What Is Cortisol?
Cortisol is a steroid hormone produced by the adrenal cortex. It is the body's primary stress hormone — central to the regulation of metabolism, immune function, sleep, blood pressure, and inflammation.
Cortisol follows a distinct daily pattern: highest in the early morning (within 30–45 minutes of waking), declining through the day, and lowest in the evening.
What Cortisol Regulates
- Blood glucose — raises blood sugar via gluconeogenesis; chronically elevated cortisol drives insulin resistance
- Immune function — acutely anti-inflammatory; chronically suppresses immune function
- Metabolism — promotes fat storage, particularly visceral and abdominal fat
- Sleep — elevated evening cortisol directly disrupts sleep onset and quality
- Muscle and bone — chronically elevated cortisol is catabolic
- Mood and cognition — chronic elevation associated with anxiety, depression, and cognitive impairment
Acute vs. Chronic Cortisol Elevation
Acute elevation is normal and adaptive. Chronic elevation from unresolved stress, poor sleep, or overtraining causes insulin resistance, visceral fat accumulation, immune suppression, sleep disruption, muscle loss, and HPA axis dysregulation.
Cortisol Reference Ranges (Morning, Fasting)
Below 100 nmol/L: Low. 100–200: Low-normal. 200–550: Normal morning range. Above 700: Elevated.
How to Bring Cortisol Into Balance
- Sleep — the most powerful single lever
- Exercise type and timing — moderate-intensity reduces cortisol over time
- Stress reduction practices — mindfulness, breath work, nature exposure
- Caffeine timing — wait 90 minutes after waking
- Social connection — genuinely protective
- Adaptogenic herbs — ashwagandha, rhodiola have evidence for modest cortisol reduction
Is Cortisol Tested in a Standard Physical?
Rarely. Stem Health includes morning cortisol and DHEA-S in the adrenal panel of the Core and Horizon Assessments.
