Cortisol and the glucocorticoids

On this page

1. What is cortisol?
2. Where is cortisol produced?
3. Function of cortisol
4. The three phases of the stress response
5. Cortisol and fertility
6. Normal cortisol levels
7. Causes of high cortisol
8. Causes of low cortisol
9. When and how to test cortisol
10. Cortisol Awakening Response (CAR) — wired but tired
11. Cortisol in traditional Chinese medicine
12. Acupuncture and cortisol
13. Chinese herbal medicine and cortisol
14. Diet and lifestyle
15. My Fertility Guide
16. Related pages

1. What is cortisol?

Cortisol is the body's primary stress hormone and the most important of the glucocorticoids — a group that also includes corticosterone and cortisone. Cortisol is produced by the adrenal glands in response to stress (physical, psychological or metabolic) and follows a strong daily rhythm — high in the morning to wake us up, gradually falling through the day, and lowest around midnight.

While short bursts of cortisol are essential for survival and good health, chronically elevated cortisol — the kind produced by ongoing stress — has profound effects on fertility and almost every other body system.

Reference ranges vary from country to country and between laboratories. Always interpret your own result against the reference range provided by the laboratory that performed your test.

2. Where is cortisol produced?

Cortisol is produced by the cortex of the adrenal glands, which sit on top of each kidney. Its production is regulated by a feedback loop:

1. The hypothalamus releases corticotrophin-releasing hormone (CRH).
2. CRH stimulates the pituitary to release adrenocorticotrophic hormone (ACTH).
3. ACTH stimulates the adrenal cortex to produce cortisol.
4. Cortisol then negatively feeds back on both the hypothalamus and pituitary to switch the system off — unless ongoing stress overrides this.

3. Function of cortisol

Cortisol has many functions:

1. Mobilising glucose and fatty acids for energy in response to stress.
2. Suppressing inflammation and immune function — useful in acute injury, harmful when chronic.
3. Regulating blood pressure.
4. Maintaining the daily wake-sleep rhythm.
5. Modulating mood, alertness and cognitive function.

4. The three phases of the stress response

The body's response to stress occurs in three phases:

1. Alarm phase (level 1) — short-lived "fight or flight" response with adrenaline and a brief cortisol rise.
2. Resistance phase (level 2) — sustained, chronic elevation of cortisol when stress lasts more than a few hours. Most people in modern life live in this phase. Energy, lipid and protein reserves are depleted, fertility hormones become irregular, and leptin signalling is impaired.
3. Exhaustion phase (level 3) — when chronic stress finally exhausts the adrenals, cortisol may fall (so-called "adrenal fatigue") and the person experiences profound exhaustion, low mood and immune dysfunction.

5. Cortisol and fertility

Chronically elevated cortisol affects fertility in several ways:

1. Suppresses GnRH, leading to irregular cycles and anovulation.
2. Diverts pregnenolone (the precursor of both cortisol and progesterone) towards cortisol production — the "pregnenolone steal" — leading to low progesterone.
3. Reduces TH2 immune cells needed for embryo implantation.
4. Reduces ovarian and uterine blood flow.
5. Worsens insulin resistance, exacerbating PCOS.
6. Reduces oxytocin, the bonding hormone.

Research has shown that women starting fertility treatment with elevated cortisol have lower success rates. Reducing cortisol is therefore one of the most important fertility-supportive interventions.

6. Normal cortisol levels

Typical reference ranges for serum cortisol are approximately:

1. Morning (8–9 a.m.): 140–700 nmol/L (5–25 µg/dL).
2. Evening (4–5 p.m.): 80–300 nmol/L.
3. Late evening (11 p.m.): <100 nmol/L.

Reference ranges vary from country to country and between laboratories.

7. Causes of high cortisol

High cortisol is caused by:

1. Chronic psychological stress — the most common cause.
2. Sleep deprivation and shift work.
3. Excessive endurance exercise.
4. Chronic dieting and undereating.
5. Chronic illness or pain.
6. High caffeine and alcohol intake.
7. Cushing's syndrome (rare).
8. Synthetic glucocorticoid medications — prednisolone, dexamethasone etc.

8. Causes of low cortisol

Low cortisol is less common and is seen in:

1. Adrenal insufficiency (Addison's disease) — primary adrenal failure.
2. Pituitary insufficiency — secondary adrenal failure.
3. Long-term suppression by exogenous steroids.
4. Chronic exhaustion phase of the stress response.

9. When and how to test cortisol

Serum cortisol is usually measured in the morning (between 8–9 a.m.) when levels are at their peak. Salivary cortisol provides a more accessible way to measure cortisol multiple times across the day, capturing the daily rhythm. 24-hour urine cortisol gives a measure of total daily cortisol production. Hair cortisol, used in research, gives a measure of cortisol over the past 1–3 months.

Reference ranges vary from country to country. Always interpret your own result against the laboratory's reference range and discuss it with your doctor.

