Cortisol
Also known as: Serum Cortisol
What Does Cortisol Measure?
Cortisol is a steroid hormone produced by the adrenal glands, located just above the kidneys. A cortisol blood test measures the amount of this hormone circulating in your bloodstream at a specific moment in time. Because cortisol follows a strong daily rhythm — peaking in the early morning (around 6–8 AM) and dropping to its lowest levels at night — tests are typically timed to capture either the morning peak or afternoon trough, giving clinicians a snapshot of adrenal gland function.
Why Does Cortisol Matter?
Often called the 'stress hormone,' cortisol plays a central role in regulating metabolism, immune response, blood pressure, and the body's reaction to physical or emotional stress. It helps control blood sugar levels, reduces inflammation, and assists in memory formulation. Chronically elevated or depressed cortisol levels can signal serious underlying conditions such as Cushing's syndrome, Addison's disease, or adrenal tumors, and are also associated with burnout, anxiety, poor sleep, and metabolic dysfunction. Monitoring cortisol is essential for diagnosing adrenal disorders and assessing overall hormonal balance.
Normal Ranges
Males
Morning (6–8 AM): 6–23 mcg/dL (165–635 nmol/L); Afternoon (4 PM): 2–13 mcg/dL (55–358 nmol/L)
Females
Morning (6–8 AM): 6–23 mcg/dL (165–635 nmol/L); Afternoon (4 PM): 2–13 mcg/dL (55–358 nmol/L)
Children
Varies by age; Newborns: 1–24 mcg/dL; Children 1–16 years: 3–21 mcg/dL (morning). Consult pediatric reference ranges.
Causes of High Levels
- Cushing's syndrome or Cushing's disease (excess cortisol production from adrenal or pituitary tumors)
- Chronic psychological or physical stress (activates the hypothalamic-pituitary-adrenal axis)
- Long-term use of corticosteroid medications such as prednisone or dexamethasone
- Obesity, particularly central/abdominal obesity, which is associated with cortisol dysregulation
- Adrenal tumors (adenomas or carcinomas) that independently secrete cortisol
- Severe illness, surgery, trauma, or intense overtraining in athletes
Causes of Low Levels
- Addison's disease (primary adrenal insufficiency where the adrenal glands are damaged and cannot produce enough cortisol)
- Hypopituitarism (the pituitary gland fails to produce enough ACTH to stimulate cortisol production)
How to Improve Your Cortisol
Diet
- Reduce refined sugars and processed carbohydrates, which can spike blood sugar and trigger cortisol release
- Increase intake of magnesium-rich foods such as dark leafy greens, pumpkin seeds, almonds, and dark chocolate to support adrenal function
- Consume adequate protein at each meal (25–35g) to stabilize blood sugar and reduce cortisol fluctuations
- Include omega-3 fatty acids from fatty fish (salmon, mackerel) or flaxseeds to help reduce inflammation and blunt cortisol responses
- Limit caffeine intake, especially after noon, as caffeine directly stimulates cortisol secretion and can disrupt sleep-related cortisol rhythms
Supplements
- Ashwagandha (Withania somnifera): 300–600 mg of root extract daily has been shown in clinical trials to significantly reduce cortisol levels
- Phosphatidylserine: 400–800 mg/day may blunt exercise- and stress-induced cortisol spikes
- Magnesium glycinate or citrate: 200–400 mg/day supports the HPA axis and promotes better sleep, reducing nighttime cortisol
- Rhodiola rosea: 200–600 mg/day as an adaptogenic herb shown to reduce stress-induced cortisol elevation
Related Biomarkers
Frequently Asked Questions
What time of day should I get my cortisol blood test?
Cortisol follows a strong daily rhythm, so timing is critical for accurate results. Most doctors order a morning cortisol test between 6–8 AM, when levels are naturally at their highest. An afternoon test (around 4 PM) may also be ordered to check whether cortisol is declining normally throughout the day. Always follow your doctor's specific instructions for timing, and try to avoid strenuous exercise or significant stress before the test, as these can temporarily raise cortisol levels.
Can stress alone cause abnormally high cortisol levels?
Yes, both acute and chronic psychological stress can raise cortisol levels. Physical stressors like illness, surgery, or intense exercise also spike cortisol. However, cortisol elevated purely by lifestyle stress typically remains within or slightly above the normal reference range. Dramatically elevated levels — especially when combined with physical symptoms like weight gain around the midsection, easy bruising, high blood pressure, and stretch marks — are more suggestive of a medical condition like Cushing's syndrome and warrant further investigation.
What are the symptoms of high cortisol (hypercortisolism)?
Common symptoms of chronically elevated cortisol include weight gain particularly around the abdomen and face (sometimes called a 'moon face'), muscle weakness, thin or fragile skin that bruises easily, purple or pink stretch marks, high blood pressure, elevated blood sugar or type 2 diabetes, irregular menstrual cycles in women, reduced libido, anxiety, depression, and difficulty sleeping. If you experience several of these symptoms together, talk to your doctor about testing for Cushing's syndrome.