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Feeding 'morning' breast milk at night might hurt babies' sleep

Aug. 20, 2019
Feeding 'morning' breast milk at night might hurt babies' sleep

Breast milk is often called liquid gold for its many benefits, but the magical baby food may have one surprising side effect that few parents know about. Breast milk actually changes composition from daytime to nighttime, and using “morning milk” at bedtime could be keeping babies awake.

“[H]uman milk is a powerful form of ‘chrononutrition,’ formulated to communicate time-of-day information to infants,” says Darcy Saxbe, assistant professor of Psychology at the University of Southern California, and Jennifer Hahn-Holbrook, assistant professor of Psychology at the University of California, in their recently published theory.

According to the researchers, about 85% of breastfeeding moms have pumped or expressed their breast milk, which means babies aren’t always consuming that milk at the exact time of day it was produced. As the researchers note in their findings, breast milk that is produced in the morning may contain three times as much cortisol, a hormone that can make babies more alert. It also has more protein and amino acids to meet the physical demands of wakefulness. Conversely, “night milk” contains more melatonin, the hormone that promotes sleep.

What this means is that when babies drink “morning” breast milk during evening and late-night feedings, it’s possible that the composition of the milk can make it more difficult for them to fall asleep. This is particularly important because research has linked disruptions in infant’s sleep to an increased risk of developing colic. Sleep is also vital to memory, language, executive function and overall cognitive development.

Unfortunately, we don’t yet know exactly how much babies’ sleep might be impacted by the composition of breast milk, as the research to cement these claims is still limited. Saxbe and Hahn-Holbrook note that the limited research into this subject presents a challenge in making recommendations to breastfeeding moms. For now, the researchers recommend that parents label stored breast milk with the time of day at which it was pumped and then try to feed it to their babies within that same time period. As if moms need one more thing to worry about!

Breastfeeding already presents unique challenges to busy families, particularly if the mom has to worry about finding places to pump at work or storing breast milk for use at day care. While no one is arguing against advice that will help babies get more sleep, it may not be reasonable to expect parents to add “feeding this exact bottle of milk at this exact time” to their already crowded to-do list.

A 2009 study does back up the theory that breast milk should always be consumed at the same time of day that it’s expressed, due to the presence of hormones that “excite or relax the central nervous system.” And we already know that breast milk evolves in other ways to meet babies’ needs. When a baby is first born, nutrient-rich colostrum stimulates the baby’s digestive system to receive the nutrients in breast milk before your body starts producing it. When an infant is sick, the amount of antibodies in a mother’s breast milk increases to help them fight the illness. 

Breast milk has proven to be a highly individualized source of food for babies. Hopefully Saxbe and Hahn-Holbrook’s new additions to the existing body of breastfeeding research will prompt further studies and more concrete recommendations. 

Of course, if you do notice changes in your baby’s sleep or feeding patterns or feel that your baby is not getting adequate sleep, you should always consult with their doctor. And if you have the time to label and schedule bottles, it may not be such a bad idea. It won’t solve every sleep problem, but as any mom or dad can tell you, exhausted parents will take all the help they can get!

Read next: Protecting breast milk during power outages

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