Cortisol: Everything You Need to Know About the 'Stress Hormone'

Sometimes called “the stress hormone,” cortisol plays a role in many diseases and conditions.

Cortisol is a steroid hormone that helps the body respond to stress. It’s sometimes called the “stress hormone.” That’s because levels of cortisol in the body spike during times of high stress. (1)

Steroid hormones are a category of hormones synthesized naturally in the body from cholesterol. Collectively, they carry out a wide range of functions in the body.

Cortisol and Metabolism: What to Know

Cortisol, specifically, plays a role in metabolism. It stimulates the liver to increase production of blood sugar. It also helps the body convert fats, proteins, and carbohydrates into usable energy. As part of the body’s fight-or-flight response, cortisol is released during stressful times to give your body a natural energy boost. (2) This boost is meant to fuel your muscles to respond to a threatening situation. But when cortisol levels are constantly high, due to chronic stress, these same effects may result in insulin resistance and type 2 diabetes. (2)

Cortisol also helps the body fight inflammation, control the balance of salt and water in the body, and regulate blood pressure. (1)

This hormone is produced by the adrenal glands, two small, triangular-shaped glands that sit one on top of each kidney. From the adrenal glands, cortisol can be released directly into the bloodstream. (3)

The pituitary gland (a pea-sized gland at the base of the brain) and hypothalamus (a region of the brain that controls the activity of the pituitary gland) can sense whether the blood has the right amount of cortisol in it. These two brain regions work together to direct the adrenal glands to produce more or less cortisol, in essence acting as the control mechanism regarding how much cortisol is made. (3)

This connection between the hypothalamus, pituitary gland, and adrenal glands forms the backbone of the body’s stress response system.

Cortisol Levels: What Do They Mean?

Levels of the hormone cortisol rise and fall naturally throughout the day.

Cortisol levels reach their lowest levels late at night — usually around midnight. From there, levels begin to rise. Cortisol reaches its highest level in the body early in the morning, peaking around 9 a.m., before beginning to decline again throughout the later day. (4)

The pattern can change or become altered if people work irregular shifts or sleep a lot during the day. Diseases, including adrenal gland disorders, that affect the production or use of cortisol also can disrupt the normal pattern.

Adrenal gland disorders may arise when the adrenal glands produce too much or too little cortisol.

In Cushing's syndrome, there’s too much cortisol production, (5) while adrenal insufficiency (AI) is marked by too little cortisol production. (6)

Cushing's Syndrome and Cortisol: What to Know

Cushing's syndrome happens when there is too much cortisol in the blood for a prolonged period of time. This can cause physical and mental changes.

Cushing's syndrome symptoms may include: (5)

• Weight gain
• High blood pressure
• High blood sugar
• Muscle loss and weakness
• Swelling of the face
• Depression
• Skin that bruises easily
• Problems thinking clearly

The most common cause of Cushing's syndrome is taking steroid-type drugs, such as prednisone, which are structurally very similar to cortisol. This type of Cushing's syndrome typically goes away after medication is stopped. (5)

Cushing's syndrome also can be caused by a small tumor on the pituitary gland. (5)

Adrenal Insufficiency and Cortisol: What to Know

Adrenal insufficiency happens when the adrenal glands don’t make enough cortisol. This can happen when the adrenal glands do not work properly (Addison’s disease) or when the pituitary gland doesn’t direct the adrenal glands to make cortisol. (6)

Symptoms of adrenal insufficiency can include: (6)

• Severe fatigue and weakness
• Weight loss
• Faintness or dizziness, especially upon standing
• Low blood pressure
• Low blood sugar
• Darkened skin on the face, neck, and back of hands

People with adrenal insufficiency may need to take a type of steroid hormone medication, called glucocorticoids, to raise their cortisol levels. (6)

Testing Cortisol Levels

Your healthcare provider may recommend having your cortisol levels tested if he or she suspects you may have too little or too much cortisol production. (4)

Cortisol levels can be measured in blood, urine, or saliva.

Blood samples may be taken from a vein in the arm in the morning, when levels are highest.

Samples may also be taken around 4 in the afternoon, when levels should be considerably lower.

The blood test for a low cortisol is done by measuring levels in the blood both before and an hour after the injection of a drug called adrenocorticotropic hormone (ACTH). ACTH is a pituitary gland hormone that helps to stimulate cortisol production. In patients with a low cortisol level caused by Addison’s disease, the levels won’t rise even after injection of ACTH, whereas in normal persons the levels rise considerably.

Saliva also may be collected. During a saliva cortisol test, you will be asked to insert a swab into your mouth and wait a few minutes until it is saturated with saliva.

For a cortisol urine test, you may be asked to collect all the urine you produce over a 24-hour period in a container provided by the laboratory. But urinary cortisol levels can sometimes be tested with a single sample of the first urine in the morning.

Adrenal Fatigue and Cortisol

The term “adrenal fatigue” in recent years has been used in the media — and by some healthcare practitioners — to describe a host of vague symptoms, including tiredness, body aches, nervousness, and sleep and digestive problems. (7) The general idea is that constant stress may cause the cortisol-producing adrenal glands to “burn out” and stop producing their important hormones.

There’s no scientific evidence that adrenal fatigue exists. (8) The idea that stress causes the adrenal glands to “burn out” and stop making cortisol is not consistent with scientific understanding of how the adrenal glands work. Stress actually increases cortisol production. (9)

Neither the Endocrine Society — the world’s largest organization of hormone disorder doctors — nor any other major medical organization recognizes adrenal fatigue as a legitimate medical diagnosis. (9)

Cortisol, Metabolism, and Weight Gain

There’s been a lot of research linking chronic stress to weight gain and obesity in recent decades. (10) Cortisol — released from the adrenal glands into the bloodstream during stressful situations — plays an important role in metabolism, leading researchers to hypothesize that constantly high levels of cortisol may play a role in weight gain.

Some animal studies have shown that too much cortisol can promote the accumulation of belly fat. And researchers know that humans and lab animals tend to opt for energy-dense foods when under constant stress, leading some to suggest that chronically high cortisol levels also may play a role in making us crave high-calorie comfort foods. (10)

But scientific studies in humans have turned up mixed results on the relationship between high cortisol and weight gain, with some studies finding a link and others not. (11) A comprehensive review of scientific and medical studies, published in October 2012 in the journal Obesity, found no consistent relationship between cortisol levels and belly fat. (11)

Many of these older studies measured cortisol levels in blood, urine, or saliva. While these bodily fluids can serve as good markers for daily fluctuations in cortisol levels and help doctors assess when too much or too little cortisol is being produced, some scientists have argued that they may not provide the most accurate picture of long-term cortisol exposure. (10)

In a large study of more than 2,500 British adults, researchers measured cortisol concentrations in hair. They found that people with higher hair cortisol levels over a four year period were more likely to be obese — and to stay obese — than people with lower levels. The researchers, who published their study in February 2017 in the journal Obesity, said that hair cortisol may be a better marker of long-term cortisol exposure — and chronic stress — than cortisol levels measured in blood, urine, or saliva. (10)