Cortisol — Ray Peat & Georgi Dinkov Summary

Overview

Cortisol is the body's emergency backup hormone. It keeps you alive when normal healthy metabolism has failed. Its job is to break down your own tissues (thymus, muscle, skin, bone, eventually liver and intestine) and convert that protein into sugar so the brain and red blood cells can keep functioning. This makes it indispensable in a true crisis but ruinous as a chronic state. Sustained elevation produces most of the typical signs of aging. The way out of chronic cortisol is to consume adequate sugar, maximise thyroid function, and restore the protective steroids: pregnenolone, progesterone, DHEA, and testosterone. These things allow you to tolerate stress without resorting to this destructive backup mode.

Key Points

Cortisol is an emergency hormone, not a maintenance hormone. It exists for situations where normal healthy metabolism cannot keep up. Sugar, thyroid hormone, vitamin A, and the protective steroids (pregnenolone, progesterone, DHEA, testosterone) are what should be running daily physiology.
Cortisol maintains blood sugar by cannibalising body tissues. When glycogen runs out, adrenaline first tries to release the last reserves; if that fails, cortisol takes over and starts breaking down protein into glucose. The thymus and other immune tissues go first, then skeletal muscles, then skin, and finally liver and intestine. Under intense stress the thymus can be dissolved in roughly three hours.
Sugar lowers cortisol; fasting and low-carb diets raise it. Many so-called type 2 diabetics actually have high cortisol driving the high blood sugar, and giving them sugar paradoxically lowers both. Monkeys deprived of fruit develop very high cortisol. Fasting, ketogenic diets, and protein-only meals reliably push cortisol up because the body must break down its own tissues to produce glucose. People who fast for a week or two typically lose more muscle than fat.
Chronic cortisol weakens blood vessels, skin, and bone. Within two or three hours of a big dose, the thymus, skin, and muscles begin shrinking. Long-term elevation produces petechial hemorrhages, easy bruising (commonly on the thighs and upper arms in women), thin skin, weak capillaries, and osteoporosis. Continued for years it leads to strokes and the typical aging conditions. Cortisol-driven fat redistribution lays down fat in the trunk, neck, and face, the opposite pattern from estrogen-driven hip and thigh fat.
Cortisol causes weight gain, especially visceral fat around the midsection. Elevated cortisol lowers basal metabolic rate, blocks the insulin receptor, increases the activity of fatty acid synthase, and signals the body to hoard incoming calories as fat. Mid-section fat is the classic symptom of high cortisol. Human trials with cortisol blockers and 11-beta-HSD1 inhibitors have produced sustained fat loss without any change in calories, exercise, or macronutrients, which establishes weight gain as an endocrine problem rather than a calorie problem.
The cortisol-to-DHEA ratio is the single best predictor of all-cause mortality and morbidity. Multiple studies have shown that whether measured in blood, hair, or nails, this ratio outperforms other biomarkers for predicting future disease across categories: cancer, cardiovascular disease, depression and diabetes. The ratio should be below 0.3 in optimal health, and crossing 0.5 already predicts diagnosable pathology. After major surgery, a ratio above 30 within 48 hours is essentially fatal. Cortisol-to-testosterone is a male-specific version where above 20 reliably predicts obesity and above 30 predicts diabetes.
Cortisol forms positive feedback loops with serotonin and estrogen, creating the stress cascade. Cortisol activates aromatase (which produces estrogen) and tryptophan hydroxylase (which produces serotonin). Both estrogen and serotonin then go back and activate 11-beta-HSD1 to synthesize more cortisol. This means once chronic stress is established, the cycle feeds itself and will not stop without intervention. Estrogen alone can fully trigger cortisol synthesis at the adrenal level without the brain even perceiving stress.
Cortisol is suppressed by the protective steroids: progesterone, pregnenolone, DHEA, testosterone. Someone saturated with these can take a cortisol pill or prednisone with very little harm. Hans Selye's adrenal-removed rats died from minor stress, but the same animals given daily progesterone lived out a full healthy lifespan. A massive 10 gram pregnenolone dose normalised high cortisol in stressed rats without raising the cortisol of unstressed animals, showing that supplementation upstream stabilises the system rather than driving it.
Estrogen and serotonin are major activators of cortisol production. Estrogen acts directly on the adrenal cortex to drive cortisol output, and it activates the enzyme tryptophan hydroxylase that produces serotonin. Serotonin in turn powerfully stimulates corticotropin-release hormone (CRH) in the hypothalamus and acts directly on the pituitary. Estrogen-induced asthma worsens at night because all the stress hormones rise during darkness.
Aspirin, emodin, and the neurosteroids inhibit cortisol synthesis at the tissue level. Salicylic acid, the metabolite of aspirin, is an inhibitor of 11-beta-HSD1, the enzyme that synthesises cortisol. A single tablet produces a several-hour window of reduced cortisol production. Emodin, the active compound in cascara sagrada, is the most potent natural inhibitor of 11-beta-HSD1 known, active at nanomolar concentrations, and it also activates 11-beta-HSD2 which deactivates cortisol. Progesterone does the same dual action and additionally blocks the cortisol receptor directly.
No organ except the heart is fully protected from cortisol. The gastrointestinal tract, muscles and brain have the highest expression of the glucocorticoid receptor. Cortisol shreds brain tissue and causes measurable atrophy on MRI, particularly in the prefrontal cortex, which is why people with chronic depression have smaller brain volume. The heart is relatively protected because in males it contains very high testosterone and in females very high progesterone, both glucocorticoid antagonists. When even the heart starts atrophying in extreme illness, doctors know the end is near.
Cortisol peaks at dawn because glycogen runs out overnight. When the lights go out, adrenaline begins rising within about 15 minutes. By morning, cortisol is at its daytime peak. The blood is thicker in the morning and there is a corresponding peak in deaths from strokes and heart attacks. In one study, morning jogs on an empty stomach broke the chromosomes of white blood cells. Eating before the run stopped this reaction. Hot showers and intense exercise before breakfast are similarly stressful.
"Adrenal fatigue" is a misreading of Selye. Selye described three phases of stress: shock, adaptation, and exhaustion. He did not describe fatigue. In the exhaustion phase the animal died. Out of thousands of blood tests reviewed, only one or two showed actual cortisol deficiency. What people call adrenal fatigue is almost always low pregnenolone, progesterone, and DHEA combined with high cortisol.

