What it measures.
Cortisol is the primary glucocorticoid released in response to stress, following a strong circadian rhythm with levels peaking 30-45 minutes after waking and declining throughout the day. While essential for energy and stress response, chronic elevation suppresses testosterone, disrupts sleep, and promotes central adiposity.
The concentration of cortisol in blood (or saliva). Morning cortisol reflects HPA axis function, while 4-point testing reveals the complete diurnal pattern.
Why it matters.
Cortisol regulates energy metabolism, immune function, and stress response. Chronically elevated cortisol accelerates aging, impairs cognition, suppresses immunity, and promotes visceral fat. Flattened diurnal rhythm indicates HPA axis dysfunction.
Physiology.
The hypothalamic-pituitary-adrenal (HPA) axis regulates cortisol release. CRH from hypothalamus stimulates ACTH from pituitary, which triggers cortisol release from adrenal cortex. Cortisol peaks between 7-9 AM (cortisol awakening response) and reaches its nadir around midnight.
Testing & preparation.
How to prepare
- Test between 7-9 AM for morning cortisol
- Avoid intense exercise 24 hours before
- Note any steroid medications
- Salivary testing available for home collection
When to test
When assessing adrenal function, fatigue, or stress-related symptoms. 4-point salivary testing maps the full diurnal curve.
How often
As needed based on symptoms; follow-up 3-6 months after interventions.
Interpretation.
High cortisol
Common causes:
- Chronic psychological stress
- Cushing's syndrome (rare)
- Excessive steroid medication
- Depression and anxiety disorders
- Sleep deprivation
Implications:
- Suppressed testosterone and thyroid function
- Increased visceral fat storage
- Impaired immune function
- Bone loss, muscle wasting
- Cognitive dysfunction, mood changes
- Accelerated biological aging
Low cortisol
Common causes:
- Adrenal insufficiency
- HPA axis suppression from chronic stress
- Long-term steroid use withdrawal
- Pituitary dysfunction
Implications:
- Fatigue, especially with stress
- Low blood pressure, dizziness
- Poor stress tolerance
- Hypoglycemia
- May indicate 'adrenal fatigue' pattern
Optimization.
Diet
- Stable blood sugar (avoid glucose spikes)
- Adequate protein and healthy fats
- Limit caffeine, especially afternoon
- Avoid alcohol (disrupts cortisol rhythm)
Lifestyle
- Daily stress management (meditation, breathing exercises)
- Regular moderate exercise (intense training elevates cortisol)
- Quality sleep 7-9 hours
- Morning sunlight exposure to support circadian rhythm
- Time in nature reduces cortisol
Supplements
- Ashwagandha (evidence for cortisol reduction)
- Phosphatidylserine
- Magnesium for stress resilience
- Adaptogenic herbs (rhodiola, holy basil)
FAQs.
What's the difference between blood and saliva cortisol testing?
Blood cortisol measures total cortisol (free + protein-bound). Saliva measures only free cortisol (the biologically active 1-3%). Saliva testing is non-invasive and allows easy collection at multiple time points to map the full diurnal curve. Late-night salivary cortisol is the recommended first-line screening for Cushing's syndrome. Blood testing with ACTH stimulation remains gold standard for diagnosing adrenal insufficiency.
Is 'adrenal fatigue' a real condition?
Conventional medicine doesn't recognize 'adrenal fatigue' as a diagnosis, as the adrenals don't simply 'tire out.' However, HPA axis dysregulation from chronic stress is well-documented—characterized by blunted morning cortisol response and flattened diurnal curve. This pattern can cause fatigue, poor stress tolerance, and various symptoms. Addressing chronic stress, improving sleep, and supporting the HPA axis through lifestyle interventions can help restore normal function.