10. Cortisol Awakening Response (CAR) — what "wired but tired" actually measures

A single morning cortisol reading gives a snapshot; the Cortisol Awakening Response (CAR) gives the dynamics. In a healthy stress-response system, cortisol should rise sharply in the first 30–45 minutes after waking — typically by 50–75% above the waking level — producing the physiological "wake-up" that gets us out of bed. This response is one of the most consistent findings in stress-and-cortisol research and it is what saliva-based four-point testing measures. Testing kits ask you to spit into a small tube on waking, then again at 30 minutes, 60 minutes, and later in the day, so that the shape of the rise (not just the level) can be measured.

What CAR tells you that a single blood test does not

Two patients with the same 9am serum cortisol can have very different CARs. Meaningful patterns include:

• Blunted (flat) CAR — the classic "wired but tired" picture. Waking cortisol is normal or high, but the expected 30-minute peak barely occurs. Patients wake feeling exhausted and un-refreshed but paradoxically anxious and can't relax; sleep is broken; energy is uneven through the day; caffeine feels essential to function. Consistently seen in long-standing burnout, chronic fatigue syndrome, PTSD, post-COVID fatigue and long-term high-stress work.
• Exaggerated (spiky) CAR. Waking cortisol shoots up steeply and overshoots. Patients wake in a hyperaroused state, hearts racing, often at 4–5am, with racing thoughts. Common in acute stress, anxiety disorders, perimenopause and hyperthyroid pictures.
• Delayed CAR. The rise occurs but 60–90 minutes late. Patients feel foggy for the first two hours of the morning and only reach clarity mid-morning — a picture common in shift workers and long-standing chronic sleep restriction.
• Elevated evening cortisol. Cortisol should be at its lowest at midnight. When evening cortisol stays elevated the classical "second wind" pattern appears — energetic at 10pm, unable to fall asleep before 1am, waking tired.

How CAR is tested in the UK

CAR is not a standard NHS test. In UK practice it is typically ordered through:

• DUTCH tests (Dried Urine Test for Comprehensive Hormones) — several UK integrative-medicine providers offer these, capturing the daily cortisol rhythm plus its metabolites.
• Four-point salivary cortisol panels — simpler kits offered by specialist labs, some available directly to patients.

Interpretation is not straightforward and CAR results are best read against symptoms rather than in isolation. A test showing a blunted CAR in someone feeling well needs less action than the same result in someone with disabling fatigue.

The TCM correlate

The "wired but tired" blunted-CAR picture maps closely onto the classical TCM pattern of Kidney Yin and Yang deficiency with Heart-Kidney disharmony. The morning rise fails because the deep constitutional resource (Kidney essence) that drives it is depleted; the paradoxical anxious activation reflects the empty-Fire pattern in which unmoored Yang flares upward without foundation. This is the terrain in which acupuncture and Kidney-restoring formulae are most useful — treatments that steadily rebuild the foundation over three to six months tend to produce a gradual normalisation of both symptoms and, where re-tested, the CAR shape. Bolt-on stimulants (excess caffeine, high-dose adaptogens, aggressive exercise) all further deplete the same resource and prolong the problem.

For related material, see our posts on cortisol and stress, adrenal fatigue, and the general framework on sleep optimisation.

11. Cortisol in traditional Chinese medicine

In traditional Chinese medicine, the chronic elevation of cortisol from ongoing stress most closely matches the pattern of Liver Qi stagnation transforming into Heat, with consumption of Kidney Yin and eventually Kidney Yang. The exhaustion phase corresponds to severe Kidney Yang and Qi deficiency. Symptoms typically include irritability, tension headaches, irregular cycles, breast tenderness, sleep disturbance and eventually exhaustion.

12. Acupuncture and cortisol

Research has shown that acupuncture is highly effective at reducing cortisol levels by acting on the hypothalamic-pituitary-adrenal (HPA) axis. The deeply relaxing experience of acupuncture, the regulation of the autonomic nervous system, and the release of endorphins and oxytocin all contribute. Reducing cortisol with acupuncture is one of the major mechanisms by which it improves fertility outcomes — particularly in IVF.

13. Chinese herbal medicine and cortisol

Chinese herbal medicine has a rich tradition of formulae for stress-related disorders. The most commonly used is Xiao Yao San (Free and Easy Wanderer) and its modifications Jia Wei Xiao Yao San and Dan Zhi Xiao Yao San. Where stress has progressed to Kidney deficiency, formulae such as Liu Wei Di Huang Wan or You Gui Wan are added. Adaptogenic herbs including ginseng, rhodiola and ashwagandha (more commonly used in Ayurveda) can also be helpful.

14. Diet and lifestyle

To reduce chronically elevated cortisol:

1. Reduce psychological stress through mindfulness, meditation, yoga, t'ai chi, qi gong or counselling.
2. Sleep before 10 p.m. and aim for seven to eight hours per night.
3. Avoid excessive endurance exercise — three sessions of moderate cardio per week is sufficient.
4. Reduce caffeine — particularly after midday.
5. Limit alcohol.
6. Have fun! Watch comedies, spend time with friends, do things you enjoy.
7. Have regular acupuncture, massage or other relaxation-based therapies.
8. Avoid prolonged dieting and undereating, both of which raise cortisol.

15. My Fertility Guide

16. Related pages

• Fertility hormones directory
• Dehydroepiandrosterone (DHEA)
• Oxytocin
• Progesterone
• Prolactin
• Unexplained infertility
• Repeated IVF failure