Associations between biological stress markers and depression are inconsistent across studies. We assessed whether inter- and intra-individual variability explain these inconsistencies. Pair-matched depressed and non-depressed participants (N = 30) collected saliva thrice a day for 30 days, resulting in 90 measurements per individual. The relationships between measures of stress-system function and depression were examined at the group level by means of mixed model analyses, and at the individual level by means of pair-matched comparisons. The analyses were repeated after adjusting for time-varying lifestyle factors by means of time-series regression analyses.

Project: Mood and Movement in Daily life. The primary aim of this study is to investigate the role of physical activity in the etiology of depressed mood, individual differences therein, and clues for tailor-made interventions. A second aim of this study is to elucidate the temporal relationship between mood symptoms and several stress-related hormones and enzymes, such as cortisol and alpha-amylase.