In this edition, we're diving into a specific facet of the sleep-wake cycle: the relationship between cortisol and sleep.

Cortisol, a hormone produced by the adrenal glands that sit atop the kidneys, plays several roles in the human body, including regulating blood sugar, blood pressure, and body temperature. The hormone is best known for its role in the stress response — aka “fight-or-flight” mode — a physiological reaction to a perceived threat that triggers a cascade of changes in the body to help us survive. 

However, one of its lesser-known roles is helping to control the sleep-wake cycle in our bodies. It turns out this hormone helps regulate sleep in several ways, both directly and indirectly. 

During the day, cortisol helps keep us awake by suppressing the production of melatonin, a hormone that encourages sleep. At night, it helps keep us asleep by suppressing wake-promoting neurotransmitters, like dopamine and norepinephrine, and by stimulating the release of GABA, a neurotransmitter that makes us feel calm and relaxed. When night falls, our bodies produce less cortisol, which allows melatonin to take its place as the dominant hormone in the brain and facilitates sleep.

As we know, sleep is essential for health. It's the time when our bodies and brains recover and repair themselves after a long day of activity. Whether it’s lack of sleep or a high-pressure deadline at work, our bodies often call upon cortisol to help us deal with stressful situations. Chronic sleep deprivation can cause elevated cortisol levels, have detrimental effects on our body's ability to maintain homeostasis, and even disrupt the immune system. 

At the same time, sleep can play a critical role in helping us manage our cortisol levels. Cultivating healthy sleep hygiene can lower cortisol, reduce the risk of physical and psychological illness, and improve sleep quality.

Read on to learn more about the relationship between cortisol and sleep and what you can do to keep them in harmony.

What Is Cortisol, and Why Should I Care?

If you've ever felt stressed, you've probably experienced the symptoms of cortisol. Also known as the “stress hormone,” cortisol is a steroid hormone produced in the adrenal glands in response to stress, exercise, and low blood sugar. The primary function of cortisol is to mobilize the body's resources, such as glucose and fat, to deal with a stressor.

When you think of stress, you probably first think of the physical manifestations: an increased heart rate, tight chest, clenched jaw, sweaty palms. The action of stress hormones, such as cortisol, is responsible for these physical symptoms — a series of chemical reactions that prepare the body for a “fight-or-flight” response.

Cortisol is released by the adrenal glands in response to a stressful event or situation, but it's also released in response to the anticipation of a stressful event or situation. Both acute and chronic stress are known to increase the level of cortisol in the bloodstream, which, in turn, affects several areas of the brain and body.

How Do Sleep Cycles Work Again?

Sleep cycles are regulated by the hypothalamus, which maintains the circadian rhythm, often referred to as the body’s “biological clock.” This is the same part of the brain that modulates our body temperature, hunger, thirst, and the release of certain hormones. 

The hypothalamus controls body and sleep patterns by sending out signals and transmitting them to many parts of the body. The pineal gland is another critical part of the brain that helps regulate the sleep cycle by releasing melatonin, a key hormone that dictates the body’s sleep-wake cycle.

When you’re asleep, you progress through different sleep stages, each associated with a specific physiological state and set of behaviors, such as brainwave patterns and muscle activity. As you advance through the stages of sleep, your brainwave patterns become slower, and you cycle through a repeating process of two distinct sleep states:  NREM (non-rapid eye movement) and REM (rapid eye movement). The sleep cycle is a repeating pattern of non-REM and REM sleep, which usually occur about four or five times during a typical night's sleep. (Source)

When you first fall asleep, you typically spend about 90 minutes in an NREM phase before entering a short period of REM sleep and begin dreaming. During REM sleep, your breathing and pulse increase and your body becomes paralyzed (which is an evolutionary safety mechanism in place to prevent you from acting out your dreams!). 

Non-REM sleep is divided into three stages:

• Stage one is a light sleep, characterized by theta waves in the brain, which occurs as you drift from being awake to falling asleep. 
• Stage two is a phase of deep sleep where you spend about 50% of your sleep cycle. While you may not be consciously aware of your physical state, your body transitions into this state by dropping your body temperature, relaxing your muscles, and slowing your brain waves. (Source)
• Stage three is the deepest sleep (aka slow-wave sleep), characterized by delta waves. Stage three is also the stage in which night terrors, sleepwalking, and bedwetting most often occur.

