Cortisol has a bad reputation. On social media, it is blamed for a puffy face (“cortisol face”) or abdominal fat (“cortisol belly”), while drinks supposedly designed to lower it are sold. Yet this hormone helps us wake up in the morning, maintain blood glucose between meals and respond to danger. The problem is almost never having cortisol, but having it at the wrong time, for too long or, more rarely, in abnormal amounts because of a genuine disease.
The essentials
- Blood cortisol starts rising at around 3–4 am, peaks between 7 am and 9 am, then falls to very low levels around midnight.
- On waking, its secretion rises sharply for 30 to 45 minutes: this is normal.
- Endogenous Cushing’s syndrome affects 2 to 3 new people per million each year; prescribed corticosteroids remain the most common cause of excess.
- In a meta-analysis of 7 trials (488 participants), ashwagandha was associated with cortisol levels 1.16 µg/dL lower, with no significant effect on perceived stress.
What is cortisol and what does it do?
Cortisol is the body’s main glucocorticoid, produced by the cortex of the adrenal glands. Its secretion is controlled by the hypothalamic–pituitary–adrenal axis: the hypothalamus releases CRH, the pituitary responds with ACTH, which stimulates the adrenal glands. In turn, cortisol inhibits the hypothalamus and pituitary, preventing the system from going into overdrive.
It increases glucose availability by mobilising proteins and fats, modulates inflammation and immunity, and contributes to cardiovascular tone and the response to demands. This effect on glucose explains why a sustained excess can disrupt blood glucose regulation, as detailed in our article on insulin resistance, its mechanisms and tests.
Why is cortisol highest in the morning?
Because it follows a clock. In people with regular sleep schedules, it starts rising at 3–4 am, peaks between 7 am and 9 am, then declines to very low levels around midnight. The disappearance of this night-time trough is in fact one of the most typical abnormalities in Cushing’s syndrome.
There is also the cortisol awakening response: a marked rise during the 30 to 45 minutes after getting up, accompanying the transition to wakefulness. High cortisol at 8 am is therefore expected.
What interests researchers is the shape of the curve. A meta-analysis of 80 studies linked “flatter” slopes (little difference between morning and evening) to poorer health, with a modest association (r = 0.147), stronger for immune and inflammatory markers (r = 0.288). A flat curve may simply be a marker, rather than necessarily a cause.
Acute or chronic stress: what changes?
During a brief stressful event, cortisol rises and then falls: this is a useful, reversible response. Repeated demands without recovery can alter the daily rhythm.
This is where the “cortisol belly” myth comes from. Among 59 premenopausal women, those with predominantly abdominal fat secreted more cortisol in response to laboratory stressors, and the leanest of them did not get used to those stressors. This association does not prove that stress “creates” abdominal fat in everyone, or that a drink would melt it away.
Several situations also moderately raise cortisol without adrenal disease: pregnancy, depression, alcohol dependence, severe obesity, poorly controlled diabetes, pain or surgery, and intense, prolonged exercise. For other approaches related to stress, see our article on natural anti-stress ingredients studied in research.
“Cortisol face”, high cortisol: what does a genuine excess look like?
A genuine chronic excess is called Cushing’s syndrome. Over time, it combines predominantly central obesity, muscle wasting, hypertension and glucose intolerance. A rounded face does occur, but it reflects substantial, prolonged exposure, not a busy week.
- The most common cause is medication : prescribed corticosteroids. Guidelines therefore recommend reviewing treatments before any testing.
- The endogenous form is rare (2 to 3 cases per million each year): excess ACTH from a pituitary or ectopic source, or autonomous overproduction by an adrenal gland.
If several signs accumulate and worsen, it is for a doctor to decide whether to investigate, not a test bought online.
What does low cortisol mean?
A genuine deficiency is called adrenal insufficiency. Its primary form (Addison’s disease) affects around 100 to 140 people per million, with 4 new cases per million each year in Western countries, and is autoimmune in up to 90% of cases. Its symptoms (fatigue, weakness, weight loss, abdominal pain) are non-specific, apart from salt craving, which often delays diagnosis. Persistent fatigue therefore deserves medical advice rather than an “adrenal fatigue” label.
How is cortisol measured, and why is one test not enough?
Cortisol varies from hour to hour: a randomly taken measurement tells us very little, and guidelines advise against using it to investigate Cushing’s syndrome. Each test answers a specific question.
| Test | Procedure | What it looks for | Guideline reference point |
|---|---|---|---|
| Morning blood cortisol | Blood sample at around 8 am | A deficiency | Below 140 nmol/L (5 µg/dL) with ACTH above 2 times the upper limit of normal: primary insufficiency is highly likely |
| Synthetic ACTH stimulation test | Injection, measurement at 30 or 60 min | Confirming a deficiency | Peak below 500 nmol/L (18 µg/dL): adrenal insufficiency |
| Late-night salivary cortisol | Saliva between 23:00 and midnight, on 2 evenings | Loss of the night-time trough | Normally below 145 ng/dL (4 nmol/L); sensitivity of 92 to 100% |
| Urinary free cortisol | 24-hour urine collection, at least 2 collections | Excessive total production | Compared with the laboratory reference range |
| Dexamethasone suppression test | 1 mg between 23:00 and midnight, blood sample between 8 am and 9 am | Cortisol that fails to suppress | Expected below 1.8 µg/dL (50 nmol/L) |
An abnormal result must be confirmed by a second test, with an endocrinologist’s advice. Conversely, a “slightly high” value on a stressful day or after a poor night’s sleep has no meaning in isolation.
Which everyday habits really affect cortisol?
Several habits change it measurably, but the effect is often modest and temporary.
