Hair cortisol concentration and neurocognitive functions in preschool children at risk of developing attention deficit hyperactivity disorder.

OBJECTIVE: Sex differences have been shown in the relation between hair cortisol concentration (HCC) and ADHD symptoms. As an extension of these findings, we analyze whether a child's sex modulates the associations between HCC and ADHD-related neurocognitive functions. METHODS: A community-based sample of 122 children was tested at age 4-5 (T1) and 8 (T2) years. At T1 and T2, ADHD symptoms were assessed with clinical parent interviews and parent and teacher questionnaires. Neurocognitive functions (i.e. T1: inhibitory control, working memory (WM), T2: verbal and performance intelligence (IQ-p)) were assessed using (neuro-)psychological tests. At T1, HCC was analyzed in the most proximal 3 cm scalp hair segment using luminescence immunoassay. RESULTS: Exclusively in boys, low HCC correlated with low WM and IQ-p. The sex-by-HCC interaction effect on WM was significant. In boys, HCC completely explained the links of ADHD inattention symptoms with WM and IQ-p, respectively. CONCLUSION: Results suggest a specific neurocognitive/endocrine profile in preschool boys at risk of developing ADHD, comprising hypocortisolism combined with memory and attention deficits.