The science of melatonin. Part 2: the research

This article is part of a collection inside The Possums Sleep Program called Deeper Dive, which explores the complex scientific, historical and social contexts in which families and their babies or toddlers live and sleep. You don't need to read Deeper Dive articles to be helped by The Possums Sleep Program.

Here is more research showing why dimming the lights is not likely to help with baby or toddler sleep.

Melatonin research findings	Comment
Melatonin levels are almost undetectable at birth. A melatonin rhythm becomes measurable in blood serum from about three months of age.	The sleep of very young babies can be quickly entrained to align with the parents' circadian clock (even though they will still wake in the night), using the environmental cues of light and activity. This rapid alignment with night and day occurs with formula fed babies too, even though formula supplementation doesn't contain melatonin.
Studies (including in rats) show that removing the pineal gland has no effect on sleep, even though plasma melatonin becomes mostly undetectable.	It's not established that melatonin is required for sleep.
Damage to the suprachiasmatic nucleus (the SCN or master body clock) leads to a loss of the majority of circadian rhythms.	It’s not been established that melatonin affects the activity of the body clock. Yet the effect of light and dark on the SCN is required for a circadian sleep rhythm, even when the pineal gland has ongoing capacity to synthesise and secrete melatonin.
Winter has longer duration of melatonin secretion.	There is no evidence to suggest that children sleep for significantly longer durations in winter than in summer.
Melatonin levels show large interindividual variation, and vary according to biological sex. An individual's profile is highly reproducible from day to day.	This suggests that dose-dependent effects of endogenous melatonin are unlikely.
Living in dim light increases sensitivity to light, and circadian desynchrony alters light perception.	This suggests that light, rather than melatonin levels, drive sleep.
Melatonin levels peak in pre-adolescent children, between three and six years of age, and decrease throughout adolescence and adulthood. At 90 years of age or more, melatonin levels are less than 20% of young adult concentrations.	Elderly adults are not getting less than 20% of the sleep of young adults, which again suggests that melatonin doesn't drive sleep.
Melatonin production is associated with the onset and offset of sleep, but there are few associations between melatonin and sleep stages.	This suggests that dose-dependent effects of endogenous melatonin are unlikely.
Sleep deprivation does not eliminate the melatonin rhythm.	Endogenous melatonin continues to be produced even when an individual has not been sleeping.
There is no evidence that blind people produce different amounts of melatonin compared with sighted people, though light information typically doesn't reach the SCN in blindness.	This suggests that melatonin doses do not drive sleep.
In nocturnal mammals, melatonin is secreted during the active period at night.	This suggests the melatonin does not induce sleep.
Bradford et al 2023 found no difference in a descriptive retrospective study of pain and sedation scores in 55 patients under 12 months of age who were given melatonin for sleep promotion in an intensive care unit, though the providers gave the intervention group less opiods.	This suggests melatonin supplements do not induce sleep in infants. There are many questions raised by this study about the interpretation of infant behaviours.

Recommended resources

Will dim lights in the evening increase melatonin and make sleep easier for your baby?

Will dim lights in the evening increase melatonin and make sleep easier for your toddler?

The science of melatonin part 1: infant sleep

The science of melatonin part 3: breast milk and 'mistimed' breast milk

Selected references

You can read the article and its citations, which was used to create the table above, here.

Bradford C, Miller J, Harkin M, Chaaban H, Neely S, Johnson P. Melatonin use in infants admitted to intensive care units. Journal of Pediatric Pharmacology and Therapeutics. 2023;28(7):635-642.

Egeli TU, Tufekci KU, Ural C. A new perspective on the pathogenesis of infantile colic: is infantile colic a biorhythm disorder? Journal of Pediatric Gastroenterology and Nutrition. 2023;77(2):171-177.

Garofil F, Franco V, Accorsi P. Fate of melatonin orally administered in preterm newborns: antioxidant performance and basis for neuroprotection. Journal of Pineal Research. 2024;76:e12932.

Givler D, Givler A, Luther PM. Chronic administration of melatonin: physiological and clinical considerations. Neurology International. 2023;15:518-533.

Hausler S, Robertson N, Golhen K. Melatonin as a therapy for preterm brain injury: what is the evidence? Antioxidants. 2023;12:1630.

Tordjman S, Chokron S, Delorme R. Malatonin: pharmacology, functions and therapeutic benefits. Current Neuropharmacology. 2017;15(434-443).