Interactions of momentary thought content and subjective stress predict cortisol fluctuations in a daily life experience sampling study

Daily life stress is an omnipresent phenomenon in modern society. Research has linked prolonged activation of the hypothalamic-pituitary-adrenal axis to psychiatric and somatic diseases. Everyday stressors substantially contribute to these health risks. Despite the notion that the physiological stress response is highly dependent on concurrent psychological processes, investigations associating diurnal cortisol levels with subjective experience have primarily focused on affective states. The impact of everyday cognitive processes including thought content has been largely neglected. To investigate this link, moment-to-moment associations of psychological experience including subjective stress, thought content and affect, and cortisol levels were assessed throughout the daily routines of 289 healthy adult participants. We found that subjective stress interacted with current thought content and affect in predicting cortisol release: more negative and future-directed thoughts were associated with higher cortisol levels after experiencing subjective stress, suggesting an increase in negative future anticipation. Concurrent cortisol rises might reflect proactive coping to adequately prepare for upcoming demands. In the absence of subjective stress, more past-directed thoughts and negative affect were associated with higher cortisol levels. These findings provide evidence for a fundamental link between thought content and daily cortisol activation, and highlight the significant contribution of thought patterns to physiological stress levels.


Supplementary statistical analysis
Exploratory analyses. To assess frequencies of specific thought patterns, the three-dimensional cube of thought was divided into subfields most closely resembling thought clusters of rumination (negative, self-and past-directed thought) and worry (negative, self-and futuredirected thought). These subfields constituted thoughts that combined scores in the outmost half of a respective pole (e.g., negative pole) of the respective thought dimensions (e.g., valence dimension).

Effects of stressor characteristics on cortisol levels in samples with reports of subjective stress.
To assess the association of both the stress magnitude and the success of coping with the stressor with cortisol levels, the following model (Model 2) was derived from the main model and fit to a conditional subsample of the dataset (i.e., all samples reporting subjective stress): Level 1: Ysdi = π0di + π 1di (time) + π 2di (stress magnitude) + π 3di (stress coping) + π4di (stress magnitude*stress coping) + etdi Level 2: π 0di = β00i + β 02i (awakening time) + u0di Level 3: β00i = γ000 + γ001 (sex) + r00i Effects of closeness of one's company on cortisol levels. For those samples in which participants reported being in company of others, the association of cortisol levels with the closeness of one's company was assessed with the following model (Model 3): Level 1: Ysdi = π0di + π 1di (time) + π 2di (closeness) + etdi Level 2: π 0di = β00i + β 02i (awakening time) + u0di Level 3: β00i = γ000 + γ001 (sex) + r00i Lag analysis. To explore the association between reports of stress in a current sample with reports of stress in the following sample, we used a Pearson's Chi-squared test with Yates' continuity correction for a 2x2 table with the current and lagged report of subjective stress as variables of interest.

Supplementary results
Descriptive analysis of reported activities revealed a wide range of sampled activities throughout the daily routines of participants. Most frequently, these activities were work-related (>58%), followed by being on the computer/online (14.8%), commuting (7.8%), and relaxing or resting (4.9%).
Analysis of frequencies of thought clusters (operationalized as subfields of the threedimensional cube of thought) revealed 10 cases (0.2%) of potentially ruminative thought content (marked by the conjunction of pronounced negative, self-and past-directed content) and 23 cases (0.4%) of potentially worrysome thought content (marked by the conjunction of pronounced negative, self-and future-directed content). Table S1 shows the results for Model 2. In those samples which reported subjective stress, neither the magnitude of the stressor (p > .9) nor the coping success (p > .7) or their interaction (p > .8) were related to cortisol levels. Table S2 shows the results for Model 3. In those cases in which participants reported being in company of others, the closeness they felt toward this company was not significantly associated with cortisol levels (p = 0.214).
Pearson's Chi-squared test revealed that the likelihood of reporting stress in a sample significantly differed depending on whether stress was reported in the previous sample.
Reporting stress was more likely when having reported stress in the previous sample (43%) as opposed to reporting stress when not having reported stress in the previous sample (13,3%), χ² (1, N = 2222) = 207.1, p < 0.001; odds ratio = 4.93.