Cortisol
Adrenal stress hormone with a central role in metabolism
Also known as
Definition
Cortisol is the primary glucocorticoid of the adrenal cortex, regulated by pituitary ACTH (HPA axis). It follows a pronounced circadian rhythm (morning peak, evening trough). Cortisol mobilizes energy reserves (gluconeogenesis), dampens inflammation, modulates the immune system, and influences memory, sleep, and mood. Chronically elevated levels are associated with metabolic syndrome, immune suppression, and bone loss.
| Parameter | Value |
|---|---|
| Unit | nmol/l (µg/dl) |
| Reference Range | Morning (8 am): 170–550 nmol/l (6–20 µg/dl) | Evening (8 pm): 55–250 nmol/l (2–9 µg/dl) |
Agree on your personal target range with your doctor.
Conversion: 1 µg/dl = 27.6 nmol/l. US labs: morning value 6–23 µg/dl, evening value < 5 µg/dl.
↓ What a low value means
Low cortisol values (< 170 nmol/l in the morning) can indicate adrenal insufficiency (primary: Addison's disease; secondary: pituitary insufficiency) or HPA axis suppression from exogenous corticosteroids. Symptoms: exhaustion, weight loss, hypoglycemia, hypotension, hyponatremia, darkened skin pigmentation (primary).
↑ What a high value means
Chronically elevated cortisol indicates Cushing's syndrome (endogenous: ACTH-producing tumor; exogenous: corticosteroid medications), chronic stress, or severe psychiatric illness. Consequences: central obesity, hyperglycemia, osteoporosis, muscle wasting, immune suppression, hypertension, depression.
✓ What can influence this value
Cortisol follows a daily rhythm with the highest value in the morning and is influenced by time of day, sleep duration and sleep quality, physical and psychological stress, and exercise (intense strain and overtraining can raise the value). Caffeine, estrogen preparations (which raise total cortisol), glucocorticoid medications, diseases of the adrenal gland or pituitary, and shift work also act on the value. Results are only well comparable when the sample is taken at the same time of day.
When to test
In the morning, between 7 and 9 am, for a baseline value. For suspected Cushing's: low-dose dexamethasone suppression test. Salivary cortisol day profile (4 measurements) is better than a single blood measurement for HPA axis assessment. 24-hour urinary free cortisol reflects total daily output.
Frequently asked questions
What is the Cortisol Awakening Response (CAR)? +
In the first 30–45 minutes after waking, cortisol physiologically rises by 50–160% — this is the Cortisol Awakening Response (CAR). A pronounced CAR indicates healthy HPA axis reactivity. A flat CAR (no response) is associated with chronic stress, burnout, and HPA axis exhaustion.
Can 'adrenal fatigue' be detected by blood test? +
The popular concept of 'adrenal fatigue' is not medically recognized and cannot be detected by standard blood tests. True adrenal insufficiency (Addison's disease) is rare and diagnosed through specific tests (stimulation test, ACTH test). Fatigue symptoms should be thoroughly investigated.
How does sleep deprivation affect cortisol? +
Sleep deprivation (< 6 hours) elevates evening levels and blunts the physiological cortisol decline, disrupting the circadian rhythm. Chronic sleep deprivation leads to elevated daytime cortisol, insulin resistance, and immune suppression. Regular sleep schedules are the most effective measure for normalization.
How does chronic stress affect the immune system through cortisol? +
Acute stress and short-term elevated cortisol are physiological and can temporarily activate the immune system. Chronically high cortisol suppresses the immune system by inhibiting Th1 cells, NK cells, and pro-inflammatory cytokines — leading to increased infection susceptibility and slower wound healing.
Cortisol
Sources
- Chrousos GP (2009) Stress and disorders of the stress system. Nat Rev Endocrinol.
- Nicolaides NC et al. (2010) Stress, the stress system and the role of glucocorticoids. Neuroimmunomodulation.
- Cay M et al. (2018) Effect of increase in cortisol level due to stress in healthy young individuals on dynamic and static balance scores. North Clin Istanb.
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.