Morning cortisol: adrenal steroid with a strong daily rhythm.
What it is
Serum cortisol in nmol/L. Morning samples (typically 08:00–09:00) are preferred. Afternoon values are naturally lower.
Cortisol from the adrenal cortex follows a circadian rhythm: highest in the early morning, lowest at night. Serum morning cortisol is a screening snapshot; diagnosing adrenal excess or deficiency usually needs dynamic tests.
Why it matters
Abnormal cortisol testing for Addison’s or Cushing’s follows specialist protocols (including dynamic tests), not a single DIY reading. Steroid creams, oestrogen, and shift work affect interpretation.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Cortisol mobilises glucose, modulates immunity, and helps blood pressure under stress. Chronic excess or deficiency both harm tissues widely.
Cortisol raises glucose availability, modulates immunity, and supports vascular tone under stress. Chronic excess harms bone, skin, mood, and metabolism; deficiency can be life-threatening in crisis.
For athletes
Athletes love “adrenal fatigue” myths, that is not a recognised medical diagnosis. True adrenal insufficiency is serious and needs endocrinology. Overreaching can alter diurnal rhythms; use validated sports-medicine pathways, not supplement stacks from social media.
“Adrenal fatigue” is not a recognised diagnosis. Overreaching alters sleep and perceived stress; restore load and fueling with qualified support. Suspected true adrenal disease needs urgent proper medicine, not supplement stacks.
