Cortisol is a steroid hormone produced by the adrenal glands in response to stress and low blood sugar. It follows a daily (circadian) rhythm: highest within 30–45 minutes of waking (the 'cortisol awakening response'), declining through the day, and lowest around midnight. Chronic elevation disrupts this rhythm and drives a cascade of metabolic, immune and psychological effects.
What cortisol does
Cortisol is essential for survival. In acute stress, it mobilises glucose, suppresses inflammation, sharpens alertness and primes the cardiovascular system for action. Without it, the body cannot mount a stress response — a rare and life-threatening condition called Addison's disease.
The problem is not cortisol itself but its chronic dysregulation. When the stress response is activated repeatedly without adequate recovery, cortisol remains elevated and its beneficial short-term effects become harmful long-term ones.
Effects of chronically elevated cortisol
- Central weight gain — cortisol promotes fat storage around the abdomen
- Raised blood pressure — cortisol sensitises blood vessels to adrenaline
- Impaired glucose regulation — elevated cortisol raises blood sugar, worsening insulin resistance
- Immune suppression — reducing the body's ability to fight infection
- Sleep disruption — cortisol should be low at night; elevated levels delay sleep onset and reduce deep sleep
- Bone loss — long-term high cortisol reduces bone mineral density
- Memory and mood — excess glucocorticoids damage the hippocampus and are associated with depression and anxiety
How cortisol is tested
A morning serum cortisol — taken between 8–9 am when levels are naturally highest — is the most common test. A level below 100–140 nmol/L raises concern for adrenal insufficiency; above 500 nmol/L is unlikely to reflect deficiency. Ambiguous morning results are followed by a short Synacthen stimulation test.
For suspected Cushing's syndrome (pathologically elevated cortisol from a tumour), testing includes a 24-hour urinary free cortisol, late-night salivary cortisol (which should be very low), or an overnight low-dose dexamethasone suppression test.
Lifestyle-based cortisol management
Chronic stress is not a lab abnormality — it is a physiological state. The most effective evidence-based approaches to managing cortisol in the context of chronic stress are: consistent sleep (7–9 hours, consistent timing), regular moderate-intensity exercise (which acutely raises cortisol but lowers the baseline over time), mindfulness and breath-based interventions (which activate the parasympathetic nervous system), and reducing caffeine after midday (which extends cortisol's half-life).
"High cortisol is often not a pathological finding — it is a signal that the body's stress system has been running too hard for too long. The first question is always: what is sustaining it?"
Dr. Lina Haddad, CMO, Looms
When to investigate clinically
See your doctor if you have unexplained central weight gain, easy bruising, purple stretch marks on the abdomen, muscle weakness, or high blood pressure that is resistant to treatment. These are signs of Cushing's syndrome — a rare but serious condition of cortisol excess — rather than lifestyle-related cortisol elevation.