Cortisol
Cortisol is the body's primary stress hormone, produced by the adrenal glands in response to signals from the hypothalamus and pituitary (HPA axis). It follows a diurnal rhythm: highest in the early morning (6–8 AM) to promote wakefulness, declining throughout the day, and lowest around midnight.
Cortisol plays essential roles in glucose metabolism, blood pressure regulation, immune function, and inflammation control. Chronic elevation (from persistent stress, sleep deprivation, or overtraining) is associated with abdominal fat accumulation, muscle breakdown, immune suppression, impaired memory, and metabolic dysfunction.
Morning cortisol is the most commonly measured timepoint. Because of cortisol's diurnal rhythm, the time of blood draw significantly affects interpretation. A morning cortisol below 10 mcg/dL may warrant further investigation for adrenal insufficiency, while levels consistently above 20 mcg/dL (morning) may suggest Cushing's syndrome or chronic stress.
What It Measures
Serum cortisol measures the total cortisol in the blood at the time of the draw. It includes both protein-bound and free cortisol. Results must be interpreted in context of the time of day.
Reference Ranges
| Status | Range (mcg/dL) |
|---|---|
| Optimal | 10–15 mcg/dL (morning) |
| Normal | 6–18 mcg/dL (morning) |
| Borderline | 18–23 mcg/dL (morning) |
| Out of Range | > 23 mcg/dL or < 5 mcg/dL (morning) |
Optimal Ranges
| Group | Range | Unit | Source |
|---|---|---|---|
| AM (6–8 AM) | 6.2–19.4 | ug/dL | Standard reference |
| PM (4 PM) | 2.3–11.9 | ug/dL | Standard reference |
| Optimal AM | 10–18 | ug/dL | Functional range |
When Values Are High
Chronically elevated cortisol (Cushing's pattern) causes weight gain (especially visceral), muscle wasting, bone loss, immune suppression, insulin resistance, and cognitive impairment.
When Values Are Low
Low cortisol (Addison's or adrenal insufficiency) causes fatigue, hypotension, salt cravings, darkened skin, and inability to handle stress. "Adrenal fatigue" is controversial but HPA axis dysfunction is recognized.
What To Do
Lifestyle
- •Morning sunlight exposure helps set cortisol rhythm
- •Regular moderate exercise (not overtraining)
- •Meditation/breathwork lowers cortisol 15–25%
- •Consistent sleep-wake schedule supports circadian cortisol
Supplements
- •Ashwagandha (300–600mg) reduces cortisol by ~15–25% in clinical trials
- •Phosphatidylserine (400mg) may blunt exercise-induced cortisol spikes
- •Magnesium glycinate supports HPA axis regulation
When to Retest
Always test AM cortisol (before 9 AM, fasting); 4-point salivary cortisol for full diurnal pattern
How GATOR Tracks This
Lab Providers
Related Biomarkers
This content is for informational purposes only and does not constitute medical advice. Reference ranges may vary by laboratory and individual factors. Consult a qualified healthcare provider for interpretation of your results and treatment decisions.
Track Cortisol in GATOR
Import your lab results and see how this biomarker trends over time with AI-powered context.
Get Started Free