Effects of physical activity on cortisol levels in African American toddlers attending full-time daycare

Abstract

Cortisol is a glucocorticoid hormone secreted by the adrenal cortex in response to both physical and psychological stressors. A baseline, diurnal pattern of activity, which peaks soon after waking and declines throughout the day to a low point in the evening, begins to establish itself during infancy. However, research now suggests that cortisol levels are atypical (i.e., elevated during the afternoon) in young toddlers on days when they attend full-time daycare. The implications of long-term elevated cortisol levels on the functioning of the immune system, as well as on cognitive and brain development, appear to be detrimental, so research is warranted to identify interventions that result in positive changes towards more typical cortisol patterning. Exercise has been shown to be related to increased positive affect and lower cortisol levels, and these findings suggest that physical activity may be an option for regulating cortisol response in toddlers attending full-time, center-based daycare. In this study, participants were 22 African American toddlers who attended low-income full-time daycare in Alabama, all of whom were sampled under control and physical play conditions. For both conditions saliva samples were collected at 9:45 a.m., 10:35 a.m., 11:30 a.m., and 3:30 p.m., and the outdoor physical play treatment session was conducted at 10:00 a.m. Actiheart™ heart rate monitors and video analysis were used to monitor the children’s engagement in the physical play. The saliva sample was collected using a Sorbette, without stimulant. Results showed a significant lowering of mean cortisol levels at mid-afternoon on days with physical play in the morning when compared to the control days. No change in cortisol levels was seen pre- to post-physical activity as had been expected, however a significant increase was observed between the 10:35 a.m. and 11:30 a.m. samples under both conditions. Heart rates were significantly higher during the play condition in comparison to the control condition, but only a weak to moderate relationship was found between higher heart rate during the physical play and lower cortisol mid-afternoon. Future research is needed to better understand the influence that physical activity may have on the hypothalamic-pituitary-adrenocortical stress cascade in young children.