Melatonin

Melatonin is the hormone produced by the pineal gland in response to darkness. It signals nighttime to the body's circadian clocks, initiates sleep onset, and has antioxidant properties. Its production declines with age and is suppressed by artificial light at night.

Melatonin synthesis begins with serotonin, which is converted to melatonin in the pineal gland under conditions of darkness. The process is initiated by signals from the suprachiasmatic nucleus (SCN), the master circadian clock in the hypothalamus. Light — specifically short-wavelength blue light — suppresses melatonin production via the ipRGC retinal pathway. This is why screen exposure in the evening delays melatonin onset and disrupts sleep architecture.

Melatonin peaks in the middle of the night (typically between 2–4am) and declines before waking. Its primary circadian role is signaling darkness to peripheral clocks throughout the body, coordinating the timing of hormonal rhythms, immune activity, and metabolic functions. Beyond sleep, melatonin is a potent antioxidant and free radical scavenger — one of the few antioxidants that crosses the blood-brain barrier with ease.

Melatonin production declines approximately 10% per decade after age 40. This contributes to the circadian rhythm fragmentation seen in older adults and may be a factor in the increased oxidative stress of aging. For women, the menstrual cycle modulates melatonin timing: onset occurs slightly earlier in the follicular phase and later in the luteal phase.

As a supplement, low-dose melatonin (0.3–0.5 mg) is typically used for circadian phase support (jet lag, delayed sleep phase). Higher doses (3–10 mg) are commonly sold but produce pharmacological rather than physiological effects and are not necessary for most use cases.

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