What is cortisol?
Cortisol is a steroid hormone produced by your adrenal glands, two small glands that sit on top of your kidneys. It plays a central role in your body's stress response, blood sugar regulation, blood pressure, immune function, inflammation and sleep-wake cycles. Cortisol release is controlled by a feedback loop between the hypothalamus, pituitary gland and adrenal glands, known as the HPA axis.
Cortisol follows a strong daily rhythm, peaking in the early morning to help you wake and gradually falling throughout the day to support sleep. Testing usually measures cortisol in blood, saliva or urine, with results reported in nmol/L in Australia, and the time of collection matters significantly. You can read more in our complete guide to the cortisol blood test in Australia.
Why does cortisol matter for long-term health and wellbeing?
Cortisol is essential for daily functioning, but consistently high or dysregulated levels are linked to a wide range of health issues. Chronically elevated cortisol has been associated with insulin resistance, weight gain around the middle, high blood pressure, cardiovascular risk, poor sleep, mood changes, weakened immunity, reduced bone density and cognitive changes. Persistently low cortisol, on the other hand, can leave you feeling exhausted, dizzy, weak and unable to cope with normal stress.
Cortisol is also closely tied to blood sugar and metabolic health, since it prompts the liver to release glucose and can contribute to insulin resistance over time. Understanding how your cortisol rhythm behaves gives useful insight into how well you are recovering from stress, sleeping and managing energy. You can read more on this in our article on how stress affects blood sugar levels, and cortisol is one of the hormone markers Vively considers as part of its baseline health testing.
What is an ideal cortisol level?
In Australia, reference ranges vary between labs and depend heavily on when the sample is taken. A morning (8 am) serum cortisol is typically 140 to 700 nmol/L, an afternoon (4 pm) sample generally 85 to 460 nmol/L, and a late-night level well below 50 nmol/L. Saliva testing measures the free, biologically active fraction and is often collected multiple times across a day to build a picture of the daily rhythm rather than a single point.
There is no single perfect number, and cortisol is unusual in that its pattern across the day is often more meaningful than any single reading. Interpretation depends on your age, sex, pregnancy status, medications (including corticosteroids and oral contraceptives), sleep, stress, illness, and other hormone markers. A trend over time and in the context of symptoms is often more informative than one isolated result.
What influences cortisol levels?
Stress is the most well-known driver, and both acute (short-term) and chronic (long-term) stress can raise cortisol. Sleep quality is another major influence, since disrupted or short sleep can flatten or reverse the normal daily rhythm, and shift work has a similar effect. Regular exercise usually supports a healthier cortisol rhythm, though very intense or excessive training without recovery can raise cortisol.
Diet also matters, particularly patterns high in refined carbohydrates, sugar and stimulants, which can amplify cortisol responses. Alcohol, caffeine, nicotine, blood sugar swings and skipping meals can all influence levels. Medications including corticosteroids, oral contraceptives (which raise total cortisol by increasing cortisol-binding globulin), hormone replacement therapy, opioids and some antidepressants can significantly affect results, as can pregnancy and menopause.
What are the symptoms of high cortisol?
Mild to moderate elevations often show up as ongoing fatigue that feels different from normal tiredness, difficulty falling or staying asleep, "wired but tired" feelings, sugar and salt cravings, and unwanted weight gain around the middle. Some people also notice mood changes, anxiety, irritability, brain fog, reduced tolerance to stress and low libido. Increased susceptibility to infections, high blood pressure, insulin resistance and elevated blood sugar can also appear.
More significant elevations (such as in Cushing's syndrome) may cause easy bruising, purple stretch marks on the abdomen, a rounded face, fat pads at the back of the neck, thinning skin, muscle weakness, weak bones and, in women, unwanted hair growth or menstrual changes. These are red flags that need urgent medical review. Because symptoms overlap with many other conditions, testing and context matter far more than symptom checklists.
What causes high cortisol?
The most common driver of elevated cortisol is chronic psychological, emotional or physical stress, often combined with poor sleep, over-training, blood sugar swings or high stimulant use. Depression, chronic pain, obesity, obstructive sleep apnoea and eating disorders can also raise cortisol levels. Medications, particularly corticosteroids taken by mouth, inhaled at high doses, injected or applied topically over large areas, are another common cause and can produce identical effects to naturally high cortisol.
