Is the cortisol awakening response truly a response to awakening? Replication and extension using overnight sampling.
Level 4 - case-series / case-control
Small observational repeated-measures physiological laboratory study without a control group.
PubMed 39751816 · doi:10.1007/s00421-024-05676-z
What was done
Twelve participants completed two overnight sleep laboratory sessions with blood sampled every 15 minutes via an intravenous catheter from 20:30 h until 1 hour post-awakening, yielding 802 serum samples. Cortisol concentrations were assayed, and piecewise linear mixed-effects models evaluated whether post-awakening cortisol rises deviated significantly from pre-awakening baseline trajectories modeled across varying time windows.
What was found
The post-awakening cortisol rise deviated significantly from the pre-awakening trend only when assuming a simple linear rise beginning 4 hours (beta = 1.79, 95% CI: 0.49 to 3.09, p = 0.007) or 5 hours (beta = 1.79, 95% CI: 0.49 to 3.09, p = 0.007) before waking. When a non-linear trajectory across the 4-hour pre-awakening window was accounted for, the post-awakening deviation lost statistical significance (beta = 0.96, 95% CI: -0.74 to 2.66, p = 0.266).
Why it matters
These findings suggest that the cortisol awakening response may largely reflect an ongoing circadian trajectory rather than an acute, discrete physiological burst triggered solely by the act of waking.
Limits
The sample size was very small (12 participants), limiting statistical power and generalizability. Participant characteristics (age, sex, health status) are not specified in the abstract, and conclusions depend heavily on the mathematical assumptions chosen to model pre-awakening non-linear curves.
Cited by
- context Cortisol levels begin rising approximately 30 minutes before waking up.