Longitudinal associations between salivary cortisol to C-reactive protein ratios and psychological well-being in Chinese adults

Abstract

Background Salivary C-reactive protein (CRP) could be a viable biomarker of inflammation and has been associated with stress outcomes. The hypothalamic–pituitary–adrenal axis can modulate stress-related inflammation. This study aimed to evaluate the interaction effects of immune–endocrine markers on psychological outcomes. Methods The study participants were 52 healthy Chinese adults who collected 10 saliva samples over 2 consecutive days at baseline. The participants completed validated measures on anxiety, depression, positive affect, and sleep disturbance at baseline and 1 month later. The stability and diurnal patterns of salivary cortisol and CRP were investigated via paired t-tests and repeated-measures analyses of variance. Regression analysis was used to examine the longitudinal associations between immune–endocrine markers and their interactions (cortisol [Cort]: morning CRP [CRPmorn] and Cort:CRPeven) and psychological measures. Results Salivary cortisol and CRP displayed satisfactory stability over 2 consecutive days and diurnal patterns of abrupt and gradual decline during the day, respectively. Controlling for baseline psychological measures and confounding variables, Cortmorn and diurnal cortisol slope was significantly and negatively associated with anxiety symptoms and positive affect 1 month later, respectively. Cort:CRPeven and Cort:CRPmorn was significantly and positively associated with depressive symptoms and sleep disturbance 1 month later, respectively. Conclusion These findings offer initial support for the prognostic utility of salivary cortisol and CRP and their balance as determinants of psychological health in healthy adults.