Cushing's syndrome, though relatively rare, is a medical condition where the body produces or is exposed to too much cortisol. Causes include a pituitary tumour that overproduces ACTH (Cushing's disease), an adrenal tumour, ectopic ACTH-producing tumours or prolonged corticosteroid use. Any significantly high cortisol result or clinical suspicion of Cushing's syndrome requires specialist assessment.
What are the symptoms of low cortisol?
Low cortisol can cause persistent fatigue that does not improve with rest, muscle weakness, weight loss, poor appetite, nausea, low blood pressure, dizziness on standing, salt cravings, low blood sugar and reduced ability to cope with stress or illness. Mood changes such as low mood, apathy or irritability can also occur. In Addison's disease, additional signs may include darkening of the skin (particularly in creases, scars and gums), abdominal pain and, during severe stress or illness, an "adrenal crisis" which is a medical emergency.
Milder disruptions to the cortisol rhythm from chronic stress, poor sleep, over-training or shift work may not cause classic low cortisol symptoms, but can still leave people feeling exhausted, wired at night, unable to wake refreshed and struggling with recovery. These patterns often show up better on multi-point saliva testing than on a single morning blood test. Any suggestion of very low cortisol needs prompt medical review.
What causes low cortisol?
The most common causes of clinically low cortisol are primary adrenal insufficiency (Addison's disease, usually autoimmune), secondary adrenal insufficiency (where the pituitary is not producing enough ACTH) and abrupt withdrawal from long-term corticosteroid medication. Pituitary problems, previous head injury, radiation therapy, autoimmune conditions and rare genetic conditions can also cause low cortisol.
Less pronounced but functional disruptions to the cortisol rhythm can occur with chronic stress, burnout, poor sleep, over-training, shift work and significant illness. These are not the same as clinical adrenal insufficiency, but they can still affect wellbeing, energy and recovery. Any suspected adrenal insufficiency needs medical review promptly, as untreated low cortisol can become dangerous during illness or injury.
What does it mean if cortisol is outside the optimal range?
A high cortisol result may reflect ongoing stress, poor sleep, corticosteroid medication use, oral contraceptive use, pregnancy, obesity or, less commonly, an underlying medical condition such as Cushing's syndrome. It does not diagnose any single condition on its own, but persistent or significant elevations warrant further investigation. Timing of the test also matters, as morning results are naturally higher than afternoon or evening ones.
A low cortisol result may point to adrenal insufficiency, pituitary problems, recent corticosteroid use or acute illness. As with high cortisol, patterns matter more than isolated readings, and repeat testing is often needed. Both high and low results should be interpreted alongside symptoms, medications and related markers rather than in isolation.
Can cortisol be normal but something still be wrong?
Yes, cortisol has a strong daily rhythm, so a single morning reading may look normal even when the overall pattern is disrupted. Multi-point saliva testing can pick up flattened, delayed or reversed cortisol rhythms that a single blood test misses, particularly in people with chronic stress, burnout or shift work.
Medications and hormones can also affect results, particularly oral contraceptives and hormone replacement therapy, which raise cortisol-binding globulin and increase total serum cortisol without necessarily changing free cortisol. Biotin supplements, recent illness, timing of the sample and interpretation of the assay can also affect results. This is why cortisol is best interpreted alongside symptoms, sleep and other hormone markers rather than as a stand-alone number.
What other markers should be checked with cortisol?
ACTH is the most important companion marker when investigating cortisol abnormalities, as it helps distinguish between adrenal and pituitary causes. DHEA and DHEA-S, other adrenal hormones, add insight into overall adrenal function and are often used alongside cortisol to assess long-term stress patterns. Thyroid function (TSH, free T4, free T3) is another frequent companion, since the thyroid and adrenal systems often affect each other and share many overlapping symptoms.
Fasting glucose, HbA1c and fasting insulin help clarify metabolic effects of raised cortisol, as covered in our article on the connection between stress and blood sugar. Electrolytes (sodium, potassium), aldosterone and renin are relevant when adrenal insufficiency is suspected, and sex hormones (oestrogen, progesterone, testosterone, SHBG) provide broader hormonal context. Vitamin D, B12, iron studies and inflammation markers such as hs-CRP are also useful for fatigue investigations, and you can see the full set of markers Vively looks at through our tests page and shop tests page.
