Known as ‘stress hormone’, cortisol’s levels vary through the day in sync with one’s 24-hour cycle
Cortisol levels may not be rising just on
waking up as previously thought, rather they are already on the rise as the
body gets ready for the day ahead, according to a new research.
Researchers, led by those at the
University of Bristol in the UK, found that cortisol levels increase in the
hours prior to awakening as part of the body’s preparation for the day ahead,
so waking up may not be as “stressful” as previously thought, they said.
Known as the ‘stress hormone’, cortisol’s
levels vary through the day in sync with one’s 24-hour cycle, increasing in
response to stress to help the body manage it.
Waking up after a night’s sleep is
considered to trigger cortisol production and is termed the ‘cortisol awakening
response’—something that has been previously studied in varied contexts,
including Post-Traumatic Stress Disorder, obesity and depression.
However, this study, published in the
journal Proceedings of the Royal Society B: Biological Sciences, suggests that
if cortisol has any relationship with waking up, it is with the factors
contributing to the initiation of awakening rather than being a response to it,
the authors said.
They added that previous studies analysing
the cortisol response have typically assessed saliva samples obtained after
waking up, not in the period prior to this.
Consequently, the studies are not able to
prove a change in the rate of cortisol secretion over the awakening period, the
researchers said.
In this study, the team measured cortisol
levels both before and after waking up in over 200 healthy men and women, aged
18-68 years, using an automated system.
“We found no evidence for a change in the
rate of cortisol increase in the hour after waking when compared with the hour
prior to waking,” the authors wrote.
The result suggested that any change in
cortisol levels right after waking are more likely to be the tail end of the
daily rhythm of cortisol—known to increase in the early morning hours and peak
shortly after one usually wakes up every day, the team said.
They also found that duration and timing
of sleep contributed to differences in the participants’ cortisol levels and
rate of change.
Therefore, the authors urged caution while
interpreting cortisol values taken solely in the hour after waking up.
The findings demonstrated that the major
cause of changes in cortisol levels around the time of waking up are largely related
to the endogenous circadian rhythm of cortisol, which is one’s internal rhythm
of cortisol secretion linked to body clock.
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