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Background: The home environment of offspring of parents with bipolar disorder (OBD) has been characterized by high levels of stress and disorganization, which may impact development of the hypothalamic-pituitary-adrenal (HPA) axis and their subsequent risk for affective disorders. The present study examined the effects of a family-based preventative intervention on the OBD's HPA axis functioning and whether intervention-related changes in the home environment might have driven change in the HPA axis.

Methods: Fifty-five children (6-11 years) were recruited from families having a parent with bipolar disorder (n=26) or families having two parents with no current mental disorders (n=29). Only those families with a parent having bipolar disorder participated in the preventative intervention. Both groups completed assessments at baseline, post-prevention, 3-, and 6-months post-prevention. At each assessment, family organization, control, cohesion, conflict, and expressiveness, in addition to childhood internalizing problems, were measured, and offspring saliva samples were collected across two consecutive days.

Results: Hierarchical Linear Modelling found no significant differences in HPA axis functioning between groups at baseline or across time. Improvements in family organization, however, were associated with elevations in participants' cortisol awakening response (CAR; p =.004) and total daily output (p =.023), and a steepening of their diurnal slope (p =.003) across time. Similar findings were obtained for family cohesion with respect to CAR (p <.001) and, to a lesser degree, diurnal slope (p =.064).

Discussion: HPA axis functioning did not differ between the OBD and healthy controls at baseline or in response to the preventative intervention. However, intervention-related improvements in family organization and, to a lesser degree, cohesion, were associated with adaptive changes in HPA functioning over time.