Objectives: Cortisol levels have been related to mood disorders at the group level, but not much is known about how cortisol relates to affective states within individuals over time. We examined the temporal dynamics of cortisol and affective states in depressed and non-depressed individuals in daily life. Specifically, we addressed the direction and timing of the effects, as well as individual differences.
Methods: Thirty depressed and non-depressed participants (aged 20-50 years) filled out questionnaires regarding their affect and sampled saliva three times a day for 30 days in their natural environment. They were pair-matched on age, gender, smoking behavior and body mass index. The multivariate time series (T=90) of every participant were analyzed using vector autoregressive (VAR) modeling to assess lagged effects of cortisol on affect, and vice versa. Contemporaneous effects were assessed using the residuals of the VAR models. Impulse response function analysis was used to examine the timing of effects.
Results: For 29 out of 30 participants, a VAR model could be constructed. A significant relationship between cortisol and positive or negative affect was found for the majority of the participants, but the direction, sign, and timing of the relationship varied among individuals.
Conclusion: This approach proves to be a valuable addition to traditional group designs, because our results showed that daily life fluctuations in cortisol can influence affective states, and vice versa, but not in all individuals and in varying ways. Future studies may examine whether these individual differences relate to susceptibility for or progression of mood disorders. (C) 2016 Elsevier Ltd. All rights reserved.