Can a glass of warm milk help you sleep better in the arms of Morpheus? The Détecteur de rumeurs wondered if the research confirmed this recipe shared from generation to generation.

Taken directly from the  Government of Quebec website
Author:  Agence Science Presse –  Catherine Couturier

Medically reviewed by Marie-Lyssa Lafontaine, medical student, urology axis, University of Montreal, on 11/28/2022

Few studies

Each culture has its tricks for inducing sleep: in the West, the glass of hot milk has had this reputation for a very long time. Yet very few researchers have attempted to verify this claim. In fact, no clinical studies have examined the effects of “ordinary” milk, without additions, on sleep: interest has generally focused on milk with added ingredients.

For example, a study conducted in 1972 evaluated the effect of Horlicks, a malted milk hot drink powder. The authors concluded that participants who consumed this beverage before going to bed moved less in their sleep. But this study was only conducted on… 4 participants.

Another research, conducted in 1980, compared Horlicks to 3 other drinks: a flavored drink, a placebo and a glass of milk. Unlike the Horlicks-based brew, which caused fewer sleep disruptions, drinking milk had no effect.

Other studies have looked at the effectiveness of milk with added honey, or milk naturally enriched with melatonin (obtained when cows are milked in the evening). A 2016 New Zealand study concluded that milk enriched with melatonin, recognized as the sleep hormone, seemed to have beneficial effects in people with insomnia. However, it should be kept in mind that this study was funded by the manufacturer of fortified milk and by the New Zealand dairy industry.

Origin of the rumour: tryptophan?

Why then is it still thought that hot milk can replace counting sheep?

These soporific properties are often attributed to tryptophan, an amino acid found in milk. This amino acid is essential for the production of serotonin, a neurotransmitter that controls our moods and which can then be transformed into melatonin. Therefore, tryptophan is required for the production of melatonin, the hormone well known for its sleep-promoting effects. 

Tryptophan supplements can also be prescribed for insomnia. But in terms of milk, the dose of tryptophan contained in a glass would not be high enough to promote sleep. In addition, experts question the ability of tryptophan in milk to cross the blood-brain barrier which isolates the brain from unwanted substances carried by the bloodstream.

In fact, several nutritional studies suggest that it’s diet in general and the habit of eating in the evening or not that could have an influence on sleep — rather than specific foods.

Finally, it is not impossible that it is quite simply the comforting effect of hot milk, reminiscent of childhood, which helps to fall asleep…

Verdict

[Milk and the tryptophan it contains naturally have no direct effect on sleep. But unless you’re lactose intolerant, there’s nothing wrong with having a warm glass of milk before bed for its comforting effects.

About the Détecteur de rumeurs

Détecteur de rumeurs articles are written by science journalists from Agence Science-Presse . The Fonds de recherche du Québec and the Bureau de coopération interuniversitaire are partners in the Rumor Detector.

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