How can you improve cortisol to a healthier level?
Cortisol usually responds well to lifestyle change, particularly consistent sleep of 7 to 9 hours, regular daylight exposure in the morning, meals at regular times and gentle stress management practices such as breathwork, mindfulness or time outdoors. Regular movement supports a healthier cortisol rhythm, though very intense training without adequate recovery can worsen things, so balancing strength, cardio and rest matters. Reducing reliance on caffeine, alcohol and refined carbohydrates helps prevent unnecessary cortisol spikes.
Managing underlying stressors, whether work, relationships, chronic pain or unresolved health issues, is often the most important step, though not the easiest. Nutrient support (adequate protein, complex carbohydrates, magnesium, B vitamins and omega-3s) and treating any underlying conditions such as sleep apnoea, thyroid problems or depression can also help. Not every marker can or should be self-optimised, and Vively's how it works page explains how testing, monitoring and dietitian coaching combine to make sustainable change practical.
When does cortisol need medical review?
See your GP if your cortisol is significantly high or low, or if you have symptoms suggestive of Cushing's syndrome (such as easy bruising, purple stretch marks, rapid weight gain around the face and abdomen, muscle weakness and high blood pressure). Any symptoms suggestive of Addison's disease (such as persistent unexplained fatigue, weight loss, dizziness on standing, salt cravings, darkening of the skin or low blood pressure) also need prompt review, as untreated adrenal insufficiency can be dangerous.
Clinical review is important if you take corticosteroid medication long-term, are stopping or changing these medications, are pregnant, planning pregnancy, or have a history of pituitary or adrenal disease. Any suspected adrenal crisis (severe abdominal pain, vomiting, dehydration, confusion or fainting) is a medical emergency. Cortisol should never be self-diagnosed, as it is one piece of a bigger clinical picture your GP or endocrinologist can help you interpret.
How does Vively help you understand cortisol?
Vively looks at cortisol in the context of broader hormonal, metabolic and lifestyle health, alongside markers such as thyroid function, glucose, insulin, HbA1c, sex hormones, nutrient status and inflammation. Depending on the situation, this may include serum cortisol as part of the Vively Baseline Health Check or a more detailed multi-point saliva cortisol pattern to understand your daily rhythm and how stress is showing up in your body. Where relevant, your real-world glucose data from a continuous glucose monitor adds another layer of insight into how cortisol may be affecting your metabolism.
A registered nurse reviews your results with you one on one, and accredited practising dietitians support the changes that follow. Because your markers are retested over time, you can see how sleep, stress management, nutrition and lifestyle are actually shifting your cortisol pattern rather than guessing. Start at the Vively homepage or explore the full range of tests in the Vively shop.
References
- Royal College of Pathologists of Australasia. RCPA Manual: Cortisol. https://www.rcpa.edu.au/Manuals/RCPA-Manual/Pathology-Tests/C/Cortisol
- Healthdirect Australia. Cortisol blood test. https://www.healthdirect.gov.au/
- Better Health Channel, Victorian Department of Health. Adrenal glands. https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/adrenal-glands
- Royal Australian College of General Practitioners. Guidelines for preventive activities in general practice (Red Book). https://www.racgp.org.au/clinical-resources/clinical-guidelines/key-racgp-guidelines/view-all-racgp-guidelines/red-book
- Nieman LK, Biller BM, Findling JW, et al. The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism. 2008;93(5):1526 to 1540.
- Bornstein SR, Allolio B, Arlt W, et al. Diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism. 2016;101(2):364 to 389.
- McEwen BS. Physiology and neurobiology of stress and adaptation: central role of the brain. Physiological Reviews. 2007;87(3):873 to 904.
- Australian Prescriber. Adrenal insufficiency: identification and management. https://www.nps.org.au/australian-prescriber
- Chan S, Debono M. Replication of cortisol circadian rhythm: new advances in hydrocortisone replacement therapy. Therapeutic Advances in Endocrinology and Metabolism. 2010;1(3):129 to 138.
- National Institutes of Health, MedlinePlus. Cortisol test. https://medlineplus.gov/lab-tests/cortisol-test/
- Cleveland Clinic. Cortisol. https://my.clevelandclinic.org/health/articles/22187-cortisol
- Mayo Clinic. Cortisol test. https://www.mayoclinic.org/
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