The relation between physical activity, family stress, and diurnal cortisol patterns in middle childhood

Cortisol, the primary end product of the hypothalamic pituitary adrenal axis, has been closely linked with health and health behaviors in daily life. Not only physical health, but also familial stressors (i.e. perceived anxiety/stress, economic hardship, parenting styles) have been found to relate to cortisol levels. The present study investigated the complex relation between family level stress and cortisol levels longitudinally, and the extent to which physical activity plays a role in such relations. Specifically, I examined: 1) direct associations between physical activity (sedentary, moderate-to-vigorous activity) and diurnal cortisol slopes a year later, 2) whether physical activity levels mediated established links between family stress and diurnal cortisol slopes, and 3) whether family stress moderated associations between physical activity and diurnal cortisol slopes. Data were from the Arizona Twin Project, a racially and socioeconomically diverse sample of twins in middle childhood in Arizona (N=710; Mageatbaseline=8.44 years, SD=.69; 51.4% female; 58.5% non-Hispanic White, 23.7% Hispanic). Twins and their caregivers participated in a 7-day study (age 8) during which they wore an actigraphy watch to capture physical activity measurements. Primary caregivers also provided self-reports on stressors and mental health. Results revealed a non-significant main effect of physical activity on AM cortisol slopes, as well as non-significant interactions and main effects in the moderating pathways. Mediation analyses were not pursued due to lack of correlation between physical activity and family stress.