Biomarker Glossary

Cortisol

Cortisol is your main stress hormone, produced by the adrenal glands. It regulates blood sugar, blood pressure, inflammation and the sleep wake cycle. A cortisol blood test, ideally taken in the morning, is the standard UK screen for adrenal disorders and chronic stress.

Also known as: Stress Hormone, Hydrocortisone

Cortisol is most informative when read alongside related markers like TSH and Glucose. A single number rarely tells the whole story. If your reading sits outside the typical range, share the full report with your GP or healthcare professional before drawing conclusions.

What is Cortisol?

Cortisol is released in a daily rhythm, peaking around 30 to 60 minutes after waking and falling throughout the day to its lowest point around midnight. It rises in response to stress, low blood sugar, and physical demands.

Cortisol gives you energy, focus and alertness, mobilises glucose, suppresses inflammation, and helps regulate immune responses. Short term cortisol spikes are healthy. Chronically high cortisol drives weight gain, insulin resistance, anxiety, poor sleep and immune problems.

Persistently low cortisol can indicate adrenal insufficiency (Addison's disease) or pituitary problems. Persistently high cortisol can indicate Cushing's syndrome, chronic stress, or steroid medication exposure.

Why test Cortisol?

To investigate symptoms of chronic stress, fatigue, weight gain or sleep problems.
To screen for Cushing's syndrome (high cortisol) or Addison's disease (low cortisol).
If you have unexplained low blood pressure, dizziness on standing or salt cravings.
If you take long term steroid medication and want to monitor adrenal recovery.
As part of a stress, biohacking or burnout panel.

To investigate symptoms of chronic stress, fatigue, weight gain or sleep problems.

Cortisol normal range (UK)

Result	What it means
Morning (8 to 9am): 138 to 690 nmol/L	Normal
Below 138 nmol/L morning sample	Low. Possible adrenal insufficiency.
Above 700 nmol/L morning sample	High. May indicate Cushing's, severe stress or steroid use.
Evening (around 11pm): below 100 nmol/L	Expected low point

Cortisol must be interpreted with timing in mind. The same value at 8am and 8pm has very different meanings. UK labs typically use the 8am morning value as the diagnostic standard.

About these ranges. The ranges above are typical UK clinical lab ranges aligned to NHS and Royal College of Pathologists guidance. Your Chxhealth report will show the specific reference range used by our partner lab, Randox, for each marker. Lab ranges vary slightly between providers and assays. Always interpret your results in the context of the range printed on your own report.

What causes high Cortisol?

Acute or chronic psychological stress
Cushing's syndrome (pituitary, adrenal or ectopic tumour)
Steroid medication (prednisolone, dexamethasone)
Severe depression or anxiety
Heavy alcohol use
Pregnancy (normally raised)
Severe illness or infection

What causes low Cortisol?

Addison's disease (primary adrenal insufficiency)
Pituitary problems (secondary adrenal insufficiency)
Recent long term steroid use, then sudden withdrawal
Severe pituitary disease or surgery
HPA axis dysfunction from chronic stress (sometimes called adrenal fatigue, although this term is not formally recognised in mainstream UK medicine)

Symptoms of high Cortisol

Weight gain, particularly around the abdomen, face and back of the neck
High blood pressure
Insulin resistance, raised blood sugar
Easy bruising, thin skin, slow healing
Anxiety, irritability, low mood
Difficulty sleeping, particularly waking at 3 to 4am
Sugar and salt cravings
Muscle weakness
Stretch marks (purple or red)
Irregular periods in women, low libido in both sexes

Symptoms of low Cortisol

Severe fatigue, exhaustion
Dizziness on standing (postural hypotension)
Salt cravings
Loss of appetite, weight loss
Nausea or abdominal pain
Skin darkening (in Addison's)
Low blood sugar
In severe cases, adrenal crisis: collapse, vomiting, severe pain. This is a medical emergency.

How is Cortisol tested?

Cortisol is measured from a blood sample taken between 8am and 9am, when levels naturally peak.

Avoid stress, exercise and caffeine for at least 30 minutes before the test.

If you take hydrocortisone or other steroid medication, follow your doctor's instructions on whether to hold the dose.

For a fuller picture, salivary cortisol at multiple times of day can be tested separately to map the daily rhythm.

Chxhealth samples are analysed by Randox, a UK laboratory accredited by UKAS. Results return in 3 to 5 working days.

How to support healthy Cortisol levels

Prioritise consistent sleep (7 to 9 hours, regular bedtime). Sleep is the single biggest lever on cortisol.
Manage psychological stress: breathwork, meditation, time in nature, social connection all lower cortisol.
Limit caffeine, especially after midday.
Strength train rather than only doing prolonged endurance exercise, which can raise cortisol.
Eat regularly. Skipped meals raise cortisol in many people.
Avoid alcohol close to bedtime. It fragments sleep and raises overnight cortisol.

These are general lifestyle suggestions. Chxhealth is an information service. For personal medical advice, please speak to a healthcare professional.

Chxhealth panels that test Cortisol

10 Chxhealth biomarker panels include Cortisol. Each is analysed by Randox, a UK laboratory accredited by UKAS. Reports are delivered in 3 to 5 working days.

Cortisol FAQs

When is the best time to test cortisol?

Between 8am and 9am, when cortisol naturally peaks. A morning blood cortisol is the standard UK screening test. If a more detailed rhythm is needed, salivary cortisol at 4 points across the day is used.

Is "adrenal fatigue" real?

The term adrenal fatigue is not formally recognised in mainstream UK medicine. However, chronic stress can dysregulate the hypothalamic pituitary adrenal (HPA) axis, with very real symptoms. The right diagnostic terms are HPA axis dysfunction or, in more severe cases, adrenal insufficiency.

Can cortisol affect weight?

Yes. Chronically high cortisol drives central abdominal fat gain, insulin resistance and sugar cravings. It is one of the biggest hidden contributors to stubborn weight gain.

What is a synacthen test?

A diagnostic test for adrenal insufficiency. An injection of synthetic ACTH is given and cortisol is measured before and after to see if the adrenals respond. It is a hospital based test and not routinely available through Chxhealth.

Can I lower cortisol naturally?

Yes. Consistent sleep, stress reduction, regular meals, strength training (rather than chronic cardio), reduced caffeine and alcohol all lower cortisol. Effects can be seen within weeks.

Often tested with Cortisol

The biomarkers below are commonly investigated alongside Cortisol because they reveal connected aspects of the same physiological picture:

TSH: Stress and thyroid axes interact closely.
Glucose: Cortisol raises glucose. Pairing them shows the metabolic impact.
Testosterone: High cortisol can suppress testosterone.

Choose the right test for your goal

If you are reading about Cortisol because of a specific health goal, our buying guides walk you through which Chxhealth panels fit:

Sources and further reading

This page is informed by guidance from the NHS, NICE, Royal College of Pathologists and other UK authoritative bodies. For deeper detail or to verify the information, see:

About this page. Last reviewed: 13 May 2026. Next scheduled review: May 2027. This page has not yet been independently reviewed by a clinician. It is written from authoritative UK medical guidance (NHS, NICE, Royal College of Pathologists, peer-reviewed sources) but has not undergone formal clinical sign off.

Important. Chxhealth is a UK information service. We do not diagnose, treat or prescribe. The reference ranges and information on this page are general educational content and should not be used as a substitute for advice from a qualified healthcare professional. For any concerns about your health or results, please speak to your GP or another healthcare professional.