Introduction: Amassing evidence suggests that post-awakening salivary cortisol rhythms (changes in cortisol throughout the day) may indicate health status. We previously established summary parameters for salivary cortisol in U.S. Navy Sea, Air, and Land and reported excellent parameter stability across 2 days of repeated sampling. To confirm the generalizability of our original findings to other military populations, we replicated the procedures of our prior report in another specialized military group. The purpose of this study was to (1) establish summary parameters of daily salivary cortisol rhythms, (2) evaluate summary parameter stability, and (3) assess the impact of sampling compliance in U.S. Navy Explosive Ordnance Disposal (EOD) technicians.
Materials and methods: Seventy active duty, male Explosive Ordnance Disposal technicians (mean ± SD age; 34.9 ± 6.5 years) self-collected saliva samples in a nondeployed setting on two consecutive weekdays at WAKE, WAKE + 30 min, WAKE + 60 min, 4 p.m., and 9 p.m. For salivary cortisol, we computed summary parameters, i.e., measures of magnitude and measures of pattern, and then evaluated their stabilities via correlational analyses and Cronbach's alpha (α). Compliance was objectively and subjectively evaluated using actigraphy and self-reported data, respectively. This research was conducted under a Naval Health Research Center Institutional Review Board approved study (NHRC.2015.0013).
Results: Average salivary cortisol concentrations increased at WAKE + 30 (mean ± SE reactivity; 48.9 + 6.8%) from WAKE, followed by a swift recovery at WAKE + 60. Approximately 10.9% of the group were classified as negative-responders (i.e., < 0% change from WAKE to WAKE + 30). The measures of magnitude demonstrated fair stability across two days (r value range: 0.37-0.45, ps < 0.01; α range: 0.54-0.62). Fifty-five percent of the sample was classified as compliant (defined as <15 min deviation from target sampling times) across both days. Compliance decreased to 31% when compliance criteria were refined to <5 min deviation; however, controlling for compliance did not overwhelmingly influence the more stable summary parameters of magnitude.
Conclusions: These findings demonstrate a thorough replication, with some additional refinement, of our prior study, implying generalizability across diverse military populations. Study limitations include unsupervised saliva collection in a free-living setting, which is counterbalanced by ecological validity. The noninvasive salivary sampling protocol used in this study yields stable estimations of daily cortisol rhythms in specialized military men and is recommended as an operational health surveillance tool by which to monitor chronically stressed military members.
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