Waking up does not activate an increase in the release of the stress hormone cortisol, according to new research led by the University of Bristol. The study, published in the Proceedings of the Royal Society B on January 15th, challenges the long-standing assumption that waking up triggers a spike in cortisol levels.
For years, the cortisol awakening response (CAR) has been used to study various clinical conditions like PTSD, depression, obesity, and chronic fatigue syndrome. However, previous studies only measured cortisol levels after waking up, overlooking the period leading up to awakening. This new research aimed to fill this gap by monitoring cortisol levels before and after waking in a group of 201 healthy participants.
Surprisingly, the study found no evidence of an increase in cortisol release upon waking. Instead, cortisol levels appeared to follow a natural daily rhythm, starting to rise in the early hours of the morning and peaking shortly after the participants’ habitual wake time. This suggests that any changes in cortisol levels immediately after waking are likely part of the body’s circadian rhythm rather than a direct response to waking up.
The study also revealed significant variability in cortisol levels and dynamics among individuals, which could be influenced by factors like sleep duration and timing. These findings emphasize the importance of considering individual differences when interpreting cortisol measurements taken around waking.
Professor Stafford Lightman from Bristol Medical School highlighted the implications of the study, stating that it provides a new framework for understanding the relationship between cortisol, sleep, and various health conditions. Dr. Thomas Upton, a co-lead author of the study, emphasized the need for caution when interpreting post-wake cortisol values without knowledge of the pre-waking state.
The research team’s findings shed light on the role of cortisol in circadian rhythms and its potential impact on sleep disorders and other health conditions. Moving forward, they suggest that future studies should consider the dynamic changes in the body’s stress response system during both overnight sleep and awakening.
In conclusion, this research challenges previous assumptions about the cortisol awakening response and highlights the complexity of cortisol dynamics in relation to waking up. By reevaluating established beliefs, the study contributes to a deeper understanding of the body’s natural rhythms and their impact on health and well-being.
