Let’s Face It: Formula-Fed Babies Sleep Better

Breastfed babies tend to arouse from sleep more easily and sleep for shorter periods of time. Nearly all babies who sleep through the night by 3 months are formula-fed.

Breastfeeding is a major battleground of the modern mommy wars. In her widely discussed piece in The Atlantic, Hanna Rosin called breastfeeding the “new sucking sound”–replacing vacuuming as the task that shackles women to the house, promotes the unequal distribution of childcare and household duties, and prevents women from reaching the upper echelons of professional success. The benefits of breastfeeding have been oversold, she claims, and–just as significantly–the costs to women’s sleep, time, and career progress have been downplayed.

On the other side of the debate, the American Academy of Pediatrics states that the benefits for the infant in terms of reduced risk of infection, adult obesity, allergies, and asthma are so great that breastfeeding must be viewed as an “investment in your child’s future” rather than a “lifestyle choice.” Some lactation consultants fall into this camp too, needing to be reminded to suppress their impulse to sigh when yet another mother complains of exhaustion and lack of sleep, for fear they alienate her–and fail to convince her to keep breastfeeding.

On both sides, well-intentioned but overzealous advocates twist the evidence on breastfeeding, cherry-picking among studies to support their preexisting views.

This is especially true when it comes to one of breastfeeding’s major downsides: disrupted sleep.

Consider the post, 5 Cool Things No One Ever Told You About Nighttime Breastfeeding, which claims that the number 1 coolest thing about nighttime breastfeeding is “breastfeeding moms actually get MORE sleep than their formula-feeding counterparts,” and concludes with the rhetorical question: “Did you ever think, when you hear your baby rouse at 2:00am, that they are actually giving you the gift of MORE sleep…?”

To which I would like to respond: No, never, not only because it does not square with my own experience, but also because the research on this topic is clear: breastfeeding moms, on average, get less sleep, not more.

Almost without exception, studies on formula feeding, breastfeeding, and sleep find that breastfed babies wake up more often than formula fed ones at night, and breastfeeding mothers therefore get LESS uninterrupted nighttime sleep.

Nighttime Wakings in Formula-Fed Versus Breastfed Babies

2003 study, in which researchers followed 253 newborns for their first 3 months of life, is a case in point. Parents reported their feeding practices (formula, breast, or a combination) while tracking how frequently their babies awoke in the middle of the night.

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Two-thirds of the babies in the study slept through the night at the end of the third month–almost all of these babies (94%) were formula-fed. While 79% of formula-fed 3-month-olds in the study slept through the night, only 15% of breastfed 3-month-olds did.

This 2003 study is small. So by itself it would not be terribly compelling. But scores of other studies find the same pattern: breastfed babies spend less total time sleeping and wake up more frequently at night. Some studies even find formula-fed babies sleep more at night than breastfed babies as early as four weeks of age.

The evidence is strongest, though, for older babies. Breastfed babies and even nursing toddlers are more likely to wake up to feed in the middle of the night. Much more likely. According to a recent Australian study of 4,507 babies, at 6 months of age, breastfed babies were 66% more likely to wake up in the middle of the night. (See additional studies here and here.) The evidence is so strong infant sleep researchers generally state formula-fed babies’ longer nighttime sleep as a fact.

The Evidence Cited By Breastfeeding Advocates

Only two studies deviate from this general pattern. In the first, researchers measured how much nighttime sleep 133 mothers were getting at 3 months postpartum. Exclusively breastfeeding mothers slept 45 minutes longer at night, on average, than did mothers who formula fed or supplemented with formula.

In the second study, researchers compared the nighttime sleep of 19 mothers who were 9-16 weeks postpartum and 61 mothers who were 2-13 weeks postpartum. No significant differences were found in sleep duration or self-reported fatigue between formula and breastfeeding mothers. Breastfeeding mothers did tend to report less sleep, but the difference was not statistically significant.

These two studies are small and inconsistent with the rest of the research. Their findings may simply be anomalies. On the other hand, unlike the rest of the research, these two studies focus on mothers’ sleep rather than babies’ sleep, and this could be why they do not find much of a difference between the formula-feeding and breastfeeding mothers. Most newborns, formula or breastfed, wake to feed at night. Formula obviously takes longer to prepare than breast milk. So when their babies do wake up, formula feeding parents end up being awake for longer and getting less total sleep.

In response to the second of these two studies, a pediatrician wrote in to make the same argument :

Dear Authors,

I appreciate your study in this area however your conclusions do not represent my personal practice experience. I have spoken with thousands of mothers; perhaps you would have a different conclusion if your sample size was bigger.

