Do children in daycare have elevated cortisol levels?

Question

An article named Children's elevated cortisol levels at daycare is used to argue against daycare.

Our main finding was that at daycare children display higher cortisol levels compared to the home setting. [...] We speculate that children in center daycare show elevated cortisol levels because of their stressful interactions in a group setting.

Answer 1

Two brand-new, publicly accessible review articles confirm that this study had a sampling bias. It's basically children from low-risk, middle-class white backgrounds that exhibit higher cortisol levels in day care. Children from other backgrounds may have positive results, depending on the quality of care.

Child Care and Cortisol Across Infancy and Toddlerhood: Poverty, Peers, and Developmental Timing (2016)

For children from high-risk contexts, within-child increases in child care hours were predictive of cortisol decreases. The inverse was evident for children from low-risk contexts. This relation grew across toddlerhood. Whereas a history of greater center-based child care was predictive of heightened cortisol levels for low-risk families, this was not the case for children from high-risk families. Irrespective of risk, greater peer exposure (between children) was associated with lower cortisol levels.

A review of research on the effects of Early Childhood Education and Care (ECEC) upon child development (2015)

A recent review of the largest and most representative childcare studies in the US and many smaller studies concluded that the effects of quantity of care on children’s behaviour problems were population specific: for disadvantaged children and those from minority ethnic families, extensive childcare was not associated with more externalizing problems – in some cases it predicted lower levels, possibly compensating for other disadvantages (Huston et al., 2015).