In today’s fast-paced world, a good night’s sleep is a luxury many can’t afford. Online media has spread numerous misconceptions about sleep and perpetuated wellness trends that often skim over the main underlying causes of sleep disturbances. To guide our biological clocks, our sleep cycle interacts with several hormones, including melatonin, cortisol, estrogen/progesterone, testosterone, and thyroid hormones. When the synchronicity between our hormones and the sleep-wake cycle is disrupted, due to stress, medical conditions, or poor lifestyle habits, sleep problems like insomnia and fatigue may start to emerge. This article will delve into the main hormonal factors that influence our sleep and how such factors can be managed to help us take informed steps towards improving our sleep quality.
Many of our body’s key biological processes are regulated by the endocrine system, a complex network of glands that secrete hormones into our bloodstream. These chemical messengers regulate vital physiological processes, including metabolism, growth, and sleep. Sleep regulation requires various glands and biological structures to work in tandem with one another to secrete hormones. These hormones follow a rhythmic release dictated by our body's internal biological rhythms.1
A third of our lifetime is comprised of sleep, an action guided by the autonomous mechanism of our biological clock: the circadian rhythm. Circadian rhythms incorporate the numerous physical, mental and behavioural changes we experience over a 24-hour cycle, e.g. the sleep-wake cycle.
The key regulator of our circadian system is the suprachiasmatic nucleus (SCN), a bundle of nerve cells located in the anterior hypothalamus above the optic region. Nerve cells within the SCN possess the ability to propagate following a circadian pattern. This pattern follows an endogenous rhythm of around 24 hours, and can also be shifted in response to external cues called zeitgebers (e.g., light, temperature).2
Light is the main environmental cue modulating SCN activity. It is received by the SCN through a direct neural pathway from the retina. The SCN interprets light signals based on the time of day. During the daytime, the SCN suppresses the release of melatonin, whereas when daylight diminishes, activity in the SCN decreases, triggering the pineal gland to secrete melatonin.3
The SCN also communicates with other regions of the hypothalamus and the pituitary gland to regulate the timing of hormone release from other glands, such as the adrenal cortex (cortisol) and thyroid. Therefore, it is through the SCN that the body can synchronise our biological clocks with the external daylight cycle.
Sleep occurs over 2 states: rapid eye movement (REM) and non-REM sleep.
Non-REM sleep consists of three stages, each leading us progressively deeper into rest until we reach the deepest phase, known as non-REM stage 3. This stage is often referred to as the restorative phase, during which growth hormones are released and brain activity diminishes, making it difficult to awaken.
REM sleep begins approximately 90 minutes after we fall asleep, marking the stage when dreaming occurs. The time we spend in REM sleep increases as the night progresses, but after around a 110-minute cycle, we return to non-REM sleep and the cycle repeats itself.8
Often dubbed the sleep hormone, melatonin is produced by the pineal gland in response to our bodies' circadian rhythms. While the exact function of melatonin is unknown, scientists have found a correlation between high levels of melatonin and better sleep quality. This explains why there is an increased secretion of melatonin at night and low levels during the daytime.4
Melatonin binds to melatonin receptors to facilitate the onset of sleep by reducing alertness, lowering our core body temperature, and putting us into a relaxed state suitable for sleep. It is often prescribed to people suffering from sleep disorders such as insomnia and jet lag to reduce sleep onset latency and increase sleep efficiency and duration.5
Cortisol, the stress hormone, is released by the adrenal gland and follows a 24-hour release rhythm inverse to melatonin. Cortisol release is regulated by the SCN, with its highest concentrations peaking around 9 am (when many people wake up). Concentrations of cortisol begin to decrease throughout the day, reaching their lowest levels around midnight. After about 2-3 hours of sleep, cortisol levels start to rise again, continuing this cycle.6
Cortisol induces a ‘fight-or-flight’ response in our bodies that increases our heart rate and breathing. As a result, heightened cortisol levels in sleep positively correlate with increased nocturnal awakenings and insomnia.
Women generally experience more sleep disturbances compared to men, and this can be attributed to the hormonal fluctuations during a woman’s menstrual cycle.7 Progestrone and estrogen are steroid hormones that play a crucial role in regulating the female reproductive system.
Progesterone is released during the luteal phase and acts as a natural sedative with sleep-promoting effects. Women demonstrate more slow-wave sleep during the initial luteal period, a stage where progesterone levels rise sharply. When progesterone levels start to decline during the late luteal phase, sleep disturbances become more common.
Estrogen plays a key role in regulating body temperature during sleep, keeping our temperature low during the night. It also has an impact on maintaining the quality of sleep by decreasing the number of awakenings and spontaneous arousals.9
Testosterone, primarily known as the male reproductive hormone, works in sync with our circadian rhythm to regulate its secretion. Levels of testosterone throughout the day are similar to those of cortisol, higher upon awakening and decrease during the day.
The release of testosterone is also synced to our non-REM/REM cycle, with levels rising during deep, slow-wave sleep. Men with lower levels of testosterone tend to spend less time in deep sleep, impacting both sleep duration and quality.10
The most common disruption to our sleep cycle, stress causes elevated levels of cortisol and disrupts melatonin secretion, making it difficult to wind down.
In women, the onset of menopause greatly decreases levels of progesterone and oestrogen, causing night sweats, insomnia, and various other sleep disturbances. Additionally, symptoms of menopause, such as hot flashes and mood disorders, can further lower the quality of sleep.
As men age, their testosterone levels start lowering, resulting in reduced sleep efficiency, increased nocturnal awakenings, and less time in slow-wave sleep.
Lifestyle habits such as shift work disrupt our natural circadian rhythms by keeping us awake at hours we should be asleep. This results in an interference with the normal timing of melatonin secretion, leading to insomnia and reduced REM sleep.6
An imbalanced diet high in sugars, caffeine, and processed food also interferes with hormones that regulate satiety and energy.
Obese individuals tend to have excess fat around their necks and throats, causing them to suffer from obstructive sleep apnea.
Potential signs that there may be underlying hormonal balances impacting your sleep are:
If these symptoms persist, it is crucial to seek medical help to conduct salivary or blood tests:
While some sleep disturbances can be fixed by hormone therapy, it is crucial to be mindful of our lifestyle habits:
Hormones play a foundational role in regulating our sleep-wake cycle, therefore, it is crucial to understand this relationship so we can make informed choices about our sleep health.
Women tend to experience more hormonal imbalances due to changes during menstruation or when they enter menopause.
While several hormones play roles in sleep regulation, melatonin is the most important one as it signals to our body when it is time to be asleep.
The most effective approach would require medical evaluation and differs depending on everyone’s needs. Managing stress and changing our diets is the first and easiest step we can take to target our sleep disturbances. If symptoms persist or worsen, consult a medical professional for personalised treatments such as hormone therapy or supplements
