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Cortisol (9am)

Cortisol, also known as ‘the stress hormone’, is crucial for regulating metabolism, controlling your sleep/wake cycle and much more.

Author: Leanne Edermaniger

April 24, 2024

Reviewed by: Dr Thom Phillips

In this article:

What is Cortisol?

Cortisol is a steroid hormone made from cholesterol. It influences many different functions within the body, including immunity and metabolism. Cortisol is also commonly called ‘the stress hormone’ because of its role in the body’s response to tense situations[1].

What Does Cortisol Do?

Cortisol is a glucocorticoid and is made in the adrenal glands, where it is then released into the blood and transported around the body. Almost all cells have cortisol receptors, so its action is dependent on which type of cell it is acting upon.

For example, cortisol may help control blood sugar levels, directly affecting metabolism[2], but it’s also associated with anti-inflammatory, immunosuppressive, and inflammatory-disease-regulating actions[3].

Some of cortisol’s other roles include:

  • Regulating blood pressure
  • Controlling the body’s sleep/wake cycle
  • Facilitating the use of carbohydrates, fats, and proteins for energy

Yet, cortisol is most synonymous with stress. During stressful periods, your body releases ‘fight or flight’ hormones, like adrenaline, to raise your heart and respiratory rate. In response, it then releases cortisol to help keep you on ‘high alert’, ready to attack or run away from the threat.

This heightened response has a high energy cost. So, cortisol also acts on your liver to release stored glucose, providing your body with a quick energy boost during times of stress.

What Are ‘Normal’ Cortisol Levels?

A healthy cortisol range for both males and females is 160-507nmol/L.

Based on data collected from Forth customers, we found that:

  • The overall average cortisol level is 370.1 nmol/L
  • The average level for men in the UK based on 2877 results is 380.1 nmol/L
  • The average level for women in the UK based on 2659 results is 360.9 nmol/L

Cortisol levels fluctuate throughout the day and in response to various stimuli, including intense exercise.

Because cortisol is involved in the sleep/wake cycle, in most people, cortisol levels are at their highest in the morning when they wake up. They then fall throughout the day, and are usually at their lowest at night, enabling better sleep.

However, in people who work night shifts, this pattern is reversed, suggesting a link with your daily routine. But cortisol is also released in response to intense exercise, which can be critical for energy metabolism during exercise and for recovery.

Therefore, it is important to test your cortisol levels at the right time of day to gain accurate results.

What Causes High Cortisol Levels?

Many factors contribute to high cortisol levels, including:

  • Stress. There are several types of stress, and your body can’t measure the severity of a situation, so even tiny, stressful episodes can be enough to raise your cortisol levels. Our data indicates that 25% of over 16s in the UK feel stressed every single day.
  • Anxiety. Feeling uneasy, worried, or fearful has also been linked to increased cortisol levels in adults, where levels increased by around nine times in stressful periods. Anxiety also increases cortisol in children[6].
  • Sleep. Cortisol levels naturally rise during the night. They begin to increase 2 to 3 hours after you go to sleep, continuing to rise into the morning and usually peaking at around 9 am. Cortisol levels naturally fall throughout the day, which is rapidly enhanced by sleep, and the cycle begins again[7].
  • Exercise. Moderate to high-intensity exercise increases circulating cortisol levels due to the increased physical stress placed on the body[8].
  • Contraceptive pill. Recent research shows that women who use hormonal contraceptives report more negative emotional responses to stress when cortisol levels rise[9]. Studies show that oral contraceptive pills blunt the cortisol reactivity compared to women who do not use hormonal birth control[10].
  • Cushing’s syndrome. A hormonal disorder caused by having high levels of cortisol for a long time.
  • Malnutrition. Severe malnutrition[11] and eating disorders, such as anorexia nervosa are linked to high cortisol levels[12].

Symptoms of High Cortisol

Prolonged high levels of cortisol can have damaging effects, so it is important to know the signs. Here are some of the most common high cortisol symptoms:

  • Rapid weight gain
  • Flushed, round face
  • High blood pressure (hypertension)
  • Muscle weakness
  • Mood changes
  • Frequent illness or infection
  • High blood sugar
  • Fatigue
  • Low sex drive
  • Slow wound healing
  • Bruising

As time goes on, high cortisol levels can increase your risk of complications, such as high cholesterol, high triglycerides, and high blood pressure, all of which are risk factors for heart disease[13], diabetes, poor mental health status, and menstrual cycle changes.

