Low cortisol: the under-discussed side

Cortisol is often described as the body's stress hormone, but its role is much broader than that. It helps regulate blood sugar, blood pressure, metabolism and the body's response to physical stress. It also follows a natural daily rhythm, with levels normally highest around the morning and gradually falling throughout the day.

This means that cortisol results need to be interpreted in context. A lower cortisol reading doesn't necessarily mean there is a problem, and feeling tired in the morning doesn't automatically mean your cortisol is low.

However, persistently low cortisol can be a sign of a problem with the adrenal glands or the system that controls them. Understanding the difference can help you make sense of cortisol testing and know when to seek medical advice.

What does cortisol do?

Cortisol is a steroid hormone made by the adrenal glands, which sit above your kidneys.

It has several important roles in the body. Cortisol helps:

• Regulate blood sugar and how your body uses energy
• Maintain blood pressure
• Support the body's response to illness, injury and other physical stress
• Regulate aspects of the immune system
• Follow the body's sleep-wake cycle

Cortisol levels aren't constant. They normally change throughout the day, with levels generally higher in the morning and lower later in the day.

This daily pattern is known as the circadian rhythm. The rise and fall in cortisol is one part of the wider process that helps your body adjust between sleep and being awake.

What does low cortisol mean?

A low cortisol result can mean different things depending on when the sample was taken, how it was measured and what is happening with your health.

For example, cortisol naturally falls throughout the day, so a result that is appropriate for the evening could be considered low if it were measured first thing in the morning.

A single cortisol result also cannot tell you everything about how your cortisol behaves across the day.

Low cortisol and a blunted cortisol awakening response aren't quite the same thing. The cortisol awakening response describes the natural rise in cortisol shortly after you wake up. A genuinely low cortisol level can have different causes, including problems with the adrenal glands or the systems that control cortisol production.

If your symptoms suggest that your cortisol may be too low, your healthcare professional can arrange the appropriate tests. An early-morning cortisol blood test is usually used because cortisol levels naturally change throughout the day. A random cortisol test isn't usually suitable for investigating suspected adrenal insufficiency, unless someone is acutely unwell and an adrenal crisis is suspected.

What is the cortisol awakening response?

Cortisol normally begins to rise around the time you wake up. This is sometimes called the cortisol awakening response.

The response is part of the body's normal transition from sleep to daytime activity. Cortisol helps make energy available and supports alertness and other functions as you become active.

The size of this response varies between people and can also be affected by sleep, stress, illness, medication and other factors.

Research has explored whether a weaker or altered cortisol awakening response is associated with fatigue, sleepiness and other health measures. However, this doesn't mean that a low morning cortisol response is the direct cause of morning tiredness or brain fog.

If you're regularly struggling to wake up, feel exhausted despite getting enough sleep or have unexplained fatigue, there are many possible causes worth discussing with a healthcare professional.

What can cause genuinely low cortisol?

Persistently low cortisol can occur when the adrenal glands don't produce enough cortisol, known as adrenal insufficiency.

There are several possible causes, such as:

Problems with the adrenal glands

Addison's disease is a rare form of primary adrenal insufficiency in which the adrenal glands don't produce enough cortisol and, often, aldosterone.

It can cause symptoms including extreme tiredness, muscle weakness, loss of appetite, unintentional weight loss, dizziness and low blood pressure. Some people also develop darker areas of skin or a craving for salty foods.

Problems with the pituitary gland

The pituitary gland helps control the adrenal glands by producing a hormone called ACTH. If the pituitary gland isn't producing enough ACTH, the adrenal glands may not receive the signal they need to produce cortisol.

This is known as secondary adrenal insufficiency.

Long-term steroid treatment

Taking corticosteroid medicines for a long time can suppress the body's own cortisol production. This can sometimes lead to adrenal insufficiency when the medication is reduced or stopped.

This is why prescribed steroids should not be stopped suddenly without medical advice. The dose may need to be reduced gradually under the supervision of a healthcare professional.

What are the symptoms of low cortisol?

Symptoms of cortisol deficiency can develop gradually and are often similar to those caused by other conditions.

Possible symptoms include:

• Persistent or extreme tiredness
• Muscle weakness
• Dizziness or light-headedness, particularly when standing
• Low blood pressure
• Loss of appetite
• Unintentional weight loss
• Nausea, vomiting or abdominal pain
• Difficulty concentrating
• Craving salty foods
• Changes in skin colour in some people

Having one or more of these symptoms doesn't mean you have low cortisol or adrenal insufficiency. They can have many other causes.

If symptoms are persistent, unexplained or getting worse, speak to your GP so they can decide whether further investigation is appropriate.

Does feeling tired in the morning mean your cortisol is low?

