Do depressive symptoms mediate the relationship between hopelessness and diurnal cortisol rhythm?

BACKGROUND Research has revealed a well-established relationship of depressive symptoms and hopelessness with a variety of physical illnesses that are associated with a dysfunction of the hypothalamic-pituitary-adrenal-axis. PURPOSE The purpose of this study was to test if depressive symptoms mediate the relationship between hopelessness and cortisol, a measure of the hypothalamic-pituitary-adrenal-axis. METHODS Hopelessness, depressive symptoms, and diurnal cortisol rhythm were measured in 257 adults (128 women and 129 men; age range, 20-74 years) in this cross-sectional study. To test the hypothesis, two linear regression analyses and asymmetrical confidence intervals around the regression weights were conducted. A second set of analyses was calculated to be able to exclude the possibility of hopelessness as a mediator between depressive symptoms and cortisol. RESULTS As predicted, after adjusting for age, gender, awakening time, and medication use, more hopelessness predicted more depressive symptoms and more depressive symptoms predicted a flatter diurnal cortisol rhythm. The 95% confidence intervals revealed that the indirect relationship between hopelessness and diurnal cortisol rhythm was significant. The analyses with hopelessness as a potential mediator revealed that hopelessness does not mediate the association between depressive symptoms and cortisol. CONCLUSIONS While the relationship between hopelessness and cortisol was mediated by depressive symptoms in this cross-sectional study, many other risk factors of depression have not been examined. Thus, future longitudinal studies should examine the relationships between those risk factors of depression and the hypothalamic-pituitary-adrenal-axis.