Cortisol awakening response in infants during the first six postnatal months and its relation to birth outcome.

CONTEXT The rise of cortisol concentrations after awakening is well documented in adults and children and commonly used as easily accessible marker of hypothalamic-pituitary-adrenal (HPA) reactivity. OBJECTIVE The purpose of this study was to demonstrate the existence of a salivary cortisol awakening response (CAR) in infants, and to estimate its association with birth outcome. SETTING The study was conducted in the general community. PARTICIPANTS Healthy infants up to six months age (N=64). MAIN OUTCOME MEASURES Mothers were instructed to collect their infant's saliva immediately and 30 min after awakening on two days within 45 days, irrespective of awakening time. Information on birth outcome was collected from medical records and questionnaires. RESULTS Linear mixed models analysis revealed a significant rise of infant salivary cortisol concentrations within 30 min after awakening (b=0.128, SE=0.024, t61=5.31, p<0.001), which was quite stable across the two sampling days (r=0.40, p=0.002). The infant CAR was predicted by length of gestation (t58=2.44, p=0.018). CONCLUSIONS The current data demonstrate the existence of a CAR in infants as early as during the first six postnatal months; its relationship with length of gestation supports its usefulness for questions related to developmental neuroscience. Therefore, the infant CAR emerges as non-invasive biomarker of HPA axis dynamics at this early stage of life, with relevance for future research and potential clinical applications.