Amid a global sleep crisis—with 30% of adults sleeping <6 hours daily, 31% of school-age adolescents <8 hours nightly, and insomnia more common in adult women (per Bixler et al., 2001)—this article examines melatonin (MT) and its role in sleep disorders. It covers sleep disorder types (insomnia, hypersomnia, parasomnias) and influences (age, gender, socioeconomic status/occupation), then details melatonin: its 1958 discovery, pineal/extrapineal sources, circadian secretion (peaking 2–4 AM), functions (regulating sleep-wake cycles, antioxidant, neuroendocrine-immune support), and liver metabolism. Finally, it notes melatonin’s adjunctive role in improving sleep (aiding onset, reducing nighttime awakenings) when medically guided, framing it as a biology-based solution for sleep disturbances.
Night falls, yet countless lights remain on in homes, offices, and classrooms across the globe—each glowing space a silent sign of disrupted rest. For many, the transition from wakefulness to sleep has grown from a natural rhythm into a daily struggle: minds race with unfinished tasks long after dark, bodies ache with fatigue but refuse to settle, and mornings bring the fog of too little rest, making even routine activities feel overwhelming. These struggles are not isolated to a few; they are threads woven into the fabric of a global sleep crisis that cuts across age, career, and location. Once taken for granted as an effortless part of daily life, sleep has now become a precious, often elusive commodity for millions.
It is no exaggeration to call sleep the “unsung hero” of health: its quality, length, and consistency act as a direct barometer of our overall well-being. Persistent, repeated sleep disruptions do more than leave us feeling groggy—they slowly erode physical health, impair focus and cognitive function, and weaken our ability to cope with stress or emotional challenges. The scale of the problem is staggering, as statistics reveal: 30% of adults worldwide get fewer than 6 hours of sleep each day, and 31% of adolescents sleep less than 8 hours per night during school weeks—well below the recommended amounts for their age groups.
A landmark 2001 study by Bixler and colleagues further illuminates how sleep disorders evolve with age: their prevalence rises steadily until the age of 60, after which rates level off. Gender also shapes sleep health, though its impact shifts across the lifespan. In childhood, boys and girls face similar risks of sleep disorders, but differences emerge once adolescence begins. For adults, a comprehensive meta-analysis has confirmed that insomnia is more common in women than in men.
Socioeconomic status and occupation add another layer of complexity to sleep trends. While factors like income and education indirectly influence sleep quality—for example, by affecting access to comfortable living conditions or stress levels—unemployment has a direct link to higher insomnia risk, likely tied to financial anxiety and disrupted daily routines. Importantly, sleep disorders are not limited to insomnia (too little sleep) or excessive sleepiness (too much sleep); they can also manifest as unusual behaviors during rest, such as sleepwalking, sleep talking, or sudden nighttime movements.
Amid this widespread crisis, one naturally occurring substance has become a key focus of research: melatonin (MT). Produced by the pineal gland in the brain, this hormone plays a pivotal role in regulating the body’s sleep-wake cycle. For those grappling with sleep disturbances, it offers a potential lifeline—one rooted in the body’s own biological processes.
An Overview of Melatonin
Melatonin, chemically known as N-acetyl-5-methoxytryptamine, was first identified and isolated from the pineal glands of cows in 1958 by scientist Aaron Lerner. As the primary hormone secreted by the pineal gland, its core function is to regulate circadian rhythms and the sleep-wake cycle. Its secretion follows a distinct daily pattern: levels rise at night to help the body transition into sleep, while daylight triggers a reduction in secretion, keeping the brain alert and awake.
Chemical structure of melatonin
Melatonin production begins in humans around 3 to 4 months after birth, peaks just before puberty, and then gradually declines throughout adolescence and adulthood. By old age, melatonin levels reach their lowest point—a biological shift that is widely believed to be a major contributor to the sleep problems commonly experienced by older adults. While the pineal gland is the most well-known source of melatonin, the hormone is also produced in other parts of the body, known as “extrapineal sources.” These include the retina, bone marrow cells, platelets, skin, lymphocytes, Harderian glands, cerebellum, and, notably, the gastrointestinal tissues of vertebrates.
