Children’s hair cortisol as a biomarker of stress at school: a follow-up study

In a previous study, we examined hair cortisol concentrations (HCCs) in children when first entering elementary school (at 4 years). In this follow-up study, we examined their HCC when they entered third grade (at 6 years), where the more playful first grades proceed into a more formal learning setting. Participants were 30 6-year-old children (14 boys). Hair samples (≥5 cm) were collected 2 months after the summer holidays. Hair analysis was conducted using two 2-cm long segments, reflecting the first 2 months of school attendance in grade 3 (the scalp-near segment), and 2 months prior to the start in grade 3. Between these two sections, we left a gap of 1 cm to avoid overlap of periods (due to differences in hair growth rate). Children showed a significant increase in cortisol levels when they entered third grade. This increase was not associated with social fearfulness or academic achievement, but did show significant associations with inhibitory control: children with less inhibitory control had higher cortisol levels after entering third grade, and larger increases in cortisol than children with higher scores on inhibitory control. This suggests that the ability to inhibit or control impulsive responsivity is important for children’s stress regulation when making the transition to a more formal school environment