You need rest. In fact, your survival literally depends on your ability to sleep.

Cortisol, the substance we associate with stress, has a powerful influence on sleep and waking in the human body.

Here’s what the research says about how cortisol interacts with your circadian rhythms and sleep cycles, and what you can do to lower your cortisol levels.

Cortisol is a hormone. It’s produced by a complex network known as the hypothalamic pituitary adrenal (HPA) axis.

The HPA axis includes your hypothalamus and pituitary gland, both of which are in your brain. It also includes your adrenal glands, which sit atop your kidneys.

To make cortisol, your hypothalamus sends a signal to your pituitary gland. It does this by releasing a substance called corticotropin-releasing hormone (CRH).

CRH stimulates your pituitary gland to send another hormone into your bloodstream. That hormone is called adrenocorticotropic hormone (ACTH).

ACTH travels through your bloodstream to your kidneys and cues the adrenal glands to produce cortisol. Once the adrenals have produced enough cortisol, the hypothalamus stops releasing CRH.

It’s a complex and sensitive feedback loop, and it has profound effects on your body, mind, and sleep.

Cortisol is best known for its role in the stress response. Under stressful circumstances, the HPA axis spurs the release of cortisol.

Cells all over your body are studded with cortisol receptors, so this hormone can trigger lots of nearly instant threat responses. These include:

  • rapid heart rate
  • spike in blood sugar
  • rapid breathing
  • sharpened senses

Cortisol prepares you to fight, to freeze, or run for your life. But that’s not all this powerful hormone does. It can also:

Sleep and the stress response share the same pathway: the HPA axis. When something disrupts the HPA axis functions, it can disrupt your sleep cycles as well.

Let’s look at how this can happen.

Circadian rhythm and cortisol

Your sleep-wake cycle follows a circadian rhythm. Every 24 hours, roughly synchronized with nighttime and daytime, your body enters a period of sleep followed by a waking period. The production of cortisol in your body follows a similar circadian rhythm.

Cortisol production drops to its lowest point around midnight. It peaks about an hour after you wake up. For many people, the peak is around 9 a.m.

In addition to the circadian cycle, around 15 to 18 smaller pulses of cortisol are released throughout the day and night. Some of those smaller bursts of cortisol correspond to shifts in your sleep cycles.

Cortisol and sleep cycles

Sleep isn’t a steady state. Your body goes through various stages of sleep each night.

Non-REM (non-rapid eye movement) sleep has 3 stages.

  • Stage 1. This stage lasts a few minutes as you drift from being awake to being asleep.
  • Stage 2. Your body’s systems relax further, your core temperature drops, and your brain waves are slower. You spend about 50 percent of your sleep cycle in this phase.
  • Stage 3. This phase is also known as “slow wave sleep.” It’s when your heart rate, breathing, and brainwaves are slowest.

REM (rapid eye movement) sleep is the part of your sleep cycle when you have vivid dreams.

A sleep cycle lasts about 90 minutes, and during that time you move through these four stages of sleep.

Most of your deeper slow wave sleep happens in the first half of the night, while REM sleep happens more during the second half of the night.

Researchers have found that when the HPA axis is overly active, it can disrupt your sleep cycles, causing:

  • fragmented sleep
  • insomnia
  • shortened overall sleep time

Those sleep disturbances can wreak further havoc on your HPA axis, distorting your body’s production of cortisol.

Studies have shown that insomnia and other forms of sleep deprivation cause your body to secrete more cortisol during the day, perhaps in an effort to stimulate alertness.

The HPA axis — and thus, your body’s cortisol levels — are affected by many of the same factors that influence other aspects of your overall health.

Outlined below are some of the ways that cortisol levels can be impacted, which may affect your ability to get a good night’s sleep.

Diet

Researchers have found that diets high in the following substances can profoundly affect the circadian production of cortisol:

  • animal proteins
  • refined sugars
  • salt
  • fat

Diets rich in fruits and vegetables are thought to promote the healthy cortisol production rhythms needed for sound, regular sleep.

Stress and trauma

Research shows that when you experience a stressful event — an exam or public speaking, for instance — the jolt of stress hormones is short-lived. Your body returns to normal cortisol levels fairly quickly.