The Circadian Rhythm of Melatonin Plasma Concentration
Synthesis and Secretion
The synthesis of melatonin is tightly controlled by the nervous system, following a specific pathway. It starts in the paraventricular nucleus of the hypothalamus, which sends signals—either directly or indirectly—to the preganglionic sympathetic neurons located in the first thoracic segment of the spinal cord. From there, these signals are transmitted to the postganglionic sympathetic neurons of the superior cervical ganglion. These neurons then extend nerve fibers (known as pineal nerves) to the pineal gland, where they regulate the synthesis of melatonin.
Visible light entering the eye and the cascading positive and negative signalling pathways to neuronal structures in the mamallian brain that may follow: When the eyes are exposed to sunlight, the pineal gland's melatonin production is suppressed, resulting in the secretion of hormones that promote wakefulness. Conversely, in the absence of light, the pineal gland synthesizes melatonin unabated, leading to feelings of drowsiness and facilitating the onset of sleep.
Melatonin secretion exhibits a strong circadian rhythm, with light being the primary external regulator. Light information is detected by the retina and transmitted to the suprachiasmatic nucleus (SCN) of the hypothalamus—the brain’s “internal clock.” The SCN then relays this information to the pineal gland to adjust melatonin production. In humans, melatonin secretion typically begins shortly after sunset, reaches its highest concentration between 2 AM and 4 AM (during the middle of the night), and gradually decreases as dawn approaches. Approximately 80% of the body’s daily melatonin production occurs at night, resulting in a serum concentration ranging from 80 to 120 picograms per milliliter (pg/ml) during this period. In contrast, daytime serum melatonin levels are significantly lower, usually between 10 and 20 pg/ml.
The Functions of Melatonin
Melatonin serves a variety of critical functions within the body, extending beyond its role in sleep regulation.
First, it exerts an inhibitory effect on the hypothalamic-pituitary-gonadal (HPG) axis—a key system that controls reproductive function. Specifically, melatonin reduces the levels of gonadotropin-releasing hormone (GnRH), gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). It also acts directly on the gonads (ovaries in females, testes in males) to lower the production of sex hormones, including androgens, estrogens, and progesterone.
Circadian rhythm of melatonin plasma concentration
Second, melatonin possesses powerful neuroendocrine-immunomodulatory activity and robust antioxidant properties that help neutralize harmful free radicals. These characteristics are essential for maintaining the body’s overall health, as they support immune function, protect against oxidative stress, and may even play a role in preventing age-related damage to cells and tissues.
Third, melatonin is primarily metabolized in the liver. As a result, damage to liver cells (e.g., from liver disease, alcohol abuse, or certain medications) can disrupt the body’s ability to process melatonin, leading to abnormal levels of the hormone in the bloodstream.
The Definition and Classification of Sleep Disorders
Sleep disorders refer to a group of conditions characterized by abnormal sleep quantity (either too much or too little) or abnormal behaviors during sleep. They represent a disruption of the natural, rhythmic alternation between sleep and wakefulness. These disorders can arise from a wide range of factors, and they are frequently associated with underlying physical or mental health conditions. Sleep disorders are broadly categorized into two main types: sleep-wake disorders (also called sleep dysregulations) and parasomnias.
Excessive Sleepiness (Hypersomnia)
This category includes conditions where individuals experience an abnormal increase in sleep quantity or an overwhelming, uncontrollable urge to sleep during the day. Examples include excessive sleepiness or stupor caused by brain disorders, endocrine imbalances, or metabolic abnormalities. One well-known condition in this group is narcolepsy, a neurological disorder triggered by brain dysfunction. Narcolepsy is characterized by sudden, brief episodes of uncontrollable sleep (usually lasting less than 15 minutes) that can occur at inappropriate times (e.g., during work, school, or even while driving). These episodes are often accompanied by other symptoms, such as cataplexy (sudden loss of muscle tone), sleep paralysis (temporary inability to move upon waking or falling asleep), and hypnagogic hallucinations (vivid sensory experiences while transitioning into sleep).
