What Is Cortisol? How the Stress Hormone Affects Your Health

You've probably heard people blame high cortisol for stubborn belly fat, burnout, poor sleep, anxiety, and weight gain. But is it really the problem?

Cortisol is a steroid hormone produced by your adrenal glands. Although it's often called the body's stress hormone, it does much more than help your body respond to stress. 

It regulates your metabolism, blood sugar, blood pressure, inflammation, and sleep-wake cycle, making it essential for everyday health. Problems usually arise when cortisol levels remain too high or too low for long periods.

So, what causes cortisol levels to become too high or too low? Can they make losing weight harder? And when should you see a doctor? 

Here's everything you need to know.

TL;DR: What Is Cortisol?

• Cortisol is a steroid hormone produced by the adrenal glands that regulates your metabolism, blood sugar, blood pressure, inflammation, sleep-wake cycle, and response to stress.

• Cortisol levels naturally rise in the morning and fall at night. Doctors can measure them using blood, saliva, urine, or ACTH tests.

• High cortisol levels may result from chronic stress, long-term corticosteroid use, or conditions such as Cushing syndrome, while low cortisol levels may be caused by Addison's disease or pituitary disorders.

• Persistently high or low cortisol levels can cause symptoms such as fatigue, weight changes, poor sleep, dizziness, muscle weakness, and mood changes.

• Cortisol isn't bad. It's an essential hormone, and health problems usually occur only when cortisol levels remain too high or too low for long periods.

• Supporting healthy cortisol levels starts with quality sleep, stress management, regular exercise, a balanced diet, and seeking medical advice if symptoms persist.

Where Is Cortisol Produced in the Body?

Cortisol is produced by your adrenal glands, two small, triangular-shaped glands that sit on top of each kidney.

More specifically, it's made in the adrenal cortex, the outer layer of each adrenal gland.

While the adrenal glands produce cortisol, they don't decide when to release it. That process is controlled by your brain through a communication network known as the hypothalamic-pituitary-adrenal (HPA) axis.

What Is the Adrenal Cortex?

The adrenal glands have two main parts:

• The adrenal cortex (outer layer): Produces steroid hormones, including cortisol, aldosterone, and small amounts of sex hormones.

• The adrenal medulla (inner layer): Produces adrenaline (epinephrine) and noradrenaline (norepinephrine), hormones that trigger your body's immediate fight-or-flight response.

Although both parts help your body respond to stress, they produce different hormones that perform different jobs.

How Does the Brain Control Cortisol Production?

Your brain and adrenal glands work together through the hypothalamic-pituitary-adrenal (HPA) axis, a communication system that regulates how much cortisol your body makes.

Here's how it works:

1. The hypothalamus detects physical or emotional stress and sends a signal to the pituitary gland.

2. The pituitary gland releases adrenocorticotropic hormone (ACTH) into your bloodstream.

3. ACTH travels to the adrenal glands, stimulating the adrenal cortex to produce and release cortisol.

4. Once enough cortisol is circulating, it signals the hypothalamus and pituitary gland to reduce ACTH production, preventing your body from making more cortisol than it needs.

Think of the HPA axis as your body's thermostat.

When cortisol levels fall, the brain tells your adrenal glands to produce more. When levels rise high enough, it tells them to slow down.

This feedback loop helps keep cortisol within a healthy range under normal circumstances.

When this system becomes disrupted by chronic stress, certain medications, or medical conditions such as Cushing syndrome, cortisol production can become too high or too low, leading to symptoms that affect your health.

What Does Cortisol Do in the Body?

Cortisol helps regulate many of the processes your body depends on every day.

Beyond helping you respond to stress, it supports your metabolism, keeps your blood sugar stable, maintains healthy blood pressure, regulates inflammation, and follows a natural daily rhythm that helps you wake up in the morning and wind down at night.

These functions are why cortisol is often called an essential hormone rather than simply a stress hormone.

Every day, your body carefully adjusts cortisol levels to match its needs. For example, levels naturally rise before you wake up to help you feel alert and gradually fall throughout the day as your body prepares for sleep.

Most people don't notice cortisol working because it's constantly operating behind the scenes.

It's only when cortisol levels remain unusually high or low for long periods that problems such as fatigue, weight changes, poor sleep, mood disturbances, or other health issues may begin to develop.

What Are Cortisol Levels?

