The present study evaluated relations between life stress exposure and hypothalamic pituitary adrenal (HPA) axis functioning, indicated by salivary cortisol levels. Prior research on HPA axis functioning under conditions of significant life stress exposure among children has been inconclusive. Inconsistencies in prior research were thought to be partially attributable to the influences of several moderating variables. In particular, children's trauma exposure, perceptions of the impact of stressors, depressive symptoms, and posttraumatic stress symptoms were hypothesized to moderate relations between life stress exposure and cortisol levels. Age was positively associated with both A.M. and P.M. cortisol levels. Life stress exposure was positively associated with P.M. cortisol levels. However, this relation was moderated by posttraumatic stress symptoms. In circumstances of low life stress exposure, children with higher posttraumatic stress symptoms exhibited higher P.M. cortisol levels than children with lower symptoms. As exposure to life stress increased, P.M. cortisol increased among children with lower posttraumatic stress symptoms, but remained the same among children with higher. In addition, recurrent trauma exposure contributed to decreased A.M. cortisol levels and increased P.M. cortisol levels. These findings were also illustrated in an exploratory cluster analysis, which revealed three distinct patterns of cortisol levels, each of which were associated with a specific levels of life stress exposure, trauma exposure, and posttraumatic stress symptoms. Results suggest that associations between stress exposure and basal cortisol levels are influenced by complex interactions among development, frequency of life stressors, frequency and duration of traumatic events, and posttraumatic stress symptoms