Insufficient Sleep (Insomnia)
Insomnia is defined as getting fewer than 5 hours of sleep per night, and it manifests in several ways: difficulty falling asleep (onset insomnia), frequent awakenings during the night (maintenance insomnia), or waking up too early in the morning and being unable to fall back asleep (terminal insomnia). Insomnia can be triggered by a variety of factors, including:
- Environmental factors: Excessive light in the bedroom, loud noise from neighbors or traffic, or an uncomfortable mattress/pillow.
- Physical factors: Chronic pain (e.g., from arthritis or back issues), itching (e.g., from eczema), or severe coughing (e.g., from asthma or a respiratory infection).
- Psychological factors: Feelings of anxiety, fear, grief, or excitement (e.g., from a major life event like a wedding or job interview).
Insomnia is also a common symptom of many mental health conditions, such as neurasthenia, generalized anxiety disorder, and major depressive disorder.
Parasomnias
Parasomnias are a group of sleep disorders involving abnormal behaviors, emotions, or perceptions that occur during sleep or during the transitions between sleep and wakefulness. Examples include sleepwalking, sleep talking (somniloquy), night terrors (intense fear and screaming during sleep), nightmares (disturbing dreams that cause awakening), teeth grinding (bruxism), involuntary laughter, and involuntary muscle or limb twitches. Importantly, these episodes do not occur throughout the entire night; instead, they tend to happen during specific stages of sleep (e.g., slow-wave sleep for sleepwalking, rapid eye movement (REM) sleep for nightmares).
The Relationship Between Melatonin and Sleep Disorders
Melatonin is a cornerstone of the body’s sleep-wake regulatory system. Under natural conditions, the brain produces almost no melatonin during the day—thanks to the inhibiting effect of sunlight. As evening approaches and light levels decrease, the pineal gland begins to ramp up melatonin production. Around 9 PM, melatonin secretion accelerates sharply, sending a clear “sleep signal” to the brain and helping the body ease into a state of rest. By modulating this natural sleep process, melatonin can help overcome sleep disorders and enhance overall sleep quality.
The Adjunctive Therapeutic Role of Melatonin in Sleep Disorders
Melatonin is generally effective for treating insomnia, but it is critical that it be used under the guidance of a healthcare provider to ensure safety and appropriate dosing. Its key benefits for sleep disorders include:
- Regulating the sleep-wake cycle: By aligning the body’s internal clock with the external day-night cycle, melatonin helps correct circadian rhythm disruptions (e.g., jet lag, shift work disorder).
- Alleviating anxiety: Melatonin has mild anxiolytic (anxiety-reducing) properties, which can help calm a racing mind and make it easier to fall asleep.
- Reducing nighttime awakenings: By promoting deeper, more restful sleep, melatonin can decrease the number of times individuals wake up during the night.
For optimal results, melatonin should be taken before bedtime. This timing aligns with the body’s natural rhythm: as light fades in the evening, the pineal gland naturally increases melatonin synthesis and release, and supplemental melatonin can reinforce this biological process to facilitate sleep onset.
References
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Fougerou, C., Jaafari, N., Bellissant, E., et al. (2017). Melatonin: Pharmacology, Functions and Therapeutic Benefits. Current Neuropharmacology, 15(3), -. https://doi.org/10.2174/1570159X14666161228122115
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Repova, K., Baka, T., Krajcirovicova, K., Stanko, P., Aziriova, S., Reiter, R. J., & Simko, F. (2022). Melatonin as a Potential Approach to Anxiety Treatment. International Journal of Molecular Sciences, 23(24), 16187. https://doi.org/10.3390/ijms232416187