Salivary Cortisol as a Biomarker of Sleep Quality: A Scoping Review

Abstract

Background: Sleep is a crucial regulator for physiological and psychological balance, and sleep disturbances have been associated with the hypothalamic–pituitary–adrenal (HPA) axis. Cortisol exhibits a circadian rhythm and plays a central role in stress response and metabolic regulation. Salivary cortisol has been widely used as a non-invasive biomarker for sleep quality, but its reflection remains unclear. This scoping review aims to systematically map and evaluate the existing literature on the relationship between salivary cortisol and sleep outcomes. Methods: Medline, Scopus, and Cochrane databases were applied to identify relevant studies. Database searches combined specific terms from three concept groups: cortisol, sleep quality, and biomarkers. This protocol follows the JBI guidelines. To be incorporated, records pertaining to any type of study design that mentions the use of salivary cortisol and the analysis of sleep quality were considered. Finally, 1067 studies were imported. Among those, 31 studies met eligibility criteria and were extracted. Result: The results indicated the trend in the use of salivary cortisol as a sleep quality biomarker; the study shows limited consistency as a biomarker. Its relationship with sleep outcomes is highly dependent on methodological factors and contextual influences. Conclusions: Overall, salivary cortisol may reflect broader stress-related physiological processes rather than sleep quality directly.

The authors' abstract, as published at the source. Clocks & Sleep, 2026 · DOI ↗