Salivary Cortisol and Diurnal Curve
The biomarker of chronic stress — its PATTERN matters more than the spot value
Definition
Cortisol is the main hormone of the hypothalamic-pituitary-adrenal (HPA) axis, released in circadian pulses: peak upon awakening (CAR, Cortisol Awakening Response), progressive decline throughout the day, and overnight minimum. Saliva measurement (4-5 samples throughout the day) reflects biologically active free cortisol, unlike plasma cortisol which measures the protein-bound fraction. The shape of the curve — not just the absolute value — is what predicts health, longevity, and disease risk.
Detailed explanation
Dysregulated patterns identifiable on a diurnal curve:
Flat curve: low morning cortisol and high night-time cortisol — classic indicator of advanced chronic stress, burnout, functional adrenal fatigue. Hyper-responder: exaggerated CAR >180% of baseline — suggests anxiety, hypervigilance. Hypo-responder: CAR <50% of expected rise — associated with depression, PTSD, fibromyalgia. Elevated night-time cortisol: predicts maintained insomnia, nocturnal insulin resistance, and sarcopenia.
Mechanisms of chronically elevated cortisol: collagen and extracellular matrix degradation (accelerated skin ageing), bone mass loss, hippocampal atrophy (neurotoxic effect documented by Sapolsky), immune suppression (especially NK cells), abdominal lipogenesis, and insulin resistance.
Interventions that normalise the curve: 8-week mindfulness meditation (MBSR — documented 25% CAR reduction), Ashwagandha KSM-66 adaptogens, >7.5 h night sleep, early morning sunlight exposure (circadian rhythm reset), cognitive-behavioural therapy, and reduction of morning caffeine in hypersensitive people.
Scientific sources
Related terms
Interested in related treatments?
Generate My Protocol