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

Abstract

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. 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. 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. 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. 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.