Infant hair cortisol: associations with salivary cortisol and environmental context

Abstract

Early chronic stress has enduring implications for physical and mental health outcomes. Hair cortisol concentration (HCC) has emerged as a marker of cumulative cortisol exposure, yet HCC in infants is not well understood. We examined how infant HCC relates to widely used basal salivary cortisol measures, maternal HCC, and environmental context in 111 infants assessed at 6 and 12 months of age. Maternal HCC at 6 and 12 months was correlated with infant HCC at 12 months. At 12 months, infant HCC was positively associated with waking salivary cortisol concentration (SCC), evening SCC, and area under the curve (AUC), but was independent of diurnal slope. Breastfeeding was associated with lower HCC, whereas increased sleep disruption was related to flatter slope. Reduced nighttime sleep duration was related both to higher HCC and to flatter slope. A person-focused analysis indicated that the combination of high HCC and flattened slope was associated with more environmental risks, highlighting the importance of investigating the interplay between HCC and diurnal cortisol slope. Results support the validity of HCC as a marker of cumulative cortisol exposure in infancy, while emphasizing the value of including multiple cortisol measures assessing distinct aspects of hypothalamic-pituitary-adrenal (HPA) function.

Keywords: breastfeeding; diurnal cortisol; hair cortisol; infancy; sleep; socioeconomic status.

© 2016 Wiley Periodicals, Inc.

Figures

Figure 1.

Slope across the day by sleep duration classification Note. Y-axis indicates SCC value after winsorizing and log transformation. Standardized SCC values were not used in order to make it easier to interpret the slope across the day. X-axis indicates the SCC sample time, showing the decline in basal SCC across the day.

Figure 2.

Socioeconomic status (a) and sleep disruption (b) by infant cortisol profile. Note. The Y-axis indicates mean standardized SES score (2a) and mean standardized sleep disruption score (2b) for each infant cortisol profile. The X-axis represents all four infant cortisol profiles. Standard errors are indicated by the error bars.

Figure 3.

Breastfeeding status (a) and sleep duration status (b) by infant cortisol profile. Note. The Y-axis indicates number of infants the X-axis represents all four infant cortisol profiles.