Melatonin: The Sleep Hormone, Its Longevity Biology, and How to Use It Correctly
Melatonin is a hormone that signals night to the body, and taken as a supplement it can shift the timing of the body clock.2 Its effect on sleep itself is modest,5 low doses can work as well as high ones,6 and supplement labels are often inaccurate.1 Here is what the evidence shows.
- Melatonin is secreted by the pineal gland with a strong daily rhythm, peaking during darkness; the length of secretion tracks the length of the night.2
- In people over 50 with insomnia, 0.3 mg taken 30 minutes before bed restored sleep efficiency and normal night-time melatonin levels; 3 mg also helped but kept melatonin elevated into the daytime and lowered body temperature.6
- Timing matters: low-dose melatonin taken in the morning shifts the body clock later, and taken in the afternoon or evening shifts it earlier, without causing sleepiness.3
- In laboratory research, melatonin reduces oxidative stress and concentrates in mitochondria; these are laboratory findings, not evidence that it slows human ageing.4
- Across 17 studies, melatonin shortened the time to fall asleep by about 4 minutes and added about 13 minutes of sleep; for jet lag and shift work, successful outcomes have been reported.5,2
In the United States, melatonin is sold as a dietary supplement, and what is in the bottle may not match the label. When researchers tested 31 supplements, melatonin content ranged from 83% below to 478% above the labelled amount, varied by as much as 465% between lots of the same product, and missed the label claim by more than 10% in over 71% of products; eight also contained serotonin.1
What Melatonin Actually Is
Melatonin is produced by the pineal gland with a marked daily rhythm: production peaks during darkness, and the length of secretion reflects the length of the night. Melatonin receptors are found in the brain, the retina, the pituitary gland and elsewhere.2
Taken as a supplement, melatonin can shift and in some cases reset circadian rhythms, lower body temperature and cause transient sleepiness, which is why it has been used for circadian rhythm problems such as jet lag and shift work.2
The Dose Problem
Dose matters more than many labels suggest. In a randomized trial in adults over 50, a 0.3 mg dose taken 30 minutes before bed restored sleep efficiency in those with insomnia and brought night-time melatonin to normal levels. A 3 mg dose also improved sleep but lowered body temperature and kept blood melatonin elevated into daylight hours, and people who slept normally were unaffected by any dose.6 Timing matters too: in winter depression research, low doses in the morning shifted the body clock later and doses in the afternoon or evening shifted it earlier, without causing sleepiness.3
For sleep itself, the effect is modest. A 2005 meta-analysis of 17 studies with 284 people found that melatonin shortened the time to fall asleep by 4.0 minutes, raised sleep efficiency by 2.2% and increased total sleep by 12.8 minutes.5 Jet lag affects most travellers crossing five or more time zones and is worse after eastward flights,7 and successful outcomes with melatonin have been reported.2
Melatonin and Ageing: What Is Known
In laboratory studies, melatonin reduces oxidative stress in several ways: it detoxifies reactive oxygen and nitrogen species directly, stimulates antioxidant enzymes, suppresses pro-oxidant enzymes and binds the metals that drive formation of the hydroxyl radical.4
Melatonin reaches high concentrations in mitochondria, and a 2016 review argued that it should be classed as a mitochondria-targeted antioxidant.4 These are laboratory findings: they do not show that taking melatonin slows ageing in people.
Put this research into practice: Supplement Evidence Database · Supplement Interaction Checker
References
- 1Erland LA, Saxena PK. "Melatonin Natural Health Products and Supplements: Presence of Serotonin and Significant Variability of Melatonin Content." J Clin Sleep Med. 2017;13(2):275-281. PubMed · DOI
- 2Arendt J. "Melatonin and the pineal gland: influence on mammalian seasonal and circadian physiology." Rev Reprod. 1998;3(1):13-22. PubMed · DOI
- 3Lewy AJ, et al. "The circadian basis of winter depression." Proc Natl Acad Sci U S A. 2006;103(19):7414-9. PubMed · DOI
- 4Reiter RJ, et al. "Melatonin as an antioxidant: under promises but over delivers." J Pineal Res. 2016;61(3):253-78. PubMed · DOI
- 5Brzezinski A, et al. "Effects of exogenous melatonin on sleep: a meta-analysis." Sleep Med Rev. 2005;9(1):41-50. PubMed · DOI
- 6Zhdanova IV, et al. "Melatonin treatment for age-related insomnia." J Clin Endocrinol Metab. 2001;86(10):4727-30. PubMed · DOI
- 7Herxheimer A. "Jet lag." BMJ Clin Evid. 2014;2014. PubMed
