Hair Cortisol Concentrations in Children: A Longitudinal Analysis Across Childhood.

Hair cortisol concentration (HCC) reflects long-term cortisol exposure and is commonly used as a biomarker of hypothalamic-pituitary-adrenal axis activity. Although increasingly applied in pediatric populations, developmental changes in HCC and potential sex differences remain unclear. This longitudinal study examined HCC across childhood and the influence of sociodemographic and perinatal factors. A total of 212 mother-child dyads participated. Sociodemographic and perinatal data were collected during pregnancy and postpartum. Offspring HCC (pg/mg) was assessed at birth, 6 months, and annually from 1 to 7 years. HCC decreased with age, with the steepest decline occurring in early childhood and greater stability observed between 4 and 7 years of age. Sex differences emerged only at 3 years, with higher HCC in females. Standardized birth height was negatively associated with newborn HCC; maternal BMI and weight before and during pregnancy were negatively associated with HCC at 1-2 years; and gestational week at delivery was positively associated with HCC at 3 years. Descriptive HCC percentiles were calculated for newborns, at 6 months, and at ages 1-3 years. These findings illustrate the developmental trajectory of HCC across childhood and provide insights into sociodemographic and perinatal factors associated with children's HCC.