Melatonin: The Sleep Hormone, Its Longevity Biology, and How to Use It Correctly
Melatonin is the most popular sleep supplement in the world and one of the most consistently misused. Most people take too much (the pharmacological doses sold in the US are 5 to 10 times higher than the physiological doses that work), at the wrong time, and with the wrong expectations. Melatonin is a chronobiotic — a circadian rhythm synchronizer — not a sedative. Understanding this distinction is the key to using it effectively.
- Melatonin is a hormone produced by the pineal gland in response to darkness, with secretion beginning approximately 2 hours before habitual sleep time (the dim-light melatonin onset, or DLMO) and peaking in the middle of the biological night before declining in the early morning. It signals darkness and biological night to every cell in the body — it does not cause sleep, but it signals that sleep time has arrived.
- The physiological effective dose of melatonin for circadian entrainment is 0.1 to 0.5 mg — far below the 5 to 10 mg doses commonly sold in the US. Doses above 0.5 mg do not produce proportionally greater circadian effects but do produce sedation-like effects via non-circadian mechanisms, which is likely why high-dose melatonin produces the feeling of grogginess rather than sleep quality improvement.
- Melatonin is most effective as a chronobiotic — a tool for phase-shifting the circadian clock. Taking 0.5 mg 5-6 hours before the current DLMO advances the clock (useful for evening chronotypes who want to fall asleep earlier); taking it in the morning delays the clock (useful for jet lag recovery from westward travel). Timing is everything — melatonin taken at the wrong phase can worsen circadian alignment.
- Melatonin has substantial antioxidant activity beyond its circadian function — it is a potent scavenger of hydroxyl radicals and peroxyl radicals and stimulates multiple antioxidant enzyme systems. Mitochondrial melatonin is particularly important for protecting mitochondrial membranes from oxidative damage. Melatonin declines significantly with aging (elderly adults produce 75 percent less melatonin than young adults), which may contribute to both sleep disruption and increased oxidative stress in older populations.
- For jet lag specifically, melatonin 0.5 mg taken at the destination bedtime for 3-4 nights is one of the most effective evidence-based interventions available — significantly faster than light-based protocols alone. For general sleep improvement without circadian disruption, improving sleep hygiene (consistent wake time, morning light, evening darkness, cool bedroom) is more effective than melatonin supplementation.
Melatonin became available as an over-the-counter supplement in the United States in 1994 and has since become the most widely used sleep supplement globally. An estimated 3.1 percent of US adults use melatonin — a figure that has tripled in the past decade. The popularity is understandable: poor sleep is endemic, melatonin is natural, cheap, and available without prescription. The problem is that most people are using it incorrectly — taking doses 10 to 50 times higher than the evidence supports, at times that may worsen their circadian alignment rather than improve it.1
What Melatonin Actually Is
Melatonin (N-acetyl-5-methoxytryptamine) is produced by the pineal gland from serotonin in a two-step process requiring the enzymes AANAT and HIOMT. Its production is driven by the suprachiasmatic nucleus — which receives direct retinal light input — and begins in response to darkness, typically 2 hours before habitual sleep time (the dim-light melatonin onset, DLMO). Serum melatonin rises through the early biological night, peaks around 2 to 3 AM, and declines through the second half of the night as dawn approaches.2
Critically: melatonin does not cause sleep. It signals darkness and biological night to every tissue in the body — it is the darkness hormone, not the sleep hormone. Melatonin receptors (MT1 and MT2) are distributed throughout the body: the SCN (where melatonin reinforces circadian phase), the retina, the gut, the immune system, reproductive organs, and virtually every peripheral tissue. The sleep-promoting effect of melatonin in humans is primarily chronobiotic — it adjusts the timing of the circadian clock rather than directly inducing sedation.
The Dose Problem
Most melatonin supplements sold in the US contain 5 to 10 mg of melatonin per tablet — doses that produce plasma melatonin concentrations 10 to 100 times higher than physiological nighttime peaks. Studies by MIT researchers have established that the physiologically active dose for circadian phase shifting is 0.1 to 0.5 mg — doses that produce plasma concentrations approximating the physiological range. Higher doses do produce subjective sedation (likely via direct effects on sleep systems independent of circadian signaling) but do not produce better circadian entrainment and may produce grogginess, next-day fatigue, and paradoxical sleep disruption at very high doses.3
Why does the market offer 5 to 10 mg doses? Partly because more is culturally equated with stronger effects, partly because supplement manufacturers are not required to prove efficacy at their marketed doses, and partly because the sedating effects of high-dose melatonin create the subjective impression of improved sleep even when sleep architecture is not actually improved. The evidence-based recommendation: 0.3 to 0.5 mg taken 30 to 60 minutes before intended sleep time for general use.
The Longevity Biology of Melatonin
Beyond circadian signaling, melatonin has significant biological activities with direct longevity relevance. Melatonin is among the most potent known scavengers of hydroxyl radicals and interacts with MT1/MT2 receptors to activate antioxidant enzyme systems including superoxide dismutase and glutathione peroxidase. Unlike most antioxidants, melatonin and its metabolites (particularly AFMK and AMK) are themselves antioxidants, creating a cascade of antioxidant activity from a single melatonin molecule.4
Mitochondrial melatonin is particularly important: melatonin concentrates in mitochondria (where its synthesis may actually occur independently of the pineal gland) and protects mitochondrial membranes from lipid peroxidation by the ROS generated by the electron transport chain. Mitochondrial melatonin supplementation has demonstrated protective effects in multiple models of mitochondrial dysfunction. Melatonin declines dramatically with aging: elderly adults produce approximately 75 percent less melatonin than young adults, with the decline beginning in the 40s and accelerating after 70. This age-related decline correlates with declining sleep quality and may contribute to increased oxidative stress in aged tissues.
References
- 1Savage RA, et al. "Melatonin." StatPearls. National Library of Medicine. 2023. [PubMed]
- 2Arendt J. "Melatonin and the pineal gland: influence on mammalian seasonal and circadian physiology." Reviews of Reproduction. 1998;3(1):13-22. [PubMed]
- 3Lewy AJ, et al. "The circadian basis of winter depression." PNAS. 2006;103(19):7414-7419. [PubMed]
- 4Reiter RJ, et al. "Melatonin as an antioxidant: under promises but over delivers." Journal of Pineal Research. 2016;61(3):253-278. [PubMed]
- 5Brzezinski A, et al. "Effects of exogenous melatonin on sleep: a meta-analysis." Sleep Medicine Reviews. 2005;9(1):41-50. [PubMed]