Breast milk ingredients and sleep

Behind the Headlines

Monday October 5 2009

Breast milk is the best nutrition for infants under six months

“Mums who express milk for feeding from a bottle should make sure it is given to baby at the same time it came from the breast, otherwise it could disrupt sleeping patterns,” the Daily Mail reported.

The newspaper said that researchers have found that milk expressed in the morning contains natural stimulants, but that milk expressed in the evening helps babies sleep, as it contains "calming chemical compounds”.

This study found that the concentration of certain sleep-associated chemicals fluctuate in human breast milk over a 24-hour period. However, their effect on babies was not directly examined and so it cannot be assumed that they have an effect on babies' sleep.

The lead researcher is quoted in the article as saying, "It is a mistake for the mother to express the milk at a certain time and then store it and feed it to the baby at a different time." However, the study did not investigate this and there is no evidence that this is the case.


Where did the story come from?

The research was carried out by Dr Cristina Sanchez and colleagues from the University of Extremadura, Hospital Perpetuo Socorro and St Boi de Llobregat, all academic and medical institutions in Spain.

The study was published in the peer-reviewed medical journal Nutritional Neuroscience. The research was funded in part by Laboratorios Ordesa SL and a grant from the University
of Extremadura.


What kind of scientific study was this?

The researchers in this study were interested in how the nucleotide content of human breast milk changes over a 24-hour period. These nucleotides have important functions in developing embryos, including development of the immune system, a healthy gut and healthy cells. Their potential role in affecting sleep was specifically being investigated here.

A large proportion of breast milk is protein, providing the baby with sustenance and nutrients to develop. Breast milk also contains several nucleotides, the building blocks of nucleic acids (which make up genetic material such as DNA). Some of these nucleotides have been shown to have an effect on sleep and three were of particular interest to these researchers.

5’UMP has a depressive effect on the central nervous system. Studies have shown that if it is given at night it increases the number of REM (rapid eye movement) and non-REM sleep episodes. The second, 5’AMP, is a well-documented sleep inducer. The third, 5’GMP, works with melatonin to regulate circadian rhythms (the biological clock). These, and several other nucleotides, were examined in this study.

The researchers set out to assess changes in breast milk composition over a 24-hour period. They enrolled 30 healthy Spanish mothers who had been breast-feeding for three months. Samples of breast milk were collected just before each feed over a 24-hour period between March and July. Between six and eight samples were collected from each mother.

The researchers used a technique called capillary electrophoresis to assess the composition of the milk samples. This was used to test whether there was a notable difference in nucleotide concentration depending on what time the samples were taken. A mathematical technique called cosinor analysis was then applied to the results. This is often used to examine fluctuations in measurements over time and tests whether they conform to predictable rhythms.


What were the results of the study?

The researchers found that there were increased levels of 5’AMP nucleotides during the night (in samples expressed after 8pm). The levels were at their highest earlier in the night and lessened towards pre-dawn.

The tests showed that the 5’UMP nucleotides peaked in the middle of the night. There were no variations in the concentrations of the other nucleotides during the 24-hour period. Cosinor analysis showed evidence of fluctuation in the 5’AMP, 5’GMP, 5’CMP and 5’IMP nucleotides.


What interpretations did the researchers draw from these results?

The researchers conclude that their study shows that the concentration of nucleotides in breast milk is not constant over a 24-hour period, in particular for 5’AMP, 5’UMP and 5’GMP.

They say the increase in concentrations of these nucleotides at night suggests they may be involved in “inducing hypnotic action in the infant”.


What does the NHS Knowledge Service make of this study?

This small observational study found that the concentration of certain, sleep-associated chemicals fluctuate in human breast milk over a 24-hour period. Other chemicals in the body are known to behave similarly, such as melatonin, a hormone involved in the cyclical regulation (daily rhythm) of many of the biological functions in the body.

This research was an observational study, a type of study design that can indicate associations between factors (in this case levels of nucleotides and time of day), but cannot show that a cause-and-effect relationship is present. Babies were also not included in this study so the effects of the changing nucleotide concentrations on their sleep cannot be assumed. The ingredients in human milk may be tracking (following) some other process in the mother, that is unconnected with infant feeding and sleep.

Some newspapers report that one of the researchers has recommended that babies should not be given milk that has been expressed by their mothers at a different time of day. However, this was not investigated by this study and it gave no evidence that this is the case. Further research would be needed to investigate this claim, for instance comparing sleeping patterns between babies receiving expressed milk and those not.

Regardless of these findings, breast milk is known to be nutritionally balanced for child growth and development. The World Health Organization and the Department of Health both recommend breastfeeding as the best form of nutrition for infants. If possible and if they choose to, women are advised to exclusively breastfeed for the first six months.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

For baby, a breast-milk cappuccino: Morning feed gives infants a natural pick-me-up, Daily Mail, October 3 2009 

Why breast milk helps babies sleep at night, The Daily Telegraph, October 3 2009

Links to the science

Sánchez CL, Cubero J, Sánchez J, et alThe possible role of human milk nucleotides as sleep inducers. Nutritional Neuroscience 2009; 12: 2–8


Further reading

Several Cochrane reviews consider issues to do with breastfeeding, including:

Henderson G, Anthony MY, McGuire W. Formula milk versus maternal breast milk for feeding preterm or low birth weight infants. Cochrane Database Syst Rev 2007, Issue 4


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