How to Lower Your Cortisol Levels

If you are experiencing high cortisol levels, how you reduce them will depend on what’s causing them to rise.

If high levels are caused by an underlying medical issue, like a pituitary gland or adrenal gland problem, or because you are taking medication like the oral contraceptive pill, you will need to consult your doctor for advice and to devise a plan.

If you experience high cortisol because of chronic or prolonged exposure to stress, there are several lifestyle changes you can make to naturally reduce your levels. They include:

  • Prioritise good, restful sleep
  • Practice mindfulness
  • Exercise regularly
  • Do something you enjoy every day
  • Laugh
  • Stay connected with friends and family
  • Look after a pet
  • Follow a healthy diet
  • Manage stress and recognise stressful thinking

What Causes Low Cortisol Levels?

Just like high levels, low cortisol levels are also not ideal and may be caused by issues with the hypothalamus, pituitary or adrenal glands.

A common cause is Addison’s disease, a rare but chronic illness caused by the adrenal glands not producing enough cortisol or aldosterone[14].

Taking corticosteroid medication for a long time can also disrupt the body’s natural cortisol production, especially when you stop taking it[15].

Symptoms of Low Cortisol Levels

Low cortisol symptoms often develop gradually and include:

  • Fatigue
  • Dizziness
  • Reduced muscle mass
  • Weight loss
  • Low blood pressure
  • Low blood sugar
  • Loss of appetite
  • Low mood
  • Dizziness or fainting
  • Cramps
  • Darkened skin, lips or gums[16]

How To Test Your Cortisol Levels at Home

If you’re concerned that you may be experiencing symptoms associated with high or low cortisol levels, then you can quickly and easily test yourself at home with our Cortisol Blood Test.

Because your cortisol levels naturally fluctuate throughout the day, it’s best to take the test before 10 am, or within 3 hours of waking if you’re an early riser or work nights.

We also check your cortisol levels as part of our:

Written by Leanne Edermaniger

Based in the UK, Leanne specialises in writing about health, medicine, nutrition, and fitness.

She has over 5 years of experience in writing about health and lifestyle and has a BSc (hons) Biomedical Science and an MSc Science, Communication and Society.

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Article references

  1. Hackney, A. C., & Walz, E. A. (2013). Hormonal adaptation and the stress of exercise training: the role of glucocorticoids. Trends in sport sciences, 20(4), 165–171.

  2. Dierckx, B. et al. (2012) ‘Persistence of anxiety disorders and concomitant changes in cortisol’, Journal of Anxiety Disorders, 26(6), pp. 635–641. doi:10.1016/j.janxdis.2012.04.001.

  3. Hirotsu, C., Tufik, S., & Andersen, M. L. (2015). Interactions between sleep, stress, and metabolism: From physiological to pathological conditions. Sleep science (Sao Paulo, Brazil), 8(3), 143–152. https://doi.org/10.1016/j.slsci.2015.09.002

  4. Manary, M. J., Muglia, L. J., Vogt, S. K., & Yarasheski, K. E. (2006). Cortisol and its action on the glucocorticoid receptor in malnutrition and acute infection. Metabolism: clinical and experimental, 55(4), 550–554. https://doi.org/10.1016/j.metabol.2005.11.009

  5. Schmalbach, I. et al. (2020) ‘Cortisol reactivity in patients with anorexia nervosa after stress induction’, Translational Psychiatry, 10(1). doi:10.1038/s41398-020-00955-7.

  6. Broersen, L.H. et al. (2015) ‘Adrenal insufficiency in corticosteroids use: Systematic review and meta-analysis’, The Journal of Clinical Endocrinology & Metabolism, 100(6), pp. 2171–2180. doi:10.1210/jc.2015-1218.

This article was written by Leanne Edermaniger

This information has been medically reviewed by Dr Thom Phillips

Thom works in NHS general practice and has a decade of experience working in both male and female elite sport. He has a background in exercise physiology and has published research into fatigue biomarkers.

Dr Thom Phillips

Dr Thom Phillips

Head of Clinical Services