Newborn feeding patterns are similar initially. Mothers that breast feed have at least one to two night time feedings from 2 to 12 weeks. However, by about 8 to 10 weeks formula fed babies that can eat at least 6 oz with 4 daytime feeds can sleep a solid 12 hours at night. I have seen this pattern hundreds of times. Mothers that have a formula fed infant that follow the above pattern are much more rested.

Even though breastfeeding is more time intensive and more sleep depriving it is far superior to formula and I highly recommend it to all of my moms…

But why do formula-fed babies sleep for longer stretches and wake less frequently at night?

When I’ve brought up these findings, a number of people responded, “Well, of course, breast milk is less filling than formula.” This is the most commonly offered explanation: breastfed babies become hungrier sooner and therefore wake up in the middle of the night to feed. And it’s true: breast milk is digested more quickly than formula. For newborns, staying full for longer stretches may help them sleep for longer periods of time.

But here’s the thing: breastfed babies continue to wake up more frequently throughout their first year and into toddlerhood. By 6 to 9 months of age, babies’ stomachs have increased in capacity, and most are eating solid foods. Why are they still waking up?

One possibility is that breastfeeding mothers tend to nurse their infants back to sleep. A large study of just over 10,000 babies found that breastfed babies woke up more at night, but only if they were nursed back to sleep. Unfortunately, this study was cross-sectional, so it cannot tell us whether night nursing causes night wakings or is caused by them.

One recent clinical trial does suggest that night nursing causes night wakings. Beginning when their babies were 2 weeks of age, an intervention group of exclusively breastfeeding parents was instructed to offer a focal feed sometime between 10 pm and midnight. If the newborn woke up again before morning, the father was to attempt to soothe the baby by re-swaddling, changing diapers, and walking–basically, by any means possible save feeding, to gradually lengthen the time between nighttime feeds. By 8 weeks of age, 100% of breastfed infants receiving the intervention (compared to 23% in the control group) were “sleeping through the night.”

(I was very excited by this study until I read the fine print. Only by the painfully low standards of new parents could these newborns be said to “sleeping through the night”, which was defined as not waking up between midnight and 5:00 a.m.)

Sleep Benefits of Breastfeeding

There are some sleep benefits associated with breastfeeding. Breast milk’s unique hormones and proteins appear to directly affect infant sleep patterns. Breastmilk contains numerous sleep-promoting hormones and proteins, such as melatonin, delta-sleep-inducing peptide, tryptophan, and prolactin, among others. The release of these hormones and proteins tracks the mothers’ own circadian rhythm and may help entrain newborns’ own circadian rhythms, helping them distinguish between daytime and nighttime.

(Note to new mothers who are pumping: night milk is not the same as day milk!)

Perhaps because of these sleep-promoting hormones, breastfed babies also arouse more easily from active sleep. This tendency probably contributes to breastfed babies’ lower risk of SIDS, but likely also makes them more prone to night waking.

To handle fragmented sleep, nature appears to have provided nursing mothers with some recompense. Despite formula-fed infants waking up less in the middle of the night, nursing mothers benefit from high levels of sleep-inducing hormones like prolactin, experience more than double the normal duration of nocturnal slow wave sleep, and may be able to sleep during night-time feeds, particularly if co-sleeping.

What Is The Natural Sleep Pattern For Babies?

It is hard not to look at the evidence and conclude that, much to the dismay of exhausted parents, nature did not intend for babies to reliably sleep through the night. Evolutionary psychologists have even argued that infants nurse at night to prevent their mothers from becoming pregnant again. A younger sibling uses up precious resources, threatening the baby’s health and survival.

The mother’s reproductive fitness is in conflict with her baby’s fitness, according to this theory. A mother’s reproductive fitness is maximized by having relatively short intervals between births (the risk of child mortality is higher, but a larger total number of children survive). But the baby’s survival is maximized by a long interval between his or her birth and the next birth.

The Bottom Line

Natural or not, breastfeeding usually entails many additional months of broken sleep, and a prolonged period of broken sleep can make caring for a new baby, returning to work–and just about every aspect of existence–pretty miserable. As I can personally attest, suffering through months of broken sleep is not only about fatigue or a mild mental fogginess that can be masked by an extra cup of coffee–or four. Consistently poor sleep heightens hostility, clouds our thinking, adds stress to the already major stress of caring for a baby and–not surprisingly–increases the likelihood of postpartum depression. These problems are bad for mothers and bad for our babies.

So yes, women should certainly be told about the positive effects of breastfeeding. But it is offensive, paternalistic, and intellectually dishonest to provide false or cherry-picked information on breastfeeding’s downsides. These downsides exist. And no one benefits from brushing them under the rug.

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Author: Amy Kiefer

I am a research scientist and mother of three munchkins. I live in the Bay Area and when I am not child wrangling and catching up on lost sleep, I love digging into the research on all things fertility, pregnancy, and breastfeeding related.

