30 min after waking up, (c) 60 min after waking up, and (d) at 8:00 p.m. Additionally, diary data including time of awakening, sampling times, and other potential confounders were analyzed. As for single measures, both girls and boys exhibited a typical diurnal cortisol profile with high levels in the morning that decreased throughout the day. However, girls had higher morning cortisol than did boys with significant differences at time of awakening, and at 30 and 60 min postawakening. For the aggregate measures, girls had a larger total level of cortisol in terms of cortisol awakening response (CARG ), area under the curve (AUCG ), and rise over run (slopeawake to last ), while no differences emerged for reactivity measures. Taken together, these findings suggest differences in single and aggregate cortisol measures between midadolescent girls and boys. Such differences in diurnal cortisol between pubertal girls and boys may play a role for the differential health trajectories typically found among adult women and men.