Cortisol levels refer to the amount of cortisol circulating in your body at a given time.

They naturally rise and fall throughout the day in a pattern known as the circadian rhythm and can be measured using blood, saliva, or urine tests.

Healthy cortisol levels don't stay the same all day, so doctors interpret test results based on the type of test, the time it was taken, and your symptoms.

What Is a Normal Cortisol Level?

A normal cortisol level follows your body's natural sleep-wake cycle.

Levels are usually highest in the early morning, helping you wake up, feel alert, and prepare for the day ahead. They gradually decline throughout the day and are lowest late in the evening, allowing your body to relax and prepare for sleep.

Because of this daily rhythm, a cortisol level that's considered normal at 8 a.m. could be unusually high if measured late at night.

It's also important to know that there's no single "normal" cortisol number for everyone. Reference ranges vary depending on:

• The type of test (blood, saliva, or urine)

• The time of day the sample is collected

• The laboratory analysing the sample

• Your age, medical history, and any medications you're taking

For this reason, doctors don't diagnose a cortisol disorder based on a single number alone. They interpret your test results alongside your symptoms and, if needed, order additional tests.

What Is a High Cortisol Level?

A high cortisol level means your body is producing or being exposed to more cortisol than it needs over a prolonged period.

Temporary increases are completely normal during stressful situations, illness, or intense exercise. The concern is when cortisol remains persistently elevated without returning to its normal daily rhythm.

High cortisol levels may be caused by:

• Chronic stress

• Long-term use of corticosteroid medications

• Cushing syndrome

• Certain pituitary or adrenal gland disorders

Symptoms vary from person to person but may include:

• Weight gain, particularly around the abdomen

• Increased appetite and food cravings

• Difficulty sleeping

• Fatigue

• Mood changes such as anxiety or irritability

• High blood pressure

• Muscle weakness

One of the most well-known causes of persistently high cortisol is Cushing syndrome, a rare condition in which the body produces too much cortisol or is exposed to high doses of corticosteroid medication over a long period.

If you'd like to understand how chronically high cortisol can affect appetite, fat storage, and weight loss, read our guide on Why High Cortisol Levels Make Losing Weight Harder.

What Is a Low Cortisol Level?

A low cortisol level means your body isn't producing enough cortisol to meet its daily needs.

Although it's less common than high cortisol, it can become serious if left untreated because cortisol is essential for maintaining blood pressure, blood sugar, and your body's response to physical stress.

Low cortisol levels may occur because of:

• Addison's disease, where the adrenal glands are damaged and can't produce enough cortisol.

• Pituitary disorders that reduce the production of adrenocorticotropic hormone (ACTH), the hormone that signals the adrenal glands to make cortisol.

• Certain medications or medical treatments that affect adrenal function.

Common symptoms include:

• Persistent fatigue

• Dizziness, especially when standing up

• Unexplained weight loss

• Muscle weakness

• Low blood pressure

• Nausea or abdominal pain

If you experience these symptoms, especially alongside unexplained weight loss or frequent dizziness, it's important to see a healthcare professional for proper evaluation and testing.

How Are Cortisol Levels Tested?

Doctors don't diagnose high or low cortisol based on symptoms alone because fatigue, weight changes, poor sleep, and mood changes can have many different causes. If a cortisol disorder is suspected, they may recommend one or more tests to measure your cortisol levels and determine whether your adrenal glands and pituitary gland are working properly.

The type of test you need depends on your symptoms, the time of day, and the condition your doctor is investigating.

1. Blood Test

A blood test is one of the most common ways to measure cortisol levels. Because cortisol follows a natural daily rhythm, the sample is often collected early in the morning when levels are normally at their highest.

If your doctor suspects your cortisol rhythm is abnormal, they may also request an evening blood sample for comparison.

A blood test is commonly used to investigate:

• Suspected high or low cortisol levels

• Adrenal insufficiency

• Cushing syndrome

• Pituitary disorders

2. Saliva Test

A saliva test measures the amount of free cortisol in your saliva, usually late at night when cortisol levels should be at their lowest.

Unlike a blood test, saliva testing is non-invasive and can often be done at home. It's particularly useful when doctors suspect Cushing syndrome, as people with the condition often have abnormally high cortisol levels at night.

3. Urine Test

A 24-hour urine cortisol test measures the total amount of cortisol your body produces over an entire day.

