Comprehensive integrative analysis of circadian rhythms in human saliva

The circadian clock orchestrates vital physiological functions, with its dysregulation implicated in various pathologies. Assessing human clock status via the measurement of circadian rhythms is crucial for health management and disease treatment. Saliva provides a non-invasive means for such analysis. In this study, we examined circadian rhythms and related parameters in 21 healthy individuals (n = 4 - 19 per experiment), assessing different data types, including saliva gene expression with our TimeTeller^® methodology, hormone levels, cell composition, and self-assessment tests for chronotype evaluation. While substantial individual variability of the circadian profiles was observed, we found significant correlations between the acrophases of ARNTL1 gene expression and of cortisol, and both acrophases correlated with the bedtime of individuals on the sampling day. Our findings validate the robustness and reliability of our method for determining peripheral clock circadian rhythms in humans, offering potential for clinical applications in diverse cohorts.