New! Sign up for our email newsletter on Substack.

Study Challenges Long-Held Beliefs About Morning Stress

In a finding that challenges decades of scientific assumptions, new research reveals that waking up doesn’t trigger a surge in stress hormones. Instead, your body prepares for the day ahead by gradually increasing these hormones hours before you open your eyes.

The study, published January 15 in the Proceedings of the Royal Society B, overturns the widely accepted notion of a “cortisol awakening response” – the belief that the act of waking triggers the release of the stress hormone cortisol.

Rewriting the Morning Narrative

“Our study opens up a whole new framework for understanding the relationship of overnight increases in cortisol with sleep, and how this may be disrupted in sleep disorders, depression and many other conditions,” explains Stafford Lightman, Professor of Medicine at Bristol Medical School: Translational Health Sciences (THS), and one of the study’s lead authors.

The research team used an automated sampling system to measure cortisol levels in 201 healthy volunteers aged 18 to 68, tracking the hormone both before and after waking – a crucial innovation that previous studies couldn’t achieve.

A More Natural Process

Rather than finding a stress response to waking, the researchers discovered that cortisol levels begin rising in the early hours of the morning as part of the body’s natural preparation for the day ahead. This increase reaches its peak shortly after a person’s usual wake time, suggesting the body anticipates awakening rather than reacting to it.

Implications for Health Research

The findings have significant implications for how researchers study various health conditions. For years, the assumed “cortisol awakening response” has been used to investigate PTSD, depression, obesity, and chronic fatigue syndrome (ME/CFS).

Dr. Thomas Upton, Clinical Research Fellow and co-lead author at Bristol Medical School, emphasizes the need for caution in interpreting morning cortisol measurements: “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.”

Challenging Scientific Assumptions

The study also highlights the importance of questioning established scientific beliefs. Professor Marcus Munafò, Associate Pro Vice-Chancellor – Research Culture at the University of Bristol, notes: “As well as providing important insights into the biology of our sleep-wake cycles, this work illustrates how findings that have become received wisdom within the research community may be wrong.”

Looking Forward

The research team suggests that future studies on sleep and waking should carefully consider changes in the body’s stress response system alongside sleep patterns and behavior. This more comprehensive approach could lead to better understanding of sleep disorders and related health conditions.


Did this article help you?

If you found this piece useful, please consider supporting our work with a small, one-time or monthly donation. Your contribution enables us to continue bringing you accurate, thought-provoking science and medical news that you can trust. Independent reporting takes time, effort, and resources, and your support makes it possible for us to keep exploring the stories that matter to you. Together, we can ensure that important discoveries and developments reach the people who need them most.