Instead of capturing cortisol at a single moment, this test provides a more complete picture by collecting all urine passed over a 24-hour period. It's commonly used to help confirm persistently high cortisol levels and investigate conditions such as Cushing syndrome.

4. ACTH Test

If your cortisol level is abnormal, your doctor may order an adrenocorticotropic hormone (ACTH) test to help determine the underlying cause.

ACTH is a hormone produced by the pituitary gland that signals your adrenal glands to make cortisol.

By measuring both ACTH and cortisol together, doctors can often identify whether the problem originates in the:

• Adrenal glands, which produce cortisol, or

• Pituitary gland, which controls cortisol production through the HPA axis.

In some cases, additional tests such as imaging scans or stimulation tests may also be needed to confirm the diagnosis.

The important thing to remember is that no single cortisol test tells the whole story. Doctors interpret your symptoms, medical history, physical examination, and test results together before diagnosing conditions such as adrenal insufficiency or Cushing syndrome.

Cortisol vs Adrenaline: What's the Difference?

Cortisol and adrenaline are both stress hormones, but they don't do the same job. 

Adrenaline prepares your body to react to immediate danger within seconds, while cortisol provides a steadier supply of energy that helps you cope with stress over a longer period.

They work together, but they act at different times and have different effects on the body.

Imagine you're walking through a park and suddenly a dog starts chasing you.

Adrenaline is released first. Your heart beats faster, your breathing quickens, your pupils dilate, and your muscles receive more blood so you can react immediately.

Once the immediate danger has passed, cortisol helps your body recover by maintaining blood sugar, replacing the energy you used, and helping you cope with the physical and emotional stress of the experience.

Both hormones are essential for survival. Problems usually arise when cortisol remains elevated for long periods because of chronic stress or an underlying medical condition, whereas adrenaline is designed to rise and fall quickly in response to short-term situations.

Are Corticosteroids the Same as Cortisol?

No. Cortisol and corticosteroids are closely related, but they aren't the same thing.

Corticosteroids are medications designed to mimic the effects of cortisol. Doctors prescribe them to reduce inflammation and suppress an overactive immune system when treating conditions such as asthma, eczema, rheumatoid arthritis, inflammatory bowel disease, and severe allergies.

Although corticosteroids work like cortisol, they're manufactured drugs rather than hormones produced by your body.

Common corticosteroid medications include:

• Hydrocortisone

• Prednisone

• Prednisolone

• Dexamethasone

One important difference is that long-term use of corticosteroid medications can affect your body's natural cortisol production.

Because these medicines act like cortisol, your brain may reduce the amount of adrenocorticotropic hormone (ACTH) it sends to the adrenal glands.

Over time, this can cause the adrenal glands to produce less cortisol on their own.

For this reason, people who have taken corticosteroids for a long time are usually advised not to stop them suddenly.

Instead, their healthcare provider may gradually reduce the dose to give the adrenal glands time to resume normal cortisol production.

If you're taking corticosteroid medication and are concerned about how it may affect your cortisol levels, speak with your healthcare provider before making any changes to your treatment.

Common Myths About Cortisol

Social media has turned cortisol into the villain behind almost every health problem, from belly fat to burnout. 

While chronic cortisol imbalance can affect your health, many of the claims circulating online are oversimplified or simply untrue. Here are some of the most common myths.

Myth 1: Cortisol Is Always Bad

Cortisol is essential for life.

Your body needs cortisol to regulate metabolism, maintain blood sugar and blood pressure, control inflammation, and respond to physical and emotional stress. Without it, your body wouldn't function properly. The goal isn't to eliminate cortisol but to maintain healthy cortisol levels.

Myth 2: Belly Fat Always Means High Cortisol

Belly fat has many possible causes. Although chronically high cortisol may contribute to fat accumulating around the abdomen, it isn't the only explanation. 

Genetics, age, menopause, physical inactivity, poor sleep, excess calorie intake, and certain medical conditions can all influence where your body stores fat.

Myth 3: You Need a Cortisol Detox

There's no such thing as a cortisol detox. Despite what some wellness products claim, you can't flush cortisol out of your body with teas, juices, or supplements. 

If your cortisol levels are high, the solution is to identify and address the underlying cause, whether that's chronic stress, poor sleep, medication use, or a medical condition.

