Sleep is a vital biological process that allows our bodies and minds to recharge and recover from the previous day. While we may take sleep for granted, it is actually regulated by several biological factors and sleep-related hormones. In this article, we will explore the major hormones involved in regulating the sleep-wake cycle and understand their roles in helping us fall and stay asleep.
The sleep-wake cycle
Healthy sleep consists of cycles of non-REM (rapid eye movement) and REM sleep stages. Non-REM sleep makes up 75-80% of our sleep and progresses through three stages: stage 1 or light sleep, stage 2 or true sleep, and stage 3 or deep sleep. REM sleep accounts for the remaining 20-25% and is when most dreaming occurs. Together, these stages promote physical restoration and memory consolidation in the brain.
The sleep-wake cycle is regulated by two main biological processes: sleep homeostasis and the circadian rhythm. Sleep homeostasis tracks your need for sleep based on the amount of prior wakefulness. The longer you are awake, the more pressure builds for sleep. The circadian rhythm acts as the internal clock that regulates periods of sleepiness and wakefulness over a 24-hour period. It helps synchronize sleep to nighttime hours.
Key hormones involved in sleep regulation
There are several key hormones involved in controlling both sleep homeostasis and the circadian rhythm:
Melatonin
Melatonin is often called the “sleep hormone” because it plays a major role in regulating sleep. It is secreted by the pineal gland in the brain. Melatonin levels begin to rise in the evening as part of the circadian rhythm, promoting sleepiness and reaching peak levels at night.
Darkness stimulates melatonin production while light inhibits it. Melatonin induces sleep by lowering body temperature, inducing drowsiness, and setting the biological clock to nighttime mode. Melatonin levels naturally decrease in the early morning hours.
Cortisol
Cortisol is a steroid hormone released by the adrenal glands on a 24-hour circadian rhythm. Often called the “stress hormone,” cortisol helps control blood sugar, metabolism, and blood pressure. Cortisol levels are highest in the early morning right before waking to help energize you for the day.
Abnormally high cortisol at night can disrupt sleep by promoting alertness. Likewise, low nighttime cortisol can cause excessive daytime sleepiness. Maintaining a healthy circadian cortisol rhythm is important for consistent sleep-wake cycles.
Growth hormone
Human growth hormone (HGH) is essential for growth and cell regeneration. HGH is secreted in pulses, with the largest pulse occurring about an hour after falling asleep. Most daily production takes place at night during deep, non-REM sleep stages.
HGH helps stimulate protein production needed for muscle growth and repair. It also regulates metabolism and body fat. Getting quality deep sleep allows for optimal HGH release.
Prolactin
Prolactin is responsible for stimulating breast milk production in women after pregnancy. It is produced mainly by the pituitary gland, with levels rising throughout the night and peaking in the early morning hours around REM sleep.
Some research suggests prolactin may play a role in REM sleep regulation and have sedative effects to promote deeper sleep. However, its exact sleep-related functions are still being studied.
Other hormones affecting sleep
Some other hormones that may influence sleep include:
- Thyrotropin – Stimulates the thyroid gland; levels peak at night
- Insulin – Manages blood glucose; counteracts waking effects of cortisol
- Orexin – Promotes wakefulness and appetite
- Ghrelin – Stimulates hunger; levels rise before scheduled mealtimes
- Leptin – Suppresses appetite; levels rise during sleep
- Estrogen – Fluctuates with menstrual cycles; affects temperature regulation
Sleep disorders related to hormone imbalance
Imbalances with sleep-related hormones can contribute to certain sleep disorders:
Insomnia
Insomnia often involves low melatonin secretion at night and abnormal circadian rhythms that prevent restful sleep. Cortisol abnormalities causing nighttime alertness may also play a role.
Sleep apnea
Sleep apnea leads to impaired sleep from disrupted breathing. It is linked to abnormalities in GH, cortisol, and thyroid hormone levels that may compound symptoms.
Restless legs syndrome
RLS features uncomfortable leg sensations that create an urge to move them. It may be related to low nighttime prolactin secretion. Dopamine abnormalities may also contribute.
Delayed sleep-wake phase disorder
This disorder involves a misalignment between the circadian clock and external daylight cycles. Melatonin secretion may not adapt properly to nighttime hours.
Tips for optimizing sleep hormones
Here are some tips that can help optimize your sleep hormone profiles:
- Maintain a regular sleep-wake schedule to entrain circadian rhythms
- Make sure your bedroom is completely dark at night
- Avoid bright lights and screens before bedtime
- Take melatonin supplements a few hours before bed if needed
- Reduce stress through relaxation techniques to lower cortisol
- Avoid large meals, alcohol, and caffeine close to bedtime
- Get regular exercise during the day to promote deeper sleep
- Ask your doctor about hormone testing if a sleep disorder is suspected
Conclusion
Proper sleep is vital for optimal health and regulated by a number of hormones throughout the day and night. The sleep-wake cycle is controlled by the interaction between the hormones melatonin and cortisol using both the circadian rhythm and sleep homeostasis. Growth hormone, prolactin, and several other hormones also influence sleep stages and bodily processes at night.
Getting adequate sleep consistency allows these hormones to coordinate biological processes for restoration and waking performance. Sleep disorders may be related to underlying hormone abnormalities. Optimizing sleep hygiene habits and consulting a physician can help identify and address potential hormonal causes of sleep problems.