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

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.