University of Bristol Study Reveals Cortisol Rise Happens Before Waking, Not After

University of Bristol Study Reveals Cortisol Rise Happens Before Waking, Not After

(IN BRIEF) A new study from the University of Bristol has challenged the long-standing belief that waking up triggers a spike in cortisol, the body’s stress hormone. Published in Proceedings of the Royal Society B, the research shows that cortisol begins to rise before waking, as part of the body’s natural preparation for the day, and does not significantly increase immediately after waking. By measuring cortisol levels both before and after awakening in 201 participants, the study found no significant change in the rate of cortisol secretion post-wake, suggesting that changes in cortisol are more linked to the body’s circadian rhythm. The study calls for more careful interpretation of cortisol data, particularly when it is measured only after waking.

(PRESS RELEASE) BRISTOL, 15-Jan-2025 — /EuropaWire/ — A groundbreaking study led by the University of Bristol has debunked the long-held belief that waking up triggers a surge in cortisol, the body’s primary stress hormone. Contrary to the widely accepted idea of a “cortisol awakening response” (CAR), which has been used to study conditions such as PTSD, depression, and chronic fatigue syndrome, the research found that cortisol levels do not significantly increase immediately after waking. Instead, the hormone begins rising several hours before waking, as part of the body’s natural preparation for the day ahead.

The study, published in Proceedings of the Royal Society B on January 15, 2025, challenges existing protocols that typically only measure cortisol levels after waking. The research team, led by Professor Stafford Lightman at Bristol’s Medical School, utilized an innovative automated sampling system to assess cortisol levels both before and after awakening in 201 healthy participants, aged 18 to 68 years. Their findings show no substantial change in cortisol levels during the hour after waking compared to the hour before, suggesting that any changes observed immediately post-wake are likely the tail end of the body’s circadian rhythm.

The research also noted considerable individual differences in cortisol levels and changes, with factors such as sleep duration and timing influencing these variations. The study highlights the importance of considering the full dynamics of cortisol secretion, rather than relying solely on post-wake measurements, which could lead to misinterpretation of data.

Professor Lightman emphasized that the study offers a fresh perspective on how cortisol interacts with sleep and awakening. “Our findings open a new framework for understanding how cortisol rhythms may be disrupted in conditions like sleep disorders and depression,” he said. Dr. Thomas Upton, co-lead author, reinforced the importance of measuring cortisol dynamics both before and after waking to gain a fuller understanding of its relationship to sleep. Professor Marcus Munafò also underscored how this study challenges established scientific beliefs, calling for a more rigorous approach to testing long-standing findings.

The research was funded by the EU Horizon 2020 ‘Ultradian’ grant and the Biotechnology and Biological Sciences Research Council (BBSRC).

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SOURCE: University of Bristol