Covariation in Salivary Cortisol and IL-6: Within-Person Associations are Time Dependent

Abstract

In acute stressor paradigms, salivary cortisol is inversely associated with salivary inflammation interleukin(IL)-6, but in daily life the association between cortisol and cytokines are likely complex. The present investigation examined stable between-person and dynamic within-person associations between salivary cortisol and salivary IL-6 in daily life. Twenty-four healthy couples (n=24 males and n=24 females) provided saliva samples 4x per day (waking, mid-morning, afternoon, bedtime) for 5 days, which were assayed for cortisol and IL-6. Separate multilevel models for men and women that controlled for diurnal rhythm, age, and BMI were used to test the between- and within-person (concurrent and lagged) associations between salivary cortisol and IL-6. Between people, cortisol was negatively but not significantly associated with IL-6 in men and women (men: γ=-0.50, p=0.255; women: γ=-1.30, p=0.073). Within people, salivary cortisol and IL-6 were not concurrently associated in men (γ=-0.35, p=0.11) or women (γ=-0.15, p=0.395), but there were significant and positive within-person lagged effects: in men, when lagged by two time points (γ=0.41, p=0.015), and in women (γ=0.42, p=0.009) when lagged by one time point. When women (and men) had higher cortisol at the previous time point (or two time points before), they had higher IL-6 levels. Although cortisol typically inhibits inflammation, this effect may be more evident at the between-person level. Our results suggest that the association between cortisol and IL-6 within-person may vary temporally when measures are localized in the oral cavity.