The stress response evolved for short-term survival. Cortisol mobilises energy, sharpens focus, suppresses inflammation temporarily, and prepares the body for physical action. In the ancestral environment, stressors were acute and time-limited. In the contemporary environment, for many adults in their forties and fifties, stress is chronic, low-grade, and unresolved. The cortisol system was not designed for this, and prolonged activation of it has predictable downstream consequences for virtually every other hormonal system in the body.
The Cascade of Hormonal Suppression
Chronically elevated cortisol suppresses the hypothalamic-pituitary-gonadal axis, reducing testosterone production in both men and women. It inhibits thyroid hormone conversion from T4 to T3. It promotes insulin resistance and raises fasting blood glucose. It suppresses growth hormone release during sleep. It disrupts the circadian rhythm of other hormones including melatonin and DHEA. This is not a list of separate problems. It is a description of a single system being driven out of balance by one chronically elevated signal.
The Measurement Problem
A single morning cortisol blood test captures cortisol at one point in its daily cycle and misses the full picture. The most clinically useful assessment is a four-point salivary cortisol test measuring levels at waking, mid-morning, afternoon, and late evening. This maps the diurnal rhythm and reveals whether the pattern is flat, inverted, or dysregulated in ways that a morning blood test alone cannot show. Many people with significant HPA axis dysregulation have a morning cortisol within the normal range.
Sources
- Sapolsky, R.M. (2004). Why Zebras Don't Get Ulcers. Henry Holt and Company.
- McEwen, B.S. (1998). Stress, adaptation, and disease: allostasis and allostatic load. Annals of the New York Academy of Sciences, 840, 33-44.
- Chrousos, G.P., & Gold, P.W. (1992). The concepts of stress and stress system disorders. JAMA, 267(9), 1244-1252.