There are exceptions to this.
Sleep is one of this Back Page scribe’s favourite recurring topics.
One previous stab at this column concerned the cortisol awakening response, the stress-chemical jolt that supposedly kicks you out of bed in the morning.
Now a new paper published by none other than the Proceedings of the Royal Society B begs to differ with that entire concept.
The Back Page is currently house- and cat-sitting and has been sleeping poorly on account of both the unaccustomed house and cat.
This morning, for example, I woke in the dark to the disconcerting clacking and scrabbling noise of what turned out to be the cat dragging her favourite toy down the timber staircase.
I woke again later, but still in the dark, with said cat standing on the mattress next to my face with her tiny snout in my glass of water.
When I was at last legitimately woken by the alarm chiming on my phone, I’m not sure if it was technically stress I felt but it wasn’t pleasant.
Changes detected after wakening, usually in saliva, have been interpreted as a cortisol spike in response to the stressor of waking, the authors from Bristol University write – “a distinct phenomenon superimposed upon the circadian rhythm of cortisol and an ancient adaptive feature preparing the body in anticipation of the energy needs for the day ahead”.
CAR is now an accepted concept among psychoneuroendocrinologists (yikes) and commonly used as a biomarker of stress reactivity and functionality of the hypothalamic-pituitary-adrenal axis, with variations in CAR reported for Cushing’s, chronic fatigue, depression, psychosis, PTSD and obesity.
The flaw in all this, the authors point out, is that it’s hard to test someone’s spit while they’re asleep to properly measure the change.
The Bristol team instead analysed data collected as part of the Dynamic Hormone Diagnostics (ULTRADIAN) observational cohort study, which used portable microdialysis to continuously sample subcutaneous tissue for each of 214 participants over 72 hours.
While cortisol increased with time in the hour before waking there was no difference upon or in the hour after waking. Individuals also varied substantially, with some experiencing a decrease in the hour before waking.
Not a great or reliable biomarker of much, then.
A close look at previous studies supporting the existence of CAR finds they have used “surprise” early forced awakenings, which the present authors note can in themselves be stressful.
It is not noted whether cats played any role in these studies, but the Back Page is willing to bet they would have found a fair bit of cortisol in my spit had they sampled it during the toy episode.
Send ear plugs and story tips to penny@medicalrepublic.com.au.
