Date Published: April 3, 2019
Publisher: Public Library of Science
Author(s): Jerrald L. Rector, Louis Tay, Christopher W. Wiese, Elliot M. Friedman, Igor Branchi.
Regulation of cortisol under resting conditions is widely used to assess physical and psychological status, but due to the diversity of possible assessments (e.g., cumulative levels; diurnal patterns), considering one or a few at a time hampers understanding and interpretation. Moreover, most studies of cortisol regulation focus on negatively-valanced experiences. This study examined the inter-correlations among cortisol indices and their relative contribution to the explained variance in diverse psychosocial and health factors, including positive functioning.
Data are from midlife and older adults (N = 513; 47.2% male). Cortisol was assessed in urine (overnight) and saliva (at rest and over 4 consecutive days). Positive and negative psychosocial and health factors were assessed by self-report. In addition to examining associations among cortisol indices, relative weight analysis was used to determine which indices were most robustly linked to specific psychosocial factors.
Inter-correlations among indices were weak-to-moderate, suggesting that they measure different aspects of hypothalamic-pituitary-axis activity. Overall variance in psychosocial and health factors (R2) explained by the cortisol indices ranged from 0.01 to 0.07. Of this explained variance, relative weight analysis showed that waking cortisol contributed most to the variance in hedonic well-being (32.1%–38.2%), bedtime cortisol to depression-related factors (32.1%–46.9%), the cortisol awakening response to eudaimonic well-being (35.8%–50.5%), cortisol slope to perceived stress (29.2%), and urinary cortisol to physical factors (38.5% and 62.7%).
Positive and negative factors were related to largely non-overlapping cortisol indices. This study illuminates nuanced associations among cortisol indices and diverse aspects of mental and physical health, facilitating thoughtful examination of the complex role of hypothalamic-pituitary-axis activity in health.
Resting and non-stress cortisol levels have been assessed in different tissues (e.g., saliva, urine, blood) and over different time scales (e.g., momentary, change across the day, accumulation over many hours) . While not all assessments are thought to tap into the same aspects of hypothalamic-pituitary-adrenal (HPA) regulation (e.g., the cortisol awakening response (CAR) is distinct from other diurnal cortisol measures; ), the extent to which they converge or diverge from one another is unclear because few studies include multiple cortisol indices within the same individuals. Similarly, few studies have examined multiple cortisol indices simultaneously to determine which among them is most robustly associated with specific aspects of mental or physical health. Thus, it is also unclear whether these indices have overlapping or distinct relationships with psychosocial factors, and further, if unique associations differ in magnitude relative to one another. Finally, the majority studies examining links between HPA function and psychosocial factors have focused on negatively-valenced experiences, such as distress and depression [3–5], leaving open the question of potential links to positive psychosocial functioning [6–8].
Table 2 shows descriptive statistics for the outcome variables and their zero-order correlations with the cortisol measures. Participants were on average 55 years old and 47% male. The average level of education was less than a 4-year degree. On average, participants reported that paying their bills was not very difficult, and most were overweight.
The current study examined the relationships among commonly used cortisol indices under resting and non-stress conditions, as well as the relative importance of these indices in explaining the variance of positive and negative psychosocial and physical health factors. The results showed largely weak-to-moderate correlations among indices, adding to prior evidence that different assessments of HPA function under non-stress conditions are separate and have distinct interpretations [2, 10–13]. In the same vein, relative weight analysis showed different cortisol indices were related to measures of mental and physical health in distinct ways. Below, these results are examined in the context of the broader literature, highlighting some potential implications.