- Melatonin is a naturally occurring hormone primarily produced by the pineal gland, a small endocrine organ located deep in the brain between the two hemispheres, near the center of the brain.
- Often referred to as the “sleep hormone,” melatonin plays a central role in regulating the body’s circadian rhythms, particularly the sleep–wake cycle. Its production is closely linked to the light–dark cycle: melatonin levels rise in response to darkness and fall during exposure to light, effectively helping to synchronize the body’s internal clock with the external environment.
- Melatonin synthesis begins with the amino acid tryptophan, which is converted into serotonin and subsequently transformed into melatonin in pinealocytes, the primary cells of the pineal gland. The regulation of melatonin production is controlled by the suprachiasmatic nucleus (SCN) of the hypothalamus, the brain’s master clock, which receives direct input from the retina. As night falls, the SCN sends signals that increase melatonin synthesis, peaking in the middle of the night and gradually decreasing toward morning. This rhythmic secretion of melatonin promotes drowsiness, lowers core body temperature, and supports sleep initiation and maintenance.
- Beyond sleep regulation, melatonin is involved in a variety of biological functions. It acts as a potent antioxidant, scavenging free radicals and reducing oxidative stress, which helps protect cells from damage. Melatonin also has anti-inflammatory properties and influences immune function, metabolism, and reproductive hormones. In some animals, melatonin is crucial for seasonal reproduction, responding to changes in day length. In humans, while its influence on reproduction is less dramatic, it may play a role in puberty onset and regulation of menstrual cycles.
- Melatonin levels naturally vary with age. In newborns, production is minimal but begins to increase after a few months, helping infants to develop a more regular sleep cycle. Levels peak in early childhood and then decline gradually throughout life. Older adults often have significantly lower melatonin levels, which may contribute to the sleep disturbances commonly experienced with aging.
- Clinically, melatonin has been widely used in the treatment of sleep disorders, including insomnia, jet lag, shift work disorder, and delayed sleep phase syndrome. As an over-the-counter supplement, synthetic melatonin is generally considered safe and effective for short-term use, especially for adjusting the circadian rhythm in cases of travel or shift changes. It has also been explored as a potential adjunct treatment in conditions such as seasonal affective disorder (SAD), migraine, cancer, and neurodegenerative diseases like Alzheimer’s and Parkinson’s disease, due to its neuroprotective and antioxidant effects.
- However, melatonin is not without limitations. Its effectiveness can vary depending on dosage, timing, individual physiology, and the specific sleep issue being treated. Taking melatonin at the wrong time of day can disrupt circadian rhythms rather than correct them. Additionally, because melatonin is classified as a dietary supplement in many countries (including the United States), it is not tightly regulated, and the actual content in over-the-counter products may differ from what’s labeled.