- Sleep : in young men, one night of partial or total sleep deprivation increased the following evening’s cortisol by 37% and 45% respectively, and delayed its return to resting levels by at least an hour. To explore further: melatonin and sleep.
- Physical activity : in 12 active men, 30 minutes at 40% of maximal oxygen uptake (VO2max) did not significantly alter cortisol (+5.7%), compared with +39.9% at 60% and +83.1% at 80%. This exercise-related peak is temporary and normal.
- Caffeine : in 96 healthy young adults, it markedly raised cortisol after 5 days of abstinence. After 5 days of daily intake (300 or 600 mg per day), the response to the morning dose disappeared, but a rise returned in the afternoon after a second dose.
- Alcohol : in a cross-sectional study of 3,670 middle-aged adults, each weekly unit was associated with around 3% higher salivary cortisol in men, and heavy drinkers had a flatter curve.
- Meditation : a meta-analysis of randomised trials found a moderate effect on blood cortisol (10 studies), only in patients with a physical illness; for salivary cortisol (21 studies), the effect was small and not significant.
Can food supplements affect cortisol?
It is necessary to distinguish what trials have measured from what a supplement may claim: none is authorised to present itself as lowering cortisol.
Ashwagandha. A 2025 meta-analysis (7 trials, 488 participants, at least 250 mg per day for at least 2 weeks) found cortisol levels 1.16 µg/dL lower than in control groups, with no significant effect on perceived stress. Another, in 2026 (23 trials, 1,706 people), also reported a difference, while highlighting the heterogeneity of the trials. Extracts, doses and populations vary, and the authors call for longer trials. This plant has no authorised health claim; its precautions are detailed in our article on ashwagandha and its studied effects, and another so-called “adaptogenic” plant is covered in our guide to rhodiola rosea: fatigue, stress, doses and precautions.
Vitamins and minerals. EU Regulation 432/2012 authorises certain claims relating to hormones, the nervous system or psychological functions for a product providing at least a significant amount of the nutrient. None mentions cortisol:
- “Pantothenic acid contributes to normal synthesis and metabolism of steroid hormones, vitamin D and some neurotransmitters”.
- “Vitamin B6 contributes to the regulation of hormonal activity”.
- “Magnesium contributes to normal psychological function”.
- “Vitamin C contributes to the normal functioning of the nervous system”.
For forms and intakes, see our comparison of magnesium forms and our article on vitamin B6.
Frequently asked questions
What is the difference between cortisol and cortisone?
Cortisol is the active form, cortisone its inactive form. The enzyme 11β-HSD2 inactivates cortisol into cortisone; 11β-HSD1 regenerates it in the liver, fat tissue and brain. In everyday language, “cortisone” also refers to prescribed corticosteroids.
Does cortisol explain waking up at 3 am?
Its rise does start at around 3–4 am, but in everyone, including people who sleep through the night. Repeated night-time waking has many possible causes and deserves medical advice if it persists.
Do you need to fast for an 8 am cortisol blood test?
The key factors are the time, aligned with the expected peak, and avoiding unusual exertion or stress just beforehand. For fasting, follow the laboratory’s instructions and report your treatments, particularly corticosteroids and oral contraception.
Are salivary cortisol tests sold online reliable?
Salivary cortisol is a genuine test, but it follows a defined protocol: collection between 23:00 and midnight, on two evenings, using a validated method. Smoking, corticosteroid cream, shift work or jet lag can distort the result. Outside this setting, an isolated number allows no conclusion.
Is cortisol different in women?
Oral oestrogens increase the protein that carries cortisol: total blood cortisol appears higher, while urinary free cortisol remains normal. Pregnancy also physiologically raises cortisol. The doctor needs to know this when interpreting a test.
Which food lowers cortisol?
None, in the sense of a proven effect. “Anti-cortisol” drinks are not backed by trials measuring cortisol. Limiting alcohol, avoiding excessive caffeine and eating a varied diet remain reasonable guidelines.
Conclusion
Cortisol is not an enemy: it is a vital, rhythmic hormone that legitimately rises in response to demands. Genuine excesses and deficiencies are rare and are diagnosed through tests selected, repeated and interpreted by a doctor. Sleep, appropriate physical activity, and reasonable caffeine and alcohol intake shape its curve in modest but real ways. Rather than trying to “lower” it, it is better to preserve a regular rhythm.
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- Bornstein SR, Allolio B, Arlt W, et al. Diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2016;101(2):364-389. https://doi.org/10.1210/jc.2015-1710
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- Lovallo WR, Whitsett TL, al'Absi M, et al. Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels. Psychosom Med. 2005;67(5):734-739. https://doi.org/10.1097/01.psy.0000181270.20036.06
- Badrick E, Bobak M, Britton A, et al. The relationship between alcohol consumption and cortisol secretion in an aging cohort. J Clin Endocrinol Metab. 2008;93(3):750-757. https://doi.org/10.1210/jc.2007-0737
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- Albalawi AA. Dual impact of Ashwagandha: significant cortisol reduction but no effects on perceived stress. A systematic review and meta-analysis. Nutr Health. 2025;31:1395-1408. https://doi.org/10.1177/02601060251363647
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- Règlement (UE) n° 432/2012 de la Commission du 16 mai 2012 établissant une liste des allégations de santé autorisées portant sur les denrées alimentaires. Journal officiel de l'Union européenne, L 136 du 25.5.2012. https://eur-lex.europa.eu/eli/reg/2012/432/oj/fra
Food supplements do not replace a varied, balanced diet or a healthy lifestyle. Ask a healthcare professional for advice if you take medication, are pregnant or are breastfeeding.