Myth 4: Supplements Alone Can Lower Cortisol

Supplements aren't a substitute for healthy habits. Some supplements, such as ashwagandha or magnesium, have shown promise in supporting healthy cortisol levels in certain people. 

However, they work best alongside stress management, quality sleep, regular exercise, and a balanced diet. No supplement can consistently lower cortisol if the underlying cause remains untreated.

Myth 5: Everyone Should Get Their Cortisol Tested

Most people don't need a cortisol test.

Doctors usually recommend cortisol testing only when someone has symptoms or signs that suggest a hormone disorder, such as unexplained weight changes, persistent fatigue, muscle weakness, low blood pressure, or features of Cushing syndrome or Addison's disease. 

Testing without a medical reason can lead to confusing or misleading results because cortisol naturally changes throughout the day.

Myth 6: High Cortisol Is the Only Reason People Gain Weight

Weight gain is usually caused by several factors working together.

High cortisol can increase appetite, affect sleep, and make it more difficult to maintain healthy habits, but it isn't the only factor that influences body weight. Diet, physical activity, genetics, age, medications, hormones, and underlying medical conditions all play important roles.

If you're struggling to lose weight despite eating well and exercising regularly, it's worth speaking with a healthcare professional to identify the underlying cause rather than assuming cortisol is solely to blame.

Frequently Asked Questions About Cortisol

Is cortisol good or bad?

Neither. Cortisol is essential for life and plays an important role in regulating your metabolism, blood sugar, blood pressure, inflammation, and your body's response to stress. 

Problems usually arise only when cortisol levels remain too high or too low for long periods.

Can stress permanently increase cortisol?

Not usually. Cortisol naturally rises during stressful situations and falls once the stress has passed. 

However, ongoing stress, poor sleep, certain medications, or medical conditions can keep cortisol levels elevated for longer than normal. 

Addressing the underlying cause can often help restore a healthy cortisol rhythm.

Does high cortisol always cause weight gain?

No. While persistently high cortisol can increase appetite, disrupt sleep, and contribute to weight gain in some people, it's only one of many factors that affect body weight. 

Diet, physical activity, genetics, age, medications, and underlying health conditions also play important roles.

What foods help lower cortisol?

No single food can lower cortisol on its own. 

However, eating a balanced diet rich in vegetables, fruits, whole grains, lean protein, healthy fats, and fibre supports overall health and may help your body regulate cortisol more effectively. 

Limiting excessive alcohol and highly processed foods may also be beneficial.

Can exercise lower cortisol?

Yes, regular exercise can help your body become more resilient to stress over time. 

Although cortisol naturally increases during physical activity, it usually returns to normal afterwards. Moderate exercise combined with adequate recovery is generally more beneficial than overtraining.

Can you test your cortisol levels at home?

Some home saliva test kits are available, but they aren't suitable for diagnosing cortisol disorders on their own.

If you have symptoms of persistently high or low cortisol, it's best to speak with a healthcare professional, who can recommend the most appropriate tests and interpret the results in the context of your symptoms and medical history.

Can high cortisol be treated?

Yes. Treatment depends on the underlying cause. If high cortisol is linked to chronic stress or lifestyle factors, improving sleep, managing stress, exercising regularly, and eating a balanced diet may help. 

If it's caused by a medical condition such as Cushing syndrome or long-term corticosteroid use, treatment may involve medication, surgery, or adjusting your current treatment under medical supervision.

Can You Lower Cortisol Naturally?

Yes, but the goal is to support healthy cortisol levels by addressing the habits and lifestyle factors that influence how your body responds to stress. 

Many people can support healthy cortisol regulation through healthy daily habits.

Getting seven to nine hours of quality sleep each night helps maintain your body's natural cortisol rhythm, while managing chronic stress through techniques such as meditation, deep breathing, or spending time outdoors can reduce the impact of long-term stress. 

Regular exercise also helps your body become more resilient to stress, provided you allow enough time for recovery and avoid overtraining. 

A balanced diet rich in lean protein, vegetables, fruits, whole grains, healthy fats, and fibre supports your overall health and helps keep your energy levels stable.

If you've made healthy lifestyle changes but still have symptoms of persistently high or low cortisol, such as unexplained weight changes, ongoing fatigue, muscle weakness, or low blood pressure, it's important to speak with a healthcare professional. 

They can determine whether further testing is needed and recommend the most appropriate treatment for the underlying cause.