DAMPENING OF THE CORTISOL RESPONSE TO HANDLING AT 3 MONTHS IN HUMAN INFANTS AND ITS RELATION TO SLEEP, CIRCADIAN CORTISOL ACTIVITY, AND BEHAVIORAL DISTRESS

The decrease in responsiveness of the hypothalamic-pituitary-adrenocor tical (HPA) system is marked over the fir st months of life. Seventy-e ight healthy infants (44 girls), 7 to 15 weeks old, were given a labor atory mock physical examination. Salivary cortisol samples were collec ted pre- and postexamination and at home. Behavioral state during the examination and home sleep/wake activity were measured. Subjects young er than 11 weeks showed art increase in pre- to postexamination cortis ol, while older subjects did not. Further, there was no decrease in be havioral distress to the examination with age. Infants who showed an e arly- morning peak (EMP) in home cortisol levels were significantly ol der and were likely to be those who slept through the night. However, the presence of an EMP-was not associated with a lack of cortisol resp onse to the examination. The decrease in cortisol responsiveness witne ssed around the age of 3 months is presumably due to other processes a ssociated with age, and not with the expression of the day-night rhyth m in basal cortisol. (C) 1998 John Wiley & Sons, Inc.