Hair Cortisol Concentration and Mental Health During Childhood and Adolescence: evidence of higher cortisol concentration in ADHD symptoms in a large Brazilian population-based birth cohort

Background: Childhood and adolescence are pivotal for mental health. The hypothalamic-pituitary-adrenal axis is the primary stress system, with chronic activation measurable via hair cortisol concentration (HCC), indicating long-term stress exposure. While elevated HCC is linked to adult mental health, its role in youth remains unclear. This study aims to assess the association between mental health symptoms in childhood and adolescence and HCC levels at age 15 in a Brazilian population-based cohort. Methods: We analyzed data from the 2004 Pelotas Birth Cohort, which includes 4,231 children followed from birth. At ages 6, 11 and 15 years, mental health symptoms were assessed using the Strengths and Difficulties Questionnaire (SDQ). At age 15, HCC was measured from 3 cm hair samples, and analyzed as ln (pg/mg). Linear regression models examined associations between HCC and SDQ scores, adjusting for perinatal variables, demographic factors, family income, maternal characteristics, maternal depression, harsh parenting exposure, hair traits, and corticosteroid use. The regression coefficient was exponentiated to improve interpretability. Results: SDQ total difficulties and conduct problems at age 6 were associated with HCC at age 15 in adjusted models (p<0.05). Hyperactivity/inattention symptoms at ages 6 (β=1.009 [1.001;1.018]) and 11 (β=1.013 [1.004;1.022]) were associated with HCC in the adjusted models. At age 15, the association between hyperactivity/inattention and HCC was associated with HCC in the partially adjusted model. (β=1.009 [1.000;1.017]). Conclusions: These associations emphasize the links between mental health and chronic stress over time, mainly an association between Attention-Deficit/Hyperactivity Disorder symptoms and higher concentration of HCC.