It's commonly believed that one of the sacrifices new moms must make in order to breast-feed is their sleep. But new research suggests that's just not the case.
The study, published in the journal Pediatrics, found that new mothers slept about the same amount of time whether they were breast-feeding or formula-feeding.
"There is some small evidence that infants who are breast-fed sleep less, but no one has ever looked at the mother's sleep," said the study's lead author, Hawley Montgomery-Downs, an assistant professor of psychology and coordinator of the behavioral neuroscience program at West Virginia University in Morgantown.
"But, we found absolutely no difference in the mother's sleep based on how babies were fed," said Montgomery-Downs.
Why babies don't sleep
New parents know - or soon learn - that sleep is something they just won't be getting enough of, for at least a few months. During those first few months, the baby's digestive system simply isn't mature enough to hold enough food to keep the baby sated for more than a few hours at a time.
Because breast milk is more easily digested, babies who are breast-fed generally wake up to eat more often than formula-fed babies.
"Women sometimes use the rationale of wanting and needing more sleep as a reason not to breast-feed, but breast-feeding is so important for both the mom and the baby's health, we wanted to determine whether formula- or breast-feeding would have an effect on maternal sleep," Montgomery-Downs said.
And, she added, the researchers realise that women shouldn't simply be told to get by with less sleep because it's good for the baby. A lack of sleep can have significantly detrimental effects on a new mother, and may even contribute to post-partum mood disorders, according to background information in the study.
"We wanted to have more empirical evidence and hopefully be able to come up with better strategies for women," Montgomery-Downs said.
Formula and breast milk
The study included 80 women: 27 who breast-fed exclusively for at least 12 weeks, 18 who exclusively formula-fed for at least 12 weeks and 35 who used both methods of feeding.
The women kept sleep diaries and reported on the quality of their sleep and the number of times they woke up during the night. They also wore devices that measured nighttime sleep, and reported when they were feeling sleepy during the daytime.
The researchers found no significant differences in sleep between the three groups of women.
"I'm not in a position to say exactly why there was no difference, but women who breast-feed may not have the same arousal levels as women who have to get up and prepare formula. It may be that breast-feeding moms are just staying in the dark, and are able to get back to sleep faster," Montgomery-Downs said.
Breast milk contains the hormone prolactin, which may have a sleep-inducing effect on the baby, she added.
Breast milk metabolised faster
Shelby Harris is director of the behavioural sleep medicine program at the Sleep-Wake Disorders Center at Montefiore Medical Center in New York City. She said: "Breast-fed babies do wake up a little bit faster because they metabolise the milk faster, and it's always been assumed that moms wake up more, too. And, a lot of women give up on breast-feeding because they think formula will help them sleep more."
But, she added: "The American Academy of Pediatrics recommends breast-feeding, so consider the risks and benefits of breast-feeding versus formula-feeding and see if you can work it into your life. But, don't go with the old thinking that you'll sleep better if you formula-feed. The first couple of months are going to be tough, regardless of which feeding method you choose, so think about other things, like the health of your baby."
Montgomery-Downs said, "Breast-feeding benefits the infant and mother, and better sleep can't really be used as a reason to wean your baby, because your sleep won't be benefited by stopping breast-feeding."
What might help, she said, is figuring out how to get more consolidated sleep. Scheduled feedings can help, as can expressing breast milk, and having someone else take a feeding or two to allow you to get a longer block of sleep at once, she added.
The good news from another recent Pediatrics study is that most babies will start sleeping longer, possibly even through the night, between two and four months of age.
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