Sleep, stress and recovery

Cortisol

Also called: stress hormone

Cortisol is the body's main stress hormone, made by the adrenal glands. It rises in the morning to wake you up, falls through the day, and surges briefly during stress. The 'high cortisol = belly fat = inflammation' framing on social media oversimplifies. Most healthy people have normal cortisol. Real cortisol problems are uncommon and need a doctor; what most people experience is normal variation amplified by sleep loss, stress, alcohol, and chronically high caffeine.

What cortisol does

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 spike 30-50 percent in the first 30 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.

What 'high cortisol' actually means

  • 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.

What actually lowers cortisol

  1. Sleep 7-9 hours regularly. The strongest cortisol-modulating intervention by far. One night of 4 hours raises next-day cortisol by 30 percent.
  2. Reduce alcohol. Even moderate drinking elevates next-morning cortisol.
  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. Moderate exercise lowers baseline cortisol; chronic high-intensity training without recovery raises it.
  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.

What doesn't work (despite the marketing)

  • '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.

Cortisol and the gut

High morning cortisol after a bad night of sleep slows gut motility for the day, increases water retention, and can cause more bloating that morning. 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.

Common questions

Should I get my cortisol tested?
Only if you have symptoms suggesting Cushing's (round face, central weight gain with thin limbs, purple stretch marks, easy bruising) or Addison's (chronic fatigue, hyperpigmentation, salt cravings, low blood pressure). Otherwise testing has poor specificity for everyday stress.
Does ashwagandha lower cortisol?
Some evidence for small reductions in chronically stressed adults at 300-600 mg of standardised extract daily. Effect size is modest. Not for everyone, can interact with thyroid medication and is not safe in pregnancy.
Why do I wake up at 3am every night?
Could be cortisol-related, but more often it's blood sugar dipping, alcohol metabolism (the 4-hour rebound after evening drinks), perimenopause (in women 40+), or untreated sleep apnoea. Cortisol is one cause among several. A sleep journal often clarifies the pattern.
Does intermittent fasting raise cortisol?
Brief, transient rises are normal during fasting periods. Chronic problems with fasting and cortisol are mostly seen in already-stressed people, especially women with disordered eating histories. For most healthy adults a 14-16 hour fast is fine. Watch for fatigue, sleep disruption or mood changes; back off if they appear.

Sources