Cortisol & Sleep Timing
topic
Cortisol follows a circadian pattern that reaches its daily nadir during the first half of the night (facilitating deep sleep) and rises sharply in the hour before natural waking (the cortisol awakening response, CAR) — preparing the body and brain for alertness, mobilizing energy, and activating the immune system. Chronic stress producing elevated nocturnal cortisol disrupts slow-wave sleep, fragments sleep architecture, and produces the characteristic anxiety-driven insomnia of elevated HPA axis activation.
Role
The cortisol-sleep relationship creates one of the most vicious cycles in health: stress elevates nocturnal cortisol, which fragments sleep and reduces deep sleep, which impairs the physiological stress recovery that sleep is supposed to provide, which produces higher baseline stress the following day, which further elevates nocturnal cortisol. Most people in this cycle are treating either the stress or the sleep in isolation, without recognizing that they are the same problem expressed in two different domains — and that addressing either one will improve the other through the same biological mechanism.