The cortisol awakening response in toddlers and young children.

The cortisol awakening response (CAR) is frequently assessed in psychoneuroendocrinological research on adult participants. However, knowledge on the development of the CAR during early life is scarce and characterized by inconsistent findings. We have recently shown that a positive CAR is readily observable in young infants under conditions of strict methodological control. However, it still remains unknown whether a significant CAR is maintained consistently throughout toddler- and childhood. Here, we report data from 150 toddlers and young children aged 12-87 months in whom salivary cortisol levels were assessed 0 and 30 min post-awakening over three non-consecutive study days. High quality of data was ensured by the use of objective measures to verify children's awakening times (wrist actigraphy) and sampling times (electronic monitoring containers). Results revealed the presence of a significant CAR (>1.5 nmol/L) in 142 (out of 150) children and on a total of 82% of study days. A marked CAR was consistently observed throughout all examined age groups (mean increase: 8.73 nmol/L). In addition, the level of cortisol on awakening was found to increase linearly with children's age (r=.17, p=.04). Overall, the current findings strongly suggest that, contrary to previous propositions, the CAR is maintained consistently throughout toddler- and childhood.