Melatonin is produced by the pineal gland in response to darkness and signals the body that it is nighttime. It does not cause sleep directly, but it lowers core body temperature and suppresses the alerting signal from the circadian system, creating the physiological conditions for sleep initiation. Peak nocturnal melatonin is reached around 2 to 3am in young adults. With age, the amplitude of the nocturnal melatonin peak declines substantially, and the timing often shifts earlier, contributing to earlier bedtimes and earlier natural wake times. By 70, nocturnal melatonin may be as little as 10 percent of the level seen in young adults.
The Consequences of Reduced Melatonin
Reduced melatonin directly reduces sleep efficiency and slow-wave sleep depth. It also reduces the antioxidant activity that melatonin provides at high nocturnal concentrations, a property separate from its sleep-promoting effects. Melatonin is one of the most potent endogenous antioxidants in the body; its nocturnal surge provides significant mitochondrial and nuclear DNA protection that is progressively reduced as melatonin output falls with age.
Supplementation: What the Evidence Shows
Low-dose melatonin, 0.5 to 1 mg taken 30 to 60 minutes before desired bedtime, is supported by reasonable evidence for improving sleep onset and sleep efficiency in older adults. The European Food Safety Authority permits the claim that melatonin contributes to the alleviation of the subjective feeling of jet lag and to normal sleep. The dose matters: higher doses of 5 to 10 mg, which are common in US products, do not produce greater sleep benefit and may produce morning grogginess via receptor desensitisation.
Sources
- Brzezinski, A., et al. (2005). Effects of exogenous melatonin on sleep: a meta-analysis. Sleep Medicine Reviews, 9(1), 41-50.
- Skene, D.J., & Arendt, J. (2006). Human circadian rhythms: physiological and therapeutic relevance of light and melatonin. Annals of Clinical Biochemistry, 43(5), 344-353.
- Pevet, P., & Challet, E. (2011). Melatonin: both master clock output and internal time-giver in the circadian clocks network. Journal of Physiology, 105(4-6), 170-182.