Diurnal mood variation in depression: A signal of disturbed circadian function?

Background: Diurnal variation in mood is a prominent symptom of depression, and is typically experienced as positive mood variation (PM-V - mood being worse upon waking and better in the evening). The present study sought to advance understanding of PMV by measuring daily mood variation in non-clinical individuals with varying levels of depressed mood. Based on research into normative variation in mood and evidence that circadian amplitudes may be decreased in depression, it was hypothesised that compared to those with low levels of depression, individuals meeting Centre for Epidemiological Studies-Depression Scale (CES-D) cut-off for probable depression would exhibit an attenuated circadian component in diurnal variation of Positive Affect (PA). Method: Ninety-nine young healthy women (mean age = 21.5, SD = 3.0) living on a normal sleep-wake schedule provided mood reports every two hours between 0800 h and 2200 h for 7 days. Results: The high depression group (CES-D >= 23, n = 22) exhibited a pattern of diurnal variation consistent with PMV (increased PA in the evening relative to the morning). As predicted, evidence was also found that the high depression group was characterized by a decreased circadian component to diurnal variation in PA relative to the low depression group (CES-D < 23, n = 77). Conclusions: It is provisionally concluded that diurnal mood variation in depression can usefully be understood from the perspective of weakened circadian function. Findings are discussed in terms of limitations of the study's naturalistic design and future research avenues identified. (c) 2007 Elsevier B.V. All rights reserved.