Cortisol
The primary stress hormone — regulates metabolism, immune function, and the body's fight-or-flight response.
Optimal Range
6-18 μg/dL (morning, optimal) · Context-dependent
Risk-Stratified Targets
| Population / Context | Target |
|---|---|
| Morning serum — optimal | 8–15 μg/dL |
| Morning serum — normal range | 6–18 μg/dL |
| Morning serum — elevatedInvestigate if persistent; consider Cushing's workup | > 20 μg/dL |
| Morning serum — lowConsider adrenal insufficiency | < 5 μg/dL |
Why It Matters
Chronically elevated cortisol accelerates aging through muscle wasting, bone loss, immune suppression, and visceral fat accumulation. Dysregulated cortisol is a hallmark of chronic stress and HPA axis dysfunction.
Understanding Cortisol
Cortisol is the body's primary glucocorticoid hormone, produced by the adrenal glands under the control of the hypothalamic-pituitary-adrenal (HPA) axis. In acute stress, cortisol mobilizes glucose, suppresses inflammation, and sharpens alertness — a life-saving response. The problem arises when this system is chronically activated, as occurs with persistent psychological stress, sleep deprivation, overtraining, or chronic illness.
Chronic cortisol elevation drives a recognizable pattern of accelerated aging: visceral fat accumulation (particularly abdominal), muscle wasting (catabolic effect on protein), bone loss (cortisol directly inhibits osteoblasts), immune suppression, impaired wound healing, elevated blood sugar, hypertension, and cognitive impairment (hippocampal damage). This cluster of effects resembles premature aging — and indeed, Cushing's syndrome (pathological cortisol excess) produces dramatic premature aging.
Interpreting cortisol requires attention to timing and methodology. Serum cortisol follows a strong circadian rhythm — highest in the early morning (6–8 AM) and lowest around midnight. A single morning blood draw only captures one point in this curve. Four-point salivary cortisol testing (morning, noon, evening, bedtime) provides a much more complete picture of HPA axis function and is increasingly used in functional and longevity medicine to detect both cortisol excess and the 'flat' cortisol curve seen in chronic stress and burnout.