The stress hormone cortisol is not activated when waking up in the morning, a new study has suggested.
Instead, cortisol is activated in the hours before we wake up in order to prepare us for the day ahead, researchers from the University of Bristol have revealed.
Previously, it was believed that waking up can trigger the development of cortisol known as the ‘cortisol awakening response’ (CAR).
During the study, the team of researchers analysed the tissue cortisol levels of 201 adults both before and after awakening.
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They discovered that cortisol levels did not increase for an hour after people awakened in the morning.
Any changes in cortisol around the time of waking up are caused by the initiation of awakening rather than being a response to it.
Circadian rhythms are the physical, mental, and behavioural changes that occur in a 24-hour cycle. They are regulated by the brain’s internal clock and are influenced by light and dark.
Disrupting circadian rhythms can trigger the development of several cardiovascular, psychological, metabolic and immunological health conditions.
First author Professor Stafford Lightman said: “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.”
Joint author Dr Thomas Upton said: “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.”
Corresponding author Marcus Munafò said: “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.”
Read the full study in the journal Proceedings of the Royal Society.