What Does Cortisol Have to Do With Sleep?

Sleep and cortisol are part of the “HPA axis”

The hypothalamus, the pituitary gland, and the adrenal glands work together in what is known as the hypothalamic-pituitary-adrenal (HPA) axis. Feedback from the hypothalamus and the pituitary gland influences the production of cortisol by the adrenal gland. Psychological and physical stressors activate the HPA and stimulate increased production of cortisol, which interferes with normal sleep. Because sleep inhibits the HPA and cortisol secretion, sleep deprivation becomes a further stressor promoting cortisol production. (Source, Source)

Sleep and cortisol possess a bidirectional relationship

Research has revealed that a two-way (bidirectional) relationship exists between sleep and cortisol, resulting in a vicious cycle when the body is thrown out of homeostasis. Lack of sufficient sleep, low-quality sleep, and inconsistent sleep schedules (as seen in night-shift workers) can all contribute to elevated cortisol levels. Elevated cortisol levels then contribute to an overactive HPA axis interfering with our ability to get enough high-quality sleep. Studies have shown that elevated levels of cortisol during sleep increase brain activity, reduce the amount of slow-wave sleep, and increase wakefulness throughout the night. (Source, Source, Source)

Sleep and cortisol both follow a circadian rhythm

Like sleep, research has shown that cortisol levels follow a diurnal rhythm (i.e., they rise and fall with the sun) and are typically highest in the early morning and lowest in the evening. According to studies, the lowest cortisol level typically occurs around midnight, begins to rise two to three hours after onset of sleep, and peaks about 45 to 60 minutes after you wake up in a phenomenon known as the “awakening response.” In this way, cortisol plays an important role in sleep-wake cycles: after encouraging wakefulness in the morning and alertness during the day, it declines in the evening so melatonin levels can rise and promote sleep. (Source)

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Sleep deprivation raises cortisol levels

When we don’t get enough sleep, our bodies tend to produce higher levels of cortisol. Sleep loss is considered a physiological stressor that can over-activate the HPA axis, causing the hypothalamus and pituitary gland to signal the adrenal system to constantly produce more cortisol. Some studies have shown elevated cortisol levels the evening after a single night of sleep deprivation, although these results have not been consistent. (Source)

Sleep and cortisol affect our metabolism

Studies show that sleep deprivation can increase circulating cortisol levels, thereby increasing blood sugar levels and decreasing insulin sensitivity. Researchers have also found a correlation between short sleep duration and an increased risk of developing obesity and type II diabetes. One long-term study followed nearly 500 participants from age 27 to age 40, finding that those who reported short sleep duration also tended to experience more weight gain and obesity. These findings were supported by a second study that looked at nearly 1,000 participants. This research suggests HPA axis hyperactivation may be one of the biological mechanisms responsible for the metabolic consequences of sleep loss. (Source, Source)

There’s a link between sleep disorders and elevated cortisol

While scientists have yet to uncover if sleep disorders cause elevated cortisol or vice versa, sleep conditions, including insomnia and obstructive sleep apnea, appear to be associated with HPA axis dysfunction (and therefore elevated cortisol levels at night). In one study, researchers removed continuous positive airway pressure (CPAP) machines from patients with obstructive sleep apnea during the night and found that they had elevated cortisol and blood glucose levels upon testing. (Source, Source)

What Can Cause Elevated Cortisol Levels?

Stress

‍An increased amount of stress in a person’s life can cause cortisol levels to rise. Stress can be caused by many things, such as family or relationship issues, financial problems, health concerns, or work.

Other hormonal imbalances

‍Hormonal imbalances can also cause cortisol levels to rise. Some examples of hormonal imbalances that may cause an increase in cortisol levels are polycystic ovary syndrome (PCOS) or adrenal hyperplasia.

Illnesses

‍Certain illnesses may cause cortisol levels to rise. Cushing’s syndrome is the most common illness that leads to an increase in cortisol levels. This condition can be caused by chronic use of glucocorticoid medications for conditions like asthma or, less commonly, tumors in the pituitary gland or adrenal glands. (Source)

What Are the Effects of High Cortisol Levels?

