Mothers who use a breast pump to express milk during the day and then bottle-feed it to their baby at night may be letting themselves in for a sleepless night.
Naturally occurring chemicals called nucleotides that have previously been linked to sleepiness only reach their highest concentrations in human breast milk that is expressed at night.
Nucleotides are the building blocks of DNA, but they also participate in cellular signalling and metabolic processes within cells. Several of them have also been implicated in sleep.
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The chemicals had already been found in breast milk, their concentrations increasing in the first few weeks after birth, so it seemed likely that they are important for tissue development. Now it seems they may have an additional role.
Milk round
Cristina S谩nchez at the University of Extremadura in Badajoz, Spain, and her colleagues looked at the concentrations of 5鈥橴MP, 5鈥橝MP and 5鈥滸MP 鈥� the three nucleotides most strongly associated with sleep and sedation 鈥� in the breast milk of 30 healthy mothers who had been breast-feeding for at least 3聽months. Samples of milk were collected before each feed over a 24-hour period, with between six and eight samples collected per mother.
They found that concentrations of 5鈥橝MP were highest at the beginning of the night, while levels of 5鈥橤MP and 5鈥橴MP increased as the night wore on. These sedatives were found at much lower concentrations in milk expressed during the day.
鈥淚t 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,鈥� says S谩nchez.
She suggests that 5鈥橝MP in breast milk might be fuelling the release of the sleep-promoting neurotransmitter GABA, while 5鈥橤MP is involved in the secretion of melatonin,which helps regulate the natural body clock. 5鈥橴MP is known to promote the amount of both REM and non-REM sleep.
Since previous studies have also hinted that bottle-fed infants have more problems sleeping through the night, S谩nchez鈥檚 colleague, Javier Cubero, has been investigating whether sleep-inducing nucleotides could be added to formula milk.
In a separate study, S谩nchez and Cubero created a 鈥渘ight-time鈥� milk by adding 5鈥橝MP and 5鈥橴MP to standard formula milk. Infants receiving this milk between 6聽pm and 6聽am, and normal milk during the day, fell asleep faster and spent longer sleeping than when they drank standard formula milk all the time.
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