The HPA Axis and Cortisol Regulation

The hypothalamic-pituitary-adrenal (HPA) axis controls cortisol production. Stress triggers the hypothalamus to release CRH, stimulating the pituitary to release ACTH, which signals the adrenal cortex to produce cortisol. Cortisol then feeds back to suppress CRH and ACTH. Under chronic stress, this system can become dysregulated. Initially, cortisol output is chronically elevated (driving insulin resistance, muscle wasting, immune suppression, and sleep disruption). Eventually, the HPA axis may downregulate, leading to low cortisol output (causing fatigue, hypotension, and poor stress tolerance).

1

Diurnal Rhythm Matters

Cortisol should be highest in the morning (waking you up) and lowest at night (allowing sleep). A flattened or inverted rhythm indicates HPA axis dysfunction.

2

Drives Reverse T3

Chronic cortisol elevation shifts thyroid hormone conversion from active T3 to inactive Reverse T3, causing hypothyroid symptoms despite normal TSH.

Optimal Cortisol Benchmarks

Functional Range (Hormonal Focused) Morning optimal: 10-18 ug/dL; Evening: < 5 ug/dL
Standard Lab Range Standard morning: 6-23 ug/dL; Standard evening: 2-14 ug/dL

Common Questions

Can chronic stress really damage my health?

Yes. Chronically elevated cortisol promotes insulin resistance, visceral fat accumulation, bone loss, muscle wasting, immune suppression, sleep disruption, and cognitive decline. It is one of the most destructive hormonal imbalances.

What time should I test cortisol?

Morning cortisol (7-9 AM, fasting) is the standard test. For a complete picture, a 4-point salivary cortisol test throughout the day can assess your diurnal rhythm.