Cortisol

Cortisol is essential for life. It mobilises glucose, suppresses inflammation, supports blood pressure, sharpens attention during stress, and maintains the daily wake-sleep rhythm. Mornings have a 'cortisol awakening response' where levels rise sharply, by roughly 50 percent on average, in the first 30 to 45 minutes after waking. Levels then decline through the day, reaching their lowest around midnight. Stress, illness, infection, low blood sugar and exercise all push it temporarily higher.

• True medical hypercortisolism is rare (Cushing's syndrome, UK incidence around 0.7-2.4 cases per million per year, with point prevalence higher around 40-70 per million because cases accumulate). It causes a specific cluster: round face, central weight gain, purple stretch marks, easy bruising, muscle weakness, high blood sugar, high blood pressure. This needs a doctor.
• What most people call 'high cortisol' is normal cortisol pushed around by lifestyle: chronic short sleep, ongoing stress, high alcohol, high caffeine.
• Saliva cortisol curves can show flattened (less morning rise, less evening fall) which is associated with chronic stress but not a disease itself.
• Cortisol blood tests done randomly are nearly useless because of the daily rhythm. A 24-hour urine cortisol or a midnight saliva test is needed for proper assessment.

1. Sleep 7-9 hours regularly. The strongest cortisol-modulating intervention by far. One night of 4 hours' sleep raises cortisol the following evening by about 37 percent.
2. Reduce alcohol. Regular and heavy drinking activates the HPA axis and raises cortisol; effects of moderate drinking are smaller and less consistent.
3. Cap caffeine at 200 mg before noon. Late afternoon caffeine raises cortisol AND fragments sleep AND raises next-morning cortisol.
4. Move daily, but don't overtrain. Regular moderate exercise generally keeps the cortisol response in check; chronic high-intensity training without recovery (overtraining) can raise cortisol.
5. Time outdoors in morning daylight. Helps the cortisol awakening response and the evening drop.
6. Slow breathing, meditation, yoga, or simply long walks. All show modest cortisol-lowering effects in trials.
7. Eat regularly. Skipping meals or extreme fasting can raise cortisol in stressed people.

• 'Cortisol-lowering' supplements (ashwagandha, phosphatidylserine, rhodiola). Some have small effects in stressed populations. Most are oversold.
• Adrenal cocktails (orange juice, salt, cream of tartar) trending on TikTok. No evidence. The premise is biologically incoherent.
• Cleanses, detoxes, parasite cleanses. None of these are connected to cortisol regulation.
• Hair cortisol tests sold direct-to-consumer. Useful in research, not clinically actionable for individuals.
• 'Adrenal fatigue' as a diagnosis. Not recognised by endocrinology societies; the symptom cluster is real but the explanation isn't.

Acute stress, via cortisol and CRF signalling, can delay gastric emptying and accelerate colonic transit, which may worsen bloating after a bad night of sleep. Chronic stress also raises gut permeability and shifts the microbiome composition. Most gut issues that 'come and go with stress' are mediated through cortisol and the autonomic nervous system, not because of one specific food.