Cortisol is the stress hormone produced by adrenal glands that raises blood glucose by stimulating gluconeogenesis, increases insulin resistance, and promotes visceral fat accumulation. Chronic cortisol elevation worsens diabetes through multiple mechanisms. Cortisol testing methods: morning blood draw (8 AM; reflects peak cortisol; normal 6-20 mcg/dL), 24-hour urinary free cortisol (total daily production; normal less than 50 mcg/24 hours), late-night salivary cortisol (at-home test; should be very low at bedtime; elevation suggests Cushing’s), dexamethasone suppression test (healthy adults suppress own cortisol; failure suggests Cushing’s), and ACTH test (distinguishes pituitary vs adrenal causes). Causes of elevated cortisol: chronic stress, corticosteroid medications (prednisone, dexamethasone — most common overall), Cushing’s syndrome (1 in 100,000+ endogenous cases but underdiagnosed), severe depression. Cushing’s syndrome causes: pituitary tumor (Cushing’s disease, 80% of endogenous), adrenal tumor, ectopic ACTH (lung tumor), or long-term corticosteroid medication use. Cushing’s features: weight gain (abdomen, face “moon face,” upper back “buffalo hump”), thin skin, purple stretch marks, muscle weakness, hypertension, diabetes (50% develop), depression. Adults with treatment-resistant diabetes and Cushingoid features warrant testing. Chronic stress effects: higher fasting glucose, worsened insulin resistance, increased abdominal fat, higher A1C, poor adherence. Cortisol-lowering interventions: regular exercise, adequate sleep, mindfulness, deep breathing, social connection, treating depression if present.
Cortisol Testing Methods
| Test | When/How | Normal Range | Best For |
|---|---|---|---|
| Morning blood cortisol | 8 AM blood draw | 6-20 mcg/dL | Baseline screening |
| 24-hour urine free cortisol | Collect all urine for 24 hours | under 50 mcg/24 hours | Cushing’s screening |
| Late-night salivary cortisol | 11 PM saliva sample at home | under 0.09 mcg/dL | Cushing’s screening |
| 1 mg dexamethasone suppression | Take dexamethasone 11 PM; draw 8 AM | Cortisol under 1.8 mcg/dL | Cushing’s screening |
| ACTH | Blood draw with cortisol | 10-50 pg/mL morning | Distinguish causes |
| CRH stimulation test | Inject CRH; measure ACTH response | Specialized test | Cushing’s evaluation |
Cortisol and Diabetes Connection
- Cortisol stimulates gluconeogenesis (glucose production in liver).
- Cortisol increases insulin resistance.
- Cortisol promotes visceral fat accumulation.
- Cortisol decreases peripheral glucose uptake.
- Cortisol slows wound healing.
- Cortisol increases appetite (especially for high-carb foods).
- Cortisol disrupts sleep, indirectly worsening glucose control.
- Chronic elevation: gradual worsening of diabetes.
- Cushing’s: dramatic glucose elevation; diabetes develops in 50% of cases.
Cushing’s Syndrome Features
- Weight gain — central obesity, “moon face,” “buffalo hump.”
- Thin, fragile skin that bruises easily.
- Purple/red stretch marks (striae) over abdomen, thighs.
- Muscle weakness, especially proximal (climbing stairs, rising from chair).
- Hypertension.
- Diabetes (50% of cases).
- Depression and mood changes.
- Menstrual irregularities.
- Erectile dysfunction in men.
- Osteoporosis.
- Slow wound healing.
- Excess hair growth in women (hirsutism).
- Acne and oily skin.
- Dorsocervical fat pad (“buffalo hump”).
Causes of Elevated Cortisol
- Exogenous (most common): long-term corticosteroid medications (prednisone, dexamethasone).
- Cushing’s disease: pituitary adenoma producing excess ACTH.
- Adrenal tumor: directly producing cortisol.
- Ectopic ACTH: lung or other tumor producing ACTH.
- Chronic stress: modest persistent elevation.
- Severe depression: pseudo-Cushing’s pattern.
- Alcoholism: pseudo-Cushing’s.
- Polycystic ovary syndrome: modest elevation.
