Cortisol Detection Methods and the Hormone's Role in Evaluating Circadian Rhythm Disruption

Cortisol follows a 24 h circadian rhythm that plays a pivotal role in maintaining the optimal function of various physiological systems in alignment with behavioural cycles. Its synthesis and secretion are regulated by the hypothalamic-pituitary-adrenal (HPA) axis. The 24 h fluctuations of cortisol may result from physiological changes influencing its regulation, or conversely, hormone-mediating physiological changes within the body. This review mainly aims to synthesize current evidence on methods for detecting cortisol. In addition, it focuses on evaluating cortisol's potential as a biomarker for circadian disruption and related health impacts. A literature search was conducted across databases, including Google Scholar, PubMed, and Scopus, using search terms such as "circadian rhythm OR circadian clock OR circadian disruption OR circadian dysregulation" and "cortisol OR hydrocort* OR corticoid OR corticosteroid". A total of 47 articles were included on methods of cortisol detection, and 41 articles were reviewed for their health implications. Cortisol measured via saliva, blood serum, urine, interstitial fluid (ISF), and sweat has been reported as suitable for 24 h monitoring, reflecting circadian regulation. In contrast, hair cortisol is suitable for identifying chronic changes and prolonged elevations in cortisol levels. This review highlights the stability, suitability, and challenges of each detection method, including reported cortisol levels across studies. Additionally, it provides a comprehensive overview of health implications associated with changes in cortisol, offering insights into its potential as a marker for circadian disruption and related health outcomes.