Research paper
Bowles NP, Thosar SS, Butler MP, Clemons NA, Robinson LD, Ordaz OH, Herzig MX, McHill AW, Rice SPM, Emens J, Shea SA. The circadian system modulates the cortisol awakening response in humans. Frontiers in Neuroscience. 2022;16:995452.
Why we cite it
Complements `ccy01` (a narrative review) with direct human laboratory evidence, and does so from an open-access source we can fully verify. Its key contribution to the corpus is demonstrating that the cortisol rhythm is endogenous — driven by the circadian system rather than merely by the act of sleeping and waking — and that the awakening response is gated by circadian phase: largest when waking falls about three hours before habitual wake time, and effectively absent when someone wakes at a circadian phase corresponding to the afternoon or evening.
It also supplies the corpus with the honest limits on that finding, which a narrative review does not: the rhythm is a group-level result that roughly a third of individual participants did not show, its amplitude varied more than twofold between the two samples, and the total sample is 35 adults.
DOI: 10.3389/fnins.2022.995452 · PubMed 36408390 · Publisher