But when stress is chronic or ongoing, the effects on your HPA axis and cortisol levels can last a long time.

Sometimes trauma causes cortisol levels to be too high for too long. This was seen in a study of the survivors of the Wenchuan earthquake in China in 2008. Researchers found elevated cortisol levels in the hair of all participants.

But the opposite can also be true. Researchers have found that trauma and PTSD can result in a chronic drop in cortisol levels.

Studies have shown lower cortisol levels in people who’ve survived a wide range of traumas. Usually, the earlier the trauma, the more permanent the change in HPA function and cortisol levels.

Holocaust survivors, for example, have repeatedly been found to have lower cortisol levels, decades after the war ended.

Similarly, research has also found that survivors of sexual assault, sexual abuse, and intimate partner violence often have lower levels of cortisol in their saliva, urine, or plasma.

The same has been found for Black people who regularly face racism in the United States.

Instead of the normal up-and-down cycles of cortisol release, trauma survivors’ cortisol levels may flatline, and their cortisol receptors may be especially sensitive in order to compensate.

Researchers think this may be an adaptation to an environment that constantly triggers the stress response.

Sleep disorders

Sleep disorders such as obstructive sleep apnea affect the HPA axis and cause spikes in cortisol production.

Researchers have found that patients whose continuous positive airway pressure (CPAP) machines were withdrawn during the night had elevated cortisol and blood glucose levels when they were tested.

Cushing’s syndrome or Cushing’s disease

Cushing’s syndrome is the chronic overproduction of cortisol.

The most common cause of Cushing’s syndrome is the long-term, high-dosage use of corticosteroid medications, such as prednisone.

Injectable steroids for the treatment of back or joint pain can also cause Cushing’s syndrome if used in high doses over a long period of time.

Cushing’s disease isn’t the same as Cushing’s syndrome.

With Cushing’s disease, elevated cortisol levels are caused by a tumor in the pituitary gland. This tumor causes the gland to create a high level of ACTH. This hormone then instructs your body to produce more cortisol than it needs.

Addison’s disease and adrenal insufficiency

Addison’s disease, also called primary adrenal insufficiency, is a rare disorder. It occurs when your adrenal glands produce too little cortisol. This disease can be caused by:

Secondary adrenal insufficiency is more common than Addison’s disease. If your pituitary gland is functioning as it should, it releases ACTH, which in turn signals your adrenal glands to make cortisol when your body needs it.

But with secondary adrenal insufficiency, there’s a problem with your pituitary gland. As a result, your adrenal glands don’t receive the signal to make cortisol when you need it. If your adrenal glands don’t get that message, they may eventually shrink.

Disrupted cortisol levels don’t only impact your ability to sleep. They can also affect other aspects of your health. For instance, disrupted cortisol levels can cause:

  • changes in your metabolism
  • weight gain
  • inflammation
  • memory problems
  • anxiety and depression
  • headaches
  • heart disease

If you’re having sleep issues, talk to your doctor about whether it’s safe to incorporate some of these strategies into your daily life to help lower your cortisol levels:

Balancing your cortisol levels can take time. While you’re working on it, here are some ways you can aim for a better night’s rest:

  • Keep your bedroom dark and cool. A temperature around 65°F (18.3°C) is ideal for sleeping.
  • Put away electronics before bedtime. The light from TVs, tablets, laptops, or phones can stimulate your brain and make it harder to fall asleep.
  • Eliminate noise. Use a fan or white noise machine to drown out noises that may disrupt your sleep.
  • Skip caffeinated drinks in the late afternoon or evening.
  • Swap the cocktail for chamomile tea, but finish drinking any beverage at least an hour before bedtime to avoid waking up to use the bathroom.

The stress hormone cortisol is produced by the HPA axis, which also helps coordinate your sleep cycles.

When the HPA axis is disrupted through poor nutrition, chronic stress, or illness, this can result in insomnia and other sleep disturbances.

If you’re experiencing sleep issues and think cortisol could be playing a role, talk with your doctor.

Your doctor may encourage you to make changes to your diet, exercise habits, or sleep hygiene.

Medication, relaxation techniques, and therapy may also help you bring down cortisol levels so you can get the regular rest you need.