In plain language
What it is
The body's stress-hormone system that sets cortisol and your daily energy rhythm.
Why it matters
In long COVID it looks mis-tuned, with a flattened cortisol rhythm that fits fatigue.
Think of it like
A thermostat for stress and morning alertness that has drifted off its setting.
For specialists
Formal definition
The hypothalamic-pituitary-adrenal axis regulating cortisol; long COVID shows low morning cortisol without compensatory ACTH and a flattened diurnal rhythm.
Mechanism
Central (hypothalamic-pituitary) dysregulation rather than primary adrenal failure is implicated.
Sources
- Salivary cortisol: flattened diurnal rhythm in long COVID free full text ›