Human breast milk is much more than just a meal: it is also a clock that provides information to babies about what time of day it is, since the composition of breast milk changes throughout the day. In the morning energizing milk contains a different cocktail of ingredients than the calming milk at night. Researchers believe this “chronutrition” may help program babies’ developing circadian rhythm , the internal timer that allows babies to distinguish day from night.
But what happens when babies consume milk that does not come directly from the mother’s womb and that has been expressed at other times of the day or has been saved for the baby to consume at another time? Until now scientists have hardly bothered to study the possible effects of “untimely” milk consumption on infant development, but the repercussions may be vast.
As psychologists studying the biology of parenthood, we collaborate with Laura Glynn, Caroline Steele, and Caroline Bixby to investigate breast milk testing as a measure of time.
Biological clocks throughout the day
Sleep, digestion, and energy levels all display circadian rhythms, which means they follow a daily cycle. As any parent who has had to get up at 3 in the morning to wake their baby knows, babies are not born with these rhythms completely in sync. In turn, their sense of day and night develops during the first weeks and months of life thanks to cues such as sunlight and darkness.
Babies can have very different behaviors: some show fairly predictable circadian fluctuations in hormones in relation to alertness, sleep and appetite, being able to sleep for long periods of time shortly after birth, while others seem to have the rhythms diaries deranged for months. A delay in the development of the circadian rhythm can increase the risk of colic and lead to growth problems or malnutrition.
But scientists know very little about the reasons for the differences in babies’ circadian biology. Breast milk may help program babies’ circadian rhythms , helping explain why some parents of newborns can sleep through the night, while others have a hard time getting their babies used to a routine.
Milk changes
Breast milk changes significantly throughout the day. For example, levels of cortisol (a hormone that promotes alertness) are three times higher in breast milk in the morning than in the evening. Melatonin, which affects sleep and digestion, is barely detectable in daytime milk, while it rises in the afternoons and peaks at midnight.
Night milk also contains higher levels of some DNA components that help improve healthy sleep. Day milk, on the other hand, has more amino acids that promote activity than night milk. Iron in milk peaks at noon; vitamin E in the afternoon. Minerals like magnesium, zinc, potassium, and sodium are all highest in the morning.
Daytime milk could contain an entire immune concoction. Among mothers who gave scientists breast milk samples during the first month after delivery, immune components (including key antibodies and white blood cells) had higher levels during the day than at night. Another study found higher levels of an important component for immune system communication in daytime milk compared to nighttime milk.
Although it is clear that milk changes throughout the day, scientists still know little about its significance for the health of babies.
Researchers know that hormones and immune components in breast milk are passed on to babies and that babies begin to develop and refine their own circadian rhythms during the first few months of life. It’s plausible that these time-related cues in breast milk may help shape babies’ own circadian biology. The differences in breastfeeding times could explain why there are so many differences in the development of these daily rhythms from one baby to another.
Untimely messages in the milk?
For most of human history, breast milk could only be consumed directly from the womb, which meant that milk was always ingested when it was produced. Now, with breast pumps and refrigeration, this is no longer the case: according to a survey conducted between 2005 and 2007, more than 85% of breastfeeding mothers in the US had expressed their milk.
What happens when babies are fed night milk in the morning or day milk in the afternoon? We do not know for sure, since there are hardly any studies on it. Giving a baby a bottle of daytime milk in the morning, with its high cortisol levels and low melatonin levels, could be the nutritional equivalent of turning on the lights just before bed.
If the temporary cues in milk really help calibrate the circadian biology of babies, then those who are fed milk “out of time” could have more problems with sleep, digestion and development.
Of course, there is a simple way to fix it. Mothers could label their breast milk with the time of expression and coordinate when they feed their babies so that they offer milk in the morning in the morning, milk in the afternoon in the afternoon, and milk in the afternoon. nights at nights.
If it were to become standard practice in newborn intensive care units, we believe that thousands of babies could benefit from drinking milk at the right time, which could help them better regulate their circadian rhythms . Many newborn intensive care units have already adopted practices designed to improve the regulation of circadian biology in babies, such as lowering the lights at night, so breastfeeding that takes into account the time of milk production would be the next logical step to take. Similarly, milk banks that accept donor milk could batch classify milk based on time of expression.
There is a simpler alternative to having to coordinate the milk that has been expressed: improving the ability of women to breastfeed their babies directly by improving the conditions of maternity and paternity leave . Mothers who can directly breastfeed do not have to worry about organizing milk by hours of the day and offering milk directly from the breast could have other health benefits.
Science continues to explore the role of breastfeeding in internal clocks and its impact on the health and development of babies. If milk according to pumping time turns out to be a good way to set babies’ internal clocks, this is a public health issue that reflects the importance of creating measures that help mothers stay home with their children during the first year of life.
Authors: Darby Saxbe . Assistant Professor of Psychology, University of Southern California. Dornsife College of Letters, Arts and Sciences; and Jennifer Hahn-Holbrook , Assistant Professor of Psychology, University of California, Merced.
This article was originally published on The Conversation. You can read the original article here
Translated by Silvestre Urbón
Fotos | iStochphoto
