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 on 15 January in the Proceedings of the Royal Society B, challenges the long-standing assumption that waking up triggers a spike in cortisol levels.
For years, the cortisol awakening response (CAR) has been used as a marker to investigate various clinical conditions such as PTSD, depression, obesity, and chronic fatigue syndrome. However, previous studies have only focused on cortisol levels after waking up, neglecting the period leading up to awakening. To address this gap, the Bristol research team employed an automated sampling system to measure tissue cortisol levels before and after waking in over 200 healthy participants.
Surprisingly, the researchers found that awakening did not result in an increase in cortisol release. There was no significant change in the rate of cortisol secretion in the hour after waking compared to the hour before waking. This suggests that any fluctuations in cortisol levels upon waking are more likely tied to the body’s natural cortisol rhythm, which peaks shortly after habitual wake time.
The study also highlighted significant variability in cortisol levels among individuals, influenced by factors like sleep duration and timing. These findings underscore the importance of considering the entire cortisol rhythm, rather than focusing solely on post-awakening levels, when interpreting cortisol measurements.
Furthermore, the research sheds light on the intricate relationship between cortisol rhythms and various health conditions. Disruptions in circadian rhythms, the body’s internal clock, can contribute to a range of health issues including psychological, metabolic, cardiovascular, and immunological disorders. Understanding how cortisol dynamics interact with these conditions is crucial for developing effective treatments.
Professor Stafford Lightman from Bristol Medical School emphasized the study’s implications for understanding the link between cortisol, sleep, and health conditions. Dr. Thomas Upton, a co-lead author of the study, cautioned against interpreting post-wake cortisol values without considering the pre-waking state. Professor Marcus Munafò highlighted the importance of rigorous research practices in challenging established beliefs and fostering a culture of reproducibility.
Moving forward, the research team suggests that future studies on sleep arousal mechanisms should consider the dynamic changes in the hypothalamic-pituitary axis, the system regulating the stress response and cortisol release. By taking a comprehensive approach to studying cortisol dynamics, researchers can gain valuable insights into the complex interplay between sleep, stress, and health.
In conclusion, the study’s findings challenge conventional wisdom about cortisol awakening response and offer a new perspective on the intricate relationship between cortisol rhythms and health. By unraveling the mysteries of cortisol dynamics, researchers are paving the way for innovative approaches to managing various health conditions.
