Cortisol
Cortisol is the main glucocorticoid hormone in humans. The adrenal glands release it at the end of the hypothalamic-pituitary-adrenal (HPA) axis, a stress-response chain, and it helps regulate metabolic, cardiovascular, immune and behavioral processes.
What it means in practice
Under stress, corticotropin-releasing factor (CRF) starts a chain of signals that ends with glucocorticoids released from the adrenal cortex, the outer layer of the adrenal glands [1]. Along the way, a hormone called ACTH binds a receptor in the adrenal cortex and drives glucocorticoid production [1]. Glucocorticoids then dampen further HPA activity, a feedback loop that limits how much is released and for how long [1].
Studies measure cortisol in blood, urine or saliva [2]. Salivary cortisol is widely used as a marker of psychological stress, but it reflects the HPA axis only indirectly, and saliva levels do not always track blood levels, especially during a stress response [2].
One common measure is the cortisol awakening response: the marked rise in cortisol over the first 30-45 minutes after waking [3]. People usually collect their own saliva samples at home, so the result depends on following a timed schedule that starts at the moment of waking [3]. A 2022 evaluation found little improvement in how studies applied the main recommendations, especially objective checks of sampling times [4].
Why it matters when reading nootropics research
When a supplement trial reports cortisol, it might report a change in morning blood cortisol, or in salivary cortisol after a lab stress test. Before reading much into it, check what was sampled (blood or saliva) and when [2][3], and, for awakening-response studies, whether sampling times were objectively verified [4].
A cortisol change is a marker result. It is not the same as people feeling less stressed, which NootropicsWork reports as a separate outcome, perceived stress.
References
- Smith SM, Vale WW. The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress. Dialogues Clin Neurosci. 2006.
- Hellhammer DH, Wüst S, Kudielka BM. Salivary cortisol as a biomarker in stress research. Psychoneuroendocrinology. 2009.
- Stalder T, Kirschbaum C, Kudielka BM, et al. Assessment of the cortisol awakening response: Expert consensus guidelines. Psychoneuroendocrinology. 2016.
- Stalder T, Lupien SJ, Kudielka BM, et al. Evaluation and update of the expert consensus guidelines for the assessment of the cortisol awakening response (CAR). Psychoneuroendocrinology. 2022.