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Chronic stress and elevated cortisol are associated with adverse metabolic profiles and lifestyle patterns, systemic low-grade inflammation, and increased chronic disease risk; however, it is less clear how the degree of cortisol fluctuations impacts these parameters. Adult men and women (18-70y) were recruited to participate in a 5-day observational study, in which they underwent a baseline health and body composition assessment, completed 5-day diet, exercise, and stress records, and provided saliva samples in the morning, afternoon, and evening to measure fluctuations in cortisol, interleukin-1β (IL-1β), and IL-6. Degree of cortisol variability over the 5-day period (highest cortisol measure - lowest cortisol measure) was used to classify subjects into high (n = 9) and low (n = 9) cortisol fluctuation groups. Participants with greater fluctuations in salivary cortisol had higher salivary cortisol concentrations on average, which was attributed to higher maximal and morning cortisol. A greater proportion of individuals with higher cortisol flux worked in first responder/emergency professions, and exhibited minimal dietary pattern differences compared to those with low cortisol flux. While body fat percentage and mass positively correlated with minimum salivary cortisol measures, body composition and blood pressure did not differ between low vs. high salivary cortisol flux groups. Interestingly, we observed diurnal patterns of salivary IL-1β concentrations, with higher IL-1β in the morning, and greater afternoon IL-1β in the high cortisol flux group compared to the low cortisol flux group. Independent of cortisol flux, waking satiety and intake patterns of dietary nutrients and food groups/type differentially correlated with salivary cytokine concentrations in a time of day-dependent manner. Our findings suggest that greater fluctuations in cortisol are associated with distinct diurnal salivary cortisol and IL-1β concentrations but minimal lifestyle and dietary factors, whereas dietary patterns are strongly and differentially associated with salivary cytokine profiles.

Using salivary inflammatory markers as a noninvasive biomonitoring technique within natural social contexts has become increasingly important to link social and biological responses. Many studies have associated circulating cytokines to distinct aspects of physical activity and social/emotional behavior; however, they have not been linked to success and failure in a naturalistic setting for military personnel performing tasks. In this study, salivary cytokines were studied in a group of fifteen Air Force Reserve Officers’ Training Corps (ROTC; 14 males, 1 female) subjects performing three mock hostage rescue missions, designed to prompt responses associated with baseline, success, and failure. Each subject completed the tasks of the mission individually and again in randomly assigned teams. Participants were outfitted via direct skin contact with comfortable external Zephyr™ sensors to monitor heart rate, breathing rate, and activity while completing each task. Saliva samples were collected before and after the completion of each mission, and cytokine levels were quantified using enzyme-labelled immunoassay (ELISA) beads. These biomarkers were used to describe the body’s immune response to success and failure when performing a mock rescue mission individually and in a team. All measured cytokine levels increased following failed missions performed individually, compared to cytokine levels associated with successful missions. When completing the tasks as a team, there were no significant differences in cytokine response between success and failure; however, being in a team stimulated an increased pre-mission cytokine response, suggesting the concept of teamwork and performing with peers for the first time had a more significant impact than the notion of failing. Additionally, none of the cytokines tested for individual missions correlated to physical activity markers (heart rate, breathing rate, activity) measured during performance. These results indicate a potentially new noninvasive method of determining social stress levels under taxing conditions.

Salivary markers of immune function are increasingly commonly used in studies of human health. Yet, few studies have examined the short-term or long-term reliability or stability of these biomarkers, making their measurement properties unclear. We addressed this issue in the present study by collecting two saliva samples, two hours apart, from 426 adolescent girls during a baseline laboratory visit. Then, eighteen months later, we collected the same samples again from a subset of these participants (n = 113). The correlations between the two samples collected at each session were generally high (mean r = 0.67). In contrast, although single saliva samples were only weakly correlated across 18 month (mean rs = 0.18), averaging the two quantifications within a session considerably improved the reliability (mean r = 0.27). In short, salivary immune markers exhibited strong short-term test-retest correlations, and averaging across multiple assessments notably improved long-term test-retest correlations. Additional research is needed to establish the health relevance and mechanisms underlying these potentially useful, non-invasive biomarkers., (Copyright © 2019 Elsevier Inc. All rights reserved.)