Melatonin is a naturally occurring hormone found in most animals and some other species such as algae. In humans and other vertebrate animals, this hormone is produced by the pineal gland, and it plays an important role in regulating sleep-wake cycles as well as in blood pressure regulation and seasonal reproduction. Several studies have also shown that melatonin also acts an antioxidant in both animals and plants.
Brief Explainer: How Melatonin Regulated Sleep-Wake Cycles and Promotes Sleep Onset in Humans and Animals
The pineal gland secretes melatonin and releases it in the bloodstream during the period of nocturnal darkness. It is a neuroendocrine transducer that sets the internal clock of animals, particularly by indicating the arrival and the length of the night.
Remember that the pineal gland starts producing melatonin at the onset of darkness. Both darkness and melatonin production signal the body to prepare for sleep. On the other hand, light decreases melatonin production and signals the body to prepare for wakefulness.
Different animals use different variations in the production of melatonin. Note that the onset of melatonin at dusk promotes sleep in diurnal animals and activity in nocturnal animals. In humans, infants produce high levels of melatonin between midnight and eight in the morning. Human melatonin production decreases as person ages. It is also worth noting that as children transitions to adolescence and further to adulthood, the nightly schedule of melatonin release becomes delayed.
Nevertheless, the discovery of melatonin and its role in regulating sleep-wake cycles in 1953 has prompted clinical researchers and pharmaceutical companies to introduce it as a supplement or medicine for treating sleep disorders such as insomnia and those who are having trouble sleeping due to jet lag and shift work schedule.
Studies: The Effectiveness of Melatonin Supplementation as a Sleep Aid and in the Treatment of Insomnia
Results of several studies have been mixed, and the effectiveness of melatonin in treating sleep disorders remains unclear. A meta-analysis of 12 studies by Fiona Auld et al. revealed that exogenous melatonin or taking melatonin supplements has an effect on reducing sleep onset latency in primary sleep insomnia, delayed sleep phase syndrome, and in regulating the sleep-wake patterns in patients.
Another study by E. Matheson and B. L. Hainer noted that controlled-release melatonin supplements have been recommended as a first-line agent for the short-term treatment of insomnia in people who are 55 years old and above. The supplement also a cheaper alternative to the drug ramelteon used for treating short-term insomnia and delayed sleep onset.
Numerous studies have also explored the effectiveness of melatonin supplementation in managing lifestyle-related sleep disorders. For example, a Cochrane systematic review by A. Herxheimer and K. J. Petrie revealed that daily doses of melatonin between 0.5mg to 5mg decreased jet lag from flights crossing five or more time zones, especially if taken closer to the target bedtime at the destination.
The same study by Herxheimer and Petrie noted that 5mg of melatonin helps people fall asleep faster and sleep better than the 0.5mg variant. However, doses above 5mg appear to be no more effective. The researchers also reminded that the timing of taking melatonin and its dose are important. Taking the supplement early in the day can cause immediate sleepiness and delayed adaptation to the local time.
Despite the studies mentioned above, there is no scientific consensus as regards the effectiveness of melatonin in managing and treating sleep disorders. A review by M. Brasure et al. of the Agency for Healthcare Research and Quality of the United States concluded that the evidence of the benefits of melatonin for the general population remains unclear. Another Cochrane review by Juha Liira et al. concluded that melatonin has limited effects against the sleep problems of people who are work night shifts and rotating shift schedules.
FURTHER READINGS AND REFERENCES
- Auld, F., Maschauer, E. L., Morrison, I., Skene, D. J., and Riha, R. L. 2017. “Evidence for the Efficacy of Melatonin in the Treatment of Primary Adult Sleep Disorders.” Sleep Medicine Reviews. 34: 10-22. DOI: 10.1016/j.smrv.2016.06.005
- Brasure, M., R. McDonald, Fuchs, E., Olson, C. M., Carlyle, M., Diem, S., Koffel, E., Khawaja, I. S., Ouellette, J., Butler, M., Kane, R. L., and Wilt, T. J. 2015. “Management of Insomnia Disorder.” AHRQ Comparative Effectiveness Review. 15(16). PMID: 26844312
- Liira, J., Verbeek, J. H., Costa, G., Driscoll, T. R., Sallinen, M., Isotalo, L. K., Ruotsalainen, J. H. 2014. “Pharmacological Interventions for Sleepiness and Sleep Disturbances Caused by Shift Work.” Cochrane Systematic Review. DOI: 10.1002/14651858.CD009776.pub2
- Matheson, E. and B. L., Hainer. 2017. “Insomnia: Pharmacological Therapy.” American Family Physician. 96(1): 29-35. PMID: 28671376
- Herxheimer, A. and Petrie, K. J. 2002. “Melatonin for the Prevention and Treatment of Jet Lag.” Cochrane Systematic Review. DOI: 10.1002/14651858.CD001520