Notable Quotes

"Cortisol is the stress hormone that keeps you alive but under an unhealthy metabolism."

[Sarah Murray — Hot Flashes, Night Sweats, Stress, Aging, PMS, and Sugar Metabolism]

"Having some of these people test their cortisol, we saw that very many of these so-called diabetics had very high cortisol, and sugar happens to be the best thing for lowering cortisol to normal."

[Ray Peat — Glycemia, Starch and Sugar in Context]

"I think there's hardly a chronic condition where you cannot look at the condition and don't see cortisol implicated."

[Georgi Dinkov — Crucial Facts About Your Metabolism, Interview With Georgi Dinkov]

"Within the first two or three hours of a big dose of cortisol or the synthetic glucocorticoids, the thymus gland starts shrinking. The skin and muscles begin shrinking as the cortisol shifts the metabolism in the opposite direction of testosterone."

[Ray Peat — Endocrinology Part 3]

"Cortisol will make you fat while simultaneously destroying your lean tissue."

[Georgi Dinkov — How to Naturally Lower Cortisol & Optimize Your Health with Georgi Dinkov]

"Out of thousands of blood tests, I've only seen one or two that were deficient in cortisol."

[Ray Peat — Insulin Resistance, Vegans, Low Cortisol]

"If you don't have enough pregnenolone, DHEA, and progesterone, you need cortisol to handle stress. But the way it handles stress is to depress inflammation, but it does it at the expense of tissues such as your thymus gland, muscle, skin, and liver."

[Ray Peat — Thyroid and Regeneration]

Important Things To Consider

Topical and inhaled corticosteroids cause the same systemic damage as oral cortisol. Aerosolised inhalants for asthma and topical creams for eczema and psoriasis produce the same shrinkage of thymus, skin, and muscle and the same blood vessel weakening. Years of this kind of treatment cause real harm even though the doses sound small.

Even "physiological" cortisol supplementation causes Cushing's signs. Patients given a 20 mg per day divided dose of natural hydrocortisone, supposedly matching what the body normally makes, all started developing puffy faces typical of Cushing's disease within two or three months. Tiny doses (5 to 10 micrograms) for a specific issue like menstrual disturbance can be useful, but supplementing at endogenous physiological amounts is risky.

Lowering cholesterol with statins forces increased reliance on cortisol. Cholesterol is the raw material for the protective steroids. If you cut it pharmacologically, the body cannot make adequate progesterone, pregnenolone, and DHEA, and falls back on cortisol to handle stress. This is part of why statin users develop muscle breakdown, hair loss, and the broader degenerative profile.

Cortisol blocks the conversion of T4 to T3, deepening hypothyroidism. In vitro work shows cortisol inhibits the deiodinase enzymes that activate thyroid hormone. So once you slip into the high-cortisol, low-thyroid state, the cortisol itself perpetuates the thyroid problem. It is a self-reinforcing trap that takes deliberate work (good food, sugar, thyroid support and rest) to escape.

Synthetic glucocorticoids cause inflammation rebound when stopped. Prednisone, dexamethasone, and similar drugs suppress visible inflammation while upregulating COX, LOX, NF-kB, and TNF-alpha behind the scenes. When the drug stops, inflammation returns at two to three times baseline, which is why people end up unable to wean off. Endogenous cortisol does the same thing in the long run, increasing the very inflammatory pathways it acutely suppresses.

Cortisol resistance develops with chronic exposure and requires receptor antagonism to reset. When cortisol stays elevated for too long, the cortisol receptors downregulate. The body's response is to produce even more cortisol to overcome the resistance. Most people over 30 have some degree of mild to moderate cortisol resistance. Things that block the cortisol receptor (pregnenolone, progesterone, DHEA) actually re-sensitise the receptors and let baseline production drop.

Aging tilts steroid production toward cortisol at the expense of DHEA and pregnenolone. With age the adrenal layer that produces DHEA and pregnenolone tends to atrophy while the cortisol-producing layer remains. This means a "moderate" cortisol level in an older person, in the context of low protective steroids, can still be eating the muscles and skin and eventually deteriorating the heart, lungs, and brain.

Cortisol is not produced only by the adrenals. The skin can make cortisol when stressed, and other peripheral tissues are potential cortisol producers. CRH itself is produced not just in the brain but in peripheral tissues. So even people without adrenal glands experience some local cortisol activity and removing the adrenals does not eliminate stress-driven tissue breakdown.

Anorexia and chronic restrictive dieting visibly shrink the brain. MRI scans of anorexic patients show frontal lobe shrinkage during starvation that rebuilds on refeeding. Around three years of psychological depression, which raises cortisol, also produces measurable brain volume reduction. The damage is repairable but only after the stress is stopped.

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