Low Cortisol (Adrenal Insufficiency)
- Primary adrenal insufficiency (Addison’s disease) — adrenal gland failure.
- Secondary adrenal insufficiency — pituitary dysfunction.
- Sudden corticosteroid withdrawal.
- Symptoms: fatigue, weakness, weight loss, low blood pressure, skin darkening (Addison’s).
- Life-threatening adrenal crisis: vomiting, dehydration, low blood pressure, low blood sugar.
- Treatment: hydrocortisone replacement.
- Rare but important to recognize.
Stress Management for Cortisol
- Regular exercise — but not excessive (excessive raises cortisol).
- Adequate sleep (7-9 hours).
- Mindfulness meditation — reduces cortisol.
- Deep breathing exercises.
- Time in nature.
- Social connection.
- Therapy for chronic stress or anxiety.
- Limit caffeine — can elevate cortisol.
- Address sleep apnea if present.
- Treat depression if present.
- Yoga and tai chi — cortisol-lowering effects.
When to Test Cortisol
- Difficult-to-control diabetes despite adherence.
- Cushingoid features (weight gain pattern, striae, thin skin).
- Unexplained hypertension.
- Easy bruising.
- Muscle weakness.
- Mood changes.
- Long-term corticosteroid use (assess HPA axis).
- Symptoms of adrenal insufficiency (fatigue, low BP, weight loss).
- Pituitary tumor evaluation.
- Adrenal mass found on imaging.
The Bottom Line
Cortisol is the stress hormone produced by adrenal glands that raises blood glucose by stimulating gluconeogenesis, increases insulin resistance, and promotes visceral fat accumulation. Chronic cortisol elevation worsens diabetes through multiple mechanisms. Cortisol testing methods include morning blood draw (8 AM; normal 6-20 mcg/dL), 24-hour urinary free cortisol (normal less than 50 mcg/24 hours), late-night salivary cortisol (at-home test; should be very low at bedtime), 1 mg dexamethasone suppression test (failure to suppress suggests Cushing’s), and ACTH test (distinguishes causes). Causes of elevated cortisol: chronic stress, corticosteroid medications (prednisone — most common overall), Cushing’s syndrome (1 in 100,000+ endogenous cases but underdiagnosed), severe depression. Cushing’s syndrome causes: pituitary tumor (Cushing’s disease, 80% of endogenous), adrenal tumor, ectopic ACTH (lung tumor), or long-term corticosteroid medication use. Cushing’s features: weight gain (abdomen, face “moon face,” upper back “buffalo hump”), thin skin with easy bruising, purple stretch marks (striae), muscle weakness, hypertension, diabetes (50% develop), depression, menstrual irregularities, osteoporosis. Adults with treatment-resistant diabetes and Cushingoid features warrant testing — especially if features cluster together. Two of three first-line tests (24-h urine, late-night saliva, dexamethasone suppression) confirm Cushing’s diagnosis. Cortisol and diabetes: cortisol stimulates gluconeogenesis, increases insulin resistance, promotes visceral fat, decreases peripheral glucose uptake, slows wound healing, increases appetite for high-carb foods, disrupts sleep. Chronic stress effects on diabetes: higher fasting glucose, worsened insulin resistance, increased abdominal fat, higher A1C, poor adherence. Cortisol-lowering interventions: regular exercise (but not excessive), adequate sleep (7-9 hours), mindfulness meditation, deep breathing, time in nature, social connection, therapy for chronic stress, yoga and tai chi, limit caffeine, treat sleep apnea and depression if present. Low cortisol (adrenal insufficiency, Addison’s disease) is rare but life-threatening — symptoms include fatigue, weakness, weight loss, low blood pressure, skin darkening. Treatment with hydrocortisone replacement. When to test cortisol: difficult-to-control diabetes, Cushingoid features, unexplained hypertension, easy bruising, muscle weakness, long-term corticosteroid use, symptoms of adrenal insufficiency, pituitary or adrenal mass found on imaging. For adults with type 2 diabetes, cortisol evaluation is appropriate when diabetes control is unexpectedly poor or Cushingoid features are present. See our broader cortisol, stress and blood sugar guide for context.
