Feeding-Induced Cortisol Response in Newborn Infants

Context: Understanding the biological rhythms and stress response in sick newborns is important to minimize the negative effects of intensive care. Salivary cortisol has been used as a noninvasive surrogate marker of adrenal function; however, understanding of its control variables is insufficient. Objective: To investigate the presence of feeding-induced cortisol response and its control variables in newborns. Design, Setting, and Patients: Fifty-three newborn infants, who were between 30 and 40 weeks' corrected age and were on 3-hourly regular oral/enteral feeding, were recruited between January 2013 and June 2014. Main Outcome Measure: Saliva samples were collected before and 1 hour after regular feeding. Dependence of cortisol levels (adjusted for postnatal age) and their feeding-related elevation on clinical variables was assessed by using generalized estimating equations. Results: Higher cortisol levels were associated with corrected age ≥37 weeks and saliva samples collected after feeding (both P < 0.001). Oral feeding was associated with a greater feeding-induced cortisol response compared with exclusive enteral feeding (P = 0.034), whereas a prolonged feeding duration (≥30 minutes) was associated with a reduced cortisol response compared with brief feeding (<30 minutes) (P < 0.001). Gestational age, corrected age, antenatal/postnatal glucocorticoids, type of milk, and daily feeding volume had no effect on cortisol response. Conclusions: Feeding-induced cortisol response was observed in newborns. The cortisol response was more prominent following oral feeding and was reduced with prolonged feeding. Future studies may investigate whether feeding-induced cortisol response plays a role in the acquisition of adrenal ultradian and diurnal rhythms.