Blunted hypothalamo-pituitary-adrenal axis reactivity is associated with the poor intelligence performance in children with attention-deficit/hyperactivity disorder.

The aim of the present study was to examine the effects of hypothalamo-pituitary-adrenal (HPA) axis reactivity on intelligence test performance in subjects with attention-deficit/hyperactivity disorder (ADHD). We investigated the extent to which an increase or decrease in cortisol after stress was associated with the intelligence test performance in 68 clinic-referred children with ADHD. The mean age of the participants was 8.8 years; 54 of the 68 participants were boys and 14 were girls. ADHD was diagnosed using the Kiddie-Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version (K-SADS-PL). Psychological tests, including the Wechsler Intelligence Scale for Children-III and the ADHD diagnostic system (ADS), were administered as a stressor. A saliva sample was collected from each subject before and after psychological testing in order to measure the level of cortisol in the saliva. The cortisol level was measured using a solid-phase radioimmunoassay. Fifty-one of the 68 subjects showed no increase in the level of cortisol after the test. Decreases in the level of cortisol after the test were correlated with poor intelligence performance and the decrease of cortisol in respect to baseline significantly affected the verbal, performance and total IQ (effect sizes, 7.4-9.5%) in subjects who showed blunted responses to stress.