MECHANISM ENGINE
What Is Cortisol?
I always thought of cortisol as purely a bad thing, the stress hormone, the one you want less of. Turns out that’s only half right. You need it. It’s the timing and the level that matter, not whether it’s there at all.
The Built-In Kettle
Cortisol works a bit like a kettle that’s meant to switch itself on fresh every morning, roughly half an hour after you wake, giving you the natural lift that gets you moving. That’s normal, healthy, meant to happen. It’s also meant to switch itself off in the evening, simmering down so the body can wind toward sleep. Chronic stress leaves the kettle running all day and half the night, never properly switched off, quietly boiling in the background whether you’re actually under threat or just sat scrolling on the sofa. The body can’t always tell the difference between a genuine emergency and a stressful inbox.
Cortisol is released by the adrenal glands and follows a natural daily rhythm, highest shortly after waking and lowest at night. It mobilises energy, raises blood glucose, and heightens alertness, useful in short bursts. Chronic stress keeps cortisol elevated for longer than intended, which can disrupt sleep, raise blood sugar, and, over time, is linked with increased abdominal fat storage and poorer insulin sensitivity.
NHS and NICE materials on stress describe the normal cortisol awakening response as a healthy pattern, distinct from the sustained elevation seen in chronic stress, which is associated with broader metabolic and sleep disruption.
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Related mechanisms
Educational only, not medical advice. Speak to your GP before changing your fasting pattern, diet, or medication.
What this is based on
NHS and NICE guidance, cross-referenced against Neil’s own NHS blood test record going back to April 2012. See the full timeline and current numbers.