Cortisol is the body’s primary stress hormone, produced by the adrenal glands in response to signals from the hypothalamic-pituitary-adrenal (HPA) axis. Often called the “stress hormone,” cortisol plays essential roles in metabolism, immune function, and the body’s response to threat. However, chronic elevation is strongly associated with accelerated aging and disease.
Physiological Functions
Acute Cortisol Release (Adaptive):
- Mobilizes glucose from liver glycogen stores
- Increases alertness and cognitive focus
- Suppresses non-essential functions (digestion, reproduction, immune response)
- Facilitates the fight-or-flight response
- Promotes survival during acute stress
Normal Diurnal Rhythm: Cortisol follows a predictable daily pattern essential for health:
- Peak: 30-45 minutes after waking (cortisol awakening response)
- Gradual decline: Throughout the day
- Nadir: Around midnight during sleep
This rhythm is entrained by the circadian clock and morning light exposure. Disrupted cortisol rhythm is associated with metabolic dysfunction, depression, and increased mortality.
Cortisol and Aging
Chronic Cortisol Elevation (Maladaptive):
When stress is persistent and unresolved, cortisol remains elevated, producing pathological effects:
- Hippocampal atrophy: The hippocampus, critical for memory and emotional regulation, is rich in glucocorticoid receptors and vulnerable to cortisol-induced damage (McEwen, 2008)
- Muscle catabolism: Cortisol promotes protein breakdown, contributing to sarcopenia
- Visceral fat accumulation: Elevated cortisol drives fat deposition in the abdominal region
- Insulin resistance: Cortisol antagonizes insulin action, promoting hyperglycemia
- Immune suppression: Chronic elevation impairs immune surveillance and wound healing
- Telomere shortening: Stress-induced cortisol elevation accelerates cellular aging (Epel et al., 2004)
- Inflammation: Paradoxically, chronic cortisol exposure can promote inflammatory gene expression
Measurement
Salivary Cortisol:
- Non-invasive home testing
- Best assessed at multiple time points (morning, evening, awakening response)
- Useful for assessing rhythm and chronic stress
Blood Cortisol:
- Single morning measurement common
- Normal range: 6-23 mcg/dL (morning)
- Less useful than diurnal pattern assessment
Hair Cortisol:
- Reflects average cortisol over 1-3 months
- Useful for chronic stress assessment
- Growing research application
Optimization
Healthy cortisol regulation involves:
- Morning light exposure: Strengthens cortisol awakening response and diurnal rhythm
- Consistent sleep schedule: Supports normal cortisol rhythm
- Stress management: Breathwork, meditation, and social connection reduce chronic cortisol
- Exercise: Acute elevation is normal; regular training improves stress resilience
- Avoiding evening stimulation: Bright lights and stress late in the day disrupt rhythm
Connected Concepts
- Stress and Mindset: Comprehensive protocols for cortisol regulation
- Sleep: Bidirectionally linked with cortisol rhythm
- Circadian Rhythm: Master regulator of cortisol timing
- Glucose: Cortisol directly influences blood sugar
- Inflammation: Complex relationship with cortisol signaling
Key Research
- McEwen (2008): Central effects of stress hormones in health and disease
- Epel et al. (2004): Accelerated telomere shortening in response to chronic stress
- Sapolsky (2004): Comprehensive review of glucocorticoid effects on the brain
Last updated: 2026-01-01