Cortisol changes at awakening are mainly driven by the body's natural circadian rhythm of the hormone.

Awakening not associated with an increased rate of cortisol secretion
Go to source) For many years it has been generally accepted that waking up results in a stimulus to release hormone cortisol - a phenomenon called the “cortisol awakening response” (CAR). This response has been used to investigate many clinical conditions including PTSD, depression, obesity, and chronic fatigue syndrome (ME/CFS).
‘Spike in #stresshormones you feel after #waking? It's likely NOT caused by waking itself, but the natural peak of #cortisol production that occurs shortly after your usual wake-up time. #sleep’

A major limitation of studies using CAR is that protocols typically only assess samples obtained after waking up, and not in the period prior to this, since measurements are taken in saliva. Consequently, the studies are not able to prove a change in the rate of cortisol secretion over the awakening period. 




To resolve the critical question of whether the rate of cortisol secretion actually increases after wakening, the Bristol research team used an automated sampling system to measure tissue cortisol levels both before and after wakening in 201 healthy male and female participants aged between 18 to 68 years old. The researchers found awakening did NOT result in an increase in cortisol release, with no evidence for a change in the rate of cortisol increase in the hour after waking when compared with the hour prior to waking.
Cortisol Dynamics: More Than Just the First Hour
Importantly, the study also observed substantial interindividual variability in absolute concentration and rate of change, and differences in dynamics that may be attributed to length and timing of sleep. Based on these findings, the researchers suggest caution is needed when interpreting cortisol measurements solely obtained in the hour after waking.Furthermore, the results also suggest that if cortisol has any relationship to awakening, it is with factors that contribute to the initiation of awakening rather than being a response to it.
Circadian rhythms, the natural 24-hour cycles of physiological and behavioural patterns, are extremely important adaptations to living on our planet with its daily light:dark and temperature oscillations, and disturbances of these rhythms contribute to many psychological, metabolic, cardiovascular and immunological health conditions. Understanding the role of cortisol rhythms in many of these conditions will be very important for researchers understanding of these disorders and their potential treatment.
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Dr Thomas Upton, Clinical Research Fellow and co-lead author in the Bristol Medical School: (THS), explained: “By measuring both before and after waking, this study provides much needed and crucial insight into the dynamics of cortisol with respect to sleep and endogenous rhythms. For me, a key message is that much caution should be exercised if attempting to interpret post-wake cortisol values where information about the pre-waking state is not known.”
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“Making sure our work is robust and reproducible – including rigorously testing previous findings – is a central part of the research culture we try to foster at the University of Bristol.”
The research team suggest that future studies on mechanisms of arousal from sleep both overnight and during the morning should carefully consider dynamic changes in the activity of the hypothalamic pituitary axis - the system in the body that regulates the stress response and the release of cortisol – in addition to sleep and behaviour.
Reference:
- Awakening not associated with an increased rate of cortisol secretion - (https://royalsocietypublishing.org/doi/10.1098/rspb.2024.1844)