Cortisol helps maintain muscle mass and release stored sugar for energy,  but too much of it can increase belly fat, blood sugar levels, and inflammation. While cortisol is essential for survival, if you’re chronically stressed, you can become desensitized to cortisol’s effects, leaving you vulnerable to other stressors. This can lead to various health problems, including weight gain, immune system suppression, and increased inflammation. Although a direct connection between elevated cortisol levels and diseases such as cancer has yet to be made — it is well-accepted chronic inflammation contributes to diseases including cancer, cardiovascular disease, and Alzheimer's. (Source,  Source)

What Are the Signs and Symptoms of Elevated Cortisol?

The most common signs and symptoms of elevated cortisol levels include:

• Weight gain
• Difficulty losing weight
• Abdominal fat
• Water retention
• Oily skin or acne
• Thinning or loss of scalp hair
• Insomnia
• Muscle weakness
• Headache
• Increased appetite or cravings for sugar and carbs
• Depression
  

If you suspect you might have elevated cortisol levels, you can consult your doctor about testing options (via blood urine or saliva). Timed tests will provide you with a fuller picture of how your cortisol ranges over time.

What Should I Do About Sleep and Cortisol?

There are a number of steps you can take to lower cortisol overall, including making changes to your diet, adding dietary supplements, and making healthy lifestyle changes. Here are some tips to help you improve your sleep quality and tame your cortisol levels at the same time.

Cultivate good sleep hygiene

If you're having trouble falling asleep or staying asleep, some foundational steps you can take to get back on track include: setting a consistent sleep schedule, following a regular bedtime routine, and avoiding heavy meals at night. Light exposure at night can throw off your circadian rhythms, so keep electronics out of the bedroom, and turn off your TV and computer at least one hour before bed. Consider using a fan or a white noise machine to mask noises that may disturb your sleep. (Source)

Turn your bedroom into a cave

Keeping your bedroom dark and cool can help transition your body into sleep mode in the evening. Experts suggest aiming for a room temperature between 60 F and 70 F for ideal sleep conditions. This is because our body’s core temperature decreases at night to help us fall asleep. Another tip is to install blackout curtains on your windows to prevent sunlight or street lights from entering your room. (Source)

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Adopt a morning routine

Our bodies are designed to wake up with the sun. Unfortunately, many of us have jobs that require us to wake up way before the sun rises, which throws off our circadian rhythm and makes it harder to fall asleep at night. To get around this, try to wake up at roughly the same time every day, even on the weekends. When you wake up, don't turn on the lights or your computer — open your blinds, eat breakfast with natural light, and take a few minutes to stretch, breathe, and focus on your day ahead. 

Invest in a good mattress

Not only will a good night's sleep reduce your stress levels and boost your mood, it will also encourage nighttime secretion of human growth hormone, which is key for muscle repair and fat burning. Investing in a good mattress is key — your body is in contact with it for at least a third of your life, so it's worth the money to get one that's comfortable and spine-supporting. Studies have shown most people report getting their best sleep on medium-firm mattresses that are replaced regularly (the general rule is every seven or eight years, although this varies according to the mattress). (Source, Source)

Don't skip the magnesium

Magnesium is critical for relaxation and sleep and also plays a role in regulating cortisol levels. A study of 46 elderly patients found that daily supplementation of 500 mg of magnesium for eight weeks decreased cortisol levels and significantly increased sleep time. If you're having trouble sleeping, consult with your health care provider to determine if you might be magnesium deficient (according to research, roughly 50% of Americans may be consuming a magnesium-deficient diet!) and whether it might make sense to incorporate this essential mineral into your diet. (Source, Source)

Take a nap if you need one

If you need a pick-me-up in the afternoon, try taking a nap. Daytime napping after a night of sleep loss has been shown to cause beneficial changes in cortisol levels. One study from the American Journal of Physiology found that taking a two-hour nap after a sleepless night may lower cortisol levels and increase alertness and performance. (Source) 

Promote GABA activity

GABA (gamma-aminobutyric acid) is an amino acid derived from glutamic acid, one of the most common amino acids found in the body. GABA is an inhibitory neurotransmitter, meaning it helps calm brain activity and is used to treat anxiety, insomnia, and depression. It’s also regulated by the HPA axis and can help to support healthy HPA axis activity, while promoting feelings of relaxation. Although research on the effects of GABA supplementation on sleep is limited, the existing literature is promising — one study showed that subjects who took GABA fell asleep more quickly and experienced better sleep quality. For GABA-rich foods, incorporate cruciferous vegetables, beans, sweet potatoes, and rice onto your plate. (Source, Source, Source)

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