Low hair cortisol concentration predicts the development of attention deficit hyperactivity disorder

Low activity of the hypothalamic-pituitary-adrenal axis (HPAA) resulting from genetic and early environmental factors has been thought to indicate risk for the development of attention deficit hyperactivity disorder (ADHD) and externalizing disorders. However, longitudinal research on this issue is scarce. We analyzed whether hair cortisol concentration (HCC), i.e. accumulated long-term HPAA activity, predicts the development of ADHD between preschool and school age.

A community-based sample of 126 children was assessed at the ages of 4, 5 and 8 years. ADHD and symptoms of oppositional defiant and conduct disorder (ODD/CD), callous unemotional (CU) traits, and internalizing symptoms were measured by clinical parent interviews and parent and teacher questionnaires. HCC was analyzed in the most proximal 3-cm scalp hair segment using luminescence immunoassay.

Low HCC at preschool age predicted an increase in ADHD symptoms between preschool and school age while adjusting for gender of child, maternal education level, and internalizing symptoms (F_(1,119) = 6.5; p = .012). The prediction held after additionally adjusting for ODD/CD symptoms and CU traits (F_(1,116) = 4.1; p = .045). The same was true for the prediction of the ADHD diagnosis at the age of 8 years (Chi²₍₁₎ = 7.3; p = .007). The prediction of ADHD was mainly based on the presentation of inattention symptoms (F_(1,119) = 7.4, p = .008).

Low HCC in preschool children indicates an increased risk of developing ADHD at school age. In future research, it would be of theoretical and clinical importance to further circumscribe this HCC-related developmental pathway and track its further course of development.