Biphasic glucocorticoid rhythm in one month old infants

CONTEXT: The hypothalamus-pituitary-adrenal (HPA) axis displays a diurnal rhythm. However, little is known about its development in early life.

OBJECTIVE: To describe HPA-axis activity and study possible influencing factors in 1-month-old infants.

DESIGN: Observational.

SETTING: Amsterdam UMC, location VUMC, and OLVG, Amsterdam.

INTERVENTIONS: Collection of breastmilk and infants’ saliva 1 month postpartum for analysis of glucocorticoids (GCs; i.e., cortisol and cortisone) using LC-MS/MS.

RESULTS: A significant biphasic GC rhythm was detected in infants, with peaks at 6:53±1:01 (mean±SEM) and 18:36±1:49 for cortisol, and at 8:50±1:11 and 19:57±1:13 for cortisone. HADS-score, POP-consultation, season at sampling and sex were not associated with the infants’ GC rhythm. Breastmilk cortisol maximum was positively associated with infants’ cortisol area-under-the-curve (AUC) increase and maximum. Higher breastmilk cortisone AUCincrease, AUCground and maximum were associated with an earlier maximum in infants. Breastmilk and infant GC concentrations were associated between 6:00-9:00.

CONCLUSIONS: A biphasic GC rhythm, peaking in the morning and evening, was seen in 1-month-old infants at a group level. Breastmilk GC parameters might be associated with the infants’ GC rhythm, possibly caused by a signaling effect of breastmilk GCs, or as an associative effect of increased mother-infant synchrony. These results contribute to an increased understanding of early-life HPA-axis development.