Not necessarily. Morning tiredness can happen for many reasons, including insufficient sleep, an irregular sleep schedule, sleep disorders, stress, medication and a range of physical or mental health conditions.

Cortisol does normally rise around waking, but there isn't enough evidence to say that ordinary morning sluggishness means your cortisol awakening response is too low.

If you're regularly relying on caffeine to function in the morning or feel unable to wake properly despite getting enough sleep, it's worth looking at your sleep and wider health rather than assuming cortisol is the cause.

Can stress affect cortisol levels?

Yes. Cortisol is part of the body's response to stress, and acute stress can temporarily change cortisol levels.

Sleep disruption, changes to your daily routine, illness, some medicines and other factors can also affect cortisol measurements.

Long-term stress is more complicated. It doesn't simply mean that your cortisol will stay high or eventually become "burnt out". Research into chronic stress and changes in cortisol patterns is ongoing, and individual responses vary.

This is one reason why a single cortisol measurement can be difficult to interpret on its own.

Why does the time of day matter?

If low cortisol is a concern, the timing of the test matters. An early-morning cortisol blood test is usually taken between 8am and 9am, when cortisol levels are naturally at their highest. A random cortisol test isn't usually suitable because levels change throughout the day.

Other types of cortisol testing may be designed to look at the daily pattern rather than assess adrenal insufficiency. Saliva can be used to measure cortisol at different points throughout the day, allowing changes in the daily pattern to be assessed.

This means you shouldn't compare a morning result directly with an afternoon or evening result without knowing how the test is intended to be interpreted.

What is a cortisol profile?

Rather than looking at one cortisol measurement, a cortisol profile takes several samples at different points in the day.

This can show how your cortisol changes from morning through to evening and may provide more information about your daily cortisol rhythm than a single measurement.

Bluecrest's cortisol stress test uses multiple saliva samples collected across the day to map this pattern.

Bluecrest describes the purpose of this type of testing as looking at the daily cortisol rhythm rather than relying on a single reading.

It's important to distinguish this from the clinical investigation of adrenal insufficiency. A cortisol profile is not a substitute for the medical tests used to diagnose conditions such as Addison's disease.

What can affect a cortisol test result?

Several factors can influence cortisol levels or the way a result should be interpreted.

These can include:

• The time of day the sample was taken
• Sleep patterns and disrupted sleep
• Acute illness or physical stress
• Psychological stress
• Some medicines, including steroid medicines
• Hormone treatments such as some forms of oestrogen
• The type of sample and testing method used

This is another reason not to interpret a cortisol result without considering how and when it was measured.

What can you do to support a healthy cortisol rhythm?

You don't need to follow a strict morning routine to "fix" your cortisol.

However, habits that support a regular sleep-wake rhythm are generally good for your health and can help keep your body clock consistent.

These include:

Keep your sleep schedule reasonably consistent

Going to bed and waking at similar times each day can help support your body's circadian rhythm. Most adults need around seven to nine hours of sleep, although individual requirements vary.

Get some daylight during the day

Natural light is an important signal for your body clock. Getting outside during the day, particularly earlier in the day, can help reinforce your sleep-wake rhythm.

Stay physically active

Regular physical activity supports sleep and overall health. The NHS recommends that adults aim for at least 150 minutes of moderate activity each week, alongside strengthening activities on at least two days a week.

Don't rely on caffeine to compensate for poor sleep

Caffeine can temporarily increase alertness, but using increasing amounts to compensate for ongoing tiredness doesn't address the reason you're feeling tired. If you're regularly exhausted despite getting enough sleep, it's worth discussing this with a healthcare professional rather than assuming you need more caffeine or that your cortisol is low.

When should you speak to a GP about low cortisol?

If you're experiencing persistent unexplained fatigue alongside symptoms such as weight loss, loss of appetite, dizziness, low blood pressure, nausea, vomiting or muscle weakness, speak to a GP.

These symptoms can have many possible causes, but they can also occur with adrenal insufficiency and may need investigation.

If you have known adrenal insufficiency and develop severe vomiting, dehydration, very low blood pressure, confusion, fainting or a sudden and significant deterioration, this can be an adrenal crisis and needs urgent medical attention.

Understand your cortisol pattern with Bluecrest Wellness

If you'd like to understand more about how your cortisol levels change throughout the day, Bluecrest's Cortisol Stress Test uses multiple saliva samples to create a profile of your daily cortisol pattern.

Looking at several samples can provide more context than a single cortisol reading, helping you see how your levels change from morning through to evening.

Explore the Cortisol Stress Test.

Need help? Call free on 0800 652 2183 to speak to one of our team.

This article is for general health information purposes and does not constitute medical advice. A Bluecrest Cortisol Stress Test is not intended to diagnose adrenal insufficiency. If you have persistent or concerning symptoms, speak to your GP or another healthcare professional.