11 thoughts on “Let’s Face It: Formula-Fed Babies Sleep Better”

  1. This was a really interesting post. I have a personal theory that a big part of the difference between breast and bottle feeding at night is actually due to the bottle, not the use of formula.

    For the most part I pumped while bottle feeding over night (not as bad as it sounds, you can do them both at once), because the baby slept much better than when I tried to breastfeed directly. A couple other people I know independently settled on the same system for the same reason. When I tried to breastfeed at night my baby would fall asleep so fast that I don’t think she was actually eating very much, so my best guess is that the better sleep was due to her eating more per feeding.

    I wish someone would do a study on this! It would be so interesting to see how the sleep habits of formula fed babies compare to those of babies who are bottle fed breast milk.

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    1. That’s really interesting. Your experiences square with my own. For our two, it seemed like breastfeeding from the breast was super rewarding. So rewarding that they would wake up earlier and earlier if they got to breastfeed first thing in the morning. Neither were that into the bottle. Maybe I should have pumped at night from the beginning 🙂

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  2. Oh dear, I’m commenting again.

    I’d be far more interested in studies that measured the parenting ‘styles’ as well as the data on sleep for formula vs breastfed..

    For example, I would suggest breastfeeding for a longer period of time may go hand-in-hand with parents who either co-sleep or have the baby in their room for far longer than those who formula feed. A generalisation, but unless the study included it, how do we know?
    Surely for these studies to be accurate, they have to include many other factors. Even something like expectations of when the baby would sleep through the night. I had an expectation that was what our family needed to stay sane, so I tried solutions until we *kindof* achieved that goal (no-ones baby sleeps through the night 365 days a year right!)
    How many of either tried other ways of resettling rather than a feed (formula or breastmilk) I know I probably would have tried dropping night feedings far earlier if I’d been using formula. And I dropped them relatively early & met almost immediate success at sleeping (properly, like 11 hours) through the night. It’s a lot more stressful to attempt to not breastfeed than to not prepare a bottle until you really feel they aren’t going to settle. Most of my breastfeeding friends that have babies that are waking at night, admit themselves they aren’t ready to cut the night feedings.

    Or what about whether there are single parents vs couples parenting these babies? Or even further, does the dad get up? Again, I couldn’t have dropped night feedings without a husband who was willing to get up a few times a night for a few nights (& his reward? Oh so much more sleep!!)

    Surely that’s only the start of the probable differences that may have patterns, and some of them are such subtle things..
    Even on the opposite side, do the breastfeeding mothers sleep longer because they generally try to make healthier choices which may contribute to their amount of sleep? Although I doubt this because many formula feeding mothers are equally, if not more healthy! But how do we know without these factors being included in a study?

    Honestly though, this is a great article, it gets the brain wheels turning for sure.

    Speaking of cherry-picking, although I breastfed #1 until he was 1 year old, I did not enjoy much of it at all. There is not one bit of me that misses it. I’m not sure #2 is going to get to a year if it’s the same second time around. Theres plenty of benefits but I think you have to be pretty committed & rid the ‘fairy-tale’ to actually continue breastfeeding when its not something you love. I do feel some friends simply had no stickability & gave up because it was harder than they expected.. In which case, we should have helped with their expectations & said that, quite frankly, although it’s great for your baby, it can also be a totally crap experience for you!

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    1. I have not seen any studies on parenting styles and sleep, but I think you are right, part of the reason breastfed babies wake up more often is that their mothers often feed them to sleep. Oh, those sleep associations. Once formed, they can be so hard to break. With my second I was very careful to put her down drowsy but awake as often as possible from about a month on, so we never had to do full on sleep training. My husband, like yours, just had a few nights of giving her a bottle of water to get her drop her night feeds around 5 months.

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  3. I would also chime in that preparing a bottle at night takes more time than opening your nursing cami (or whatever you’re wearing) and sometimes the baby self settles before the bottle is ready. My second baby who is 4 months old (3 months corrected age) doesn’t like her formula cold and so, has to wait until it is warmed up. About half the time, by the time I would do that she has fallen back asleep. I feel like the act of preparing a bottle has forced her to learn to self soothe sooner than if we were nursing. She sleeps 7 hours at least at night now, sometimes longer if her daytime intake was good. My first daughter breastfed at night and she did not sleep through the night even once until close to 6 months. We coslept with her also.

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  4. Thank you for this. I had to stop nursing altogether and start pumping and supplementing with formula due to a severe early case of PPD/PPA brought on by the sleepless nights of breastfeeding in the early weeks. It was difficult to “give in” to formula at first but it was encouraged by my doctor as well as my LO’s ped in an effort to help protect MY sleep. So many studies and brochures and lectures are based on how BFing is best for baby and completely neglect the other side of the equation, the mother. I learned that my needs are just as important as my baby’s and caretaking required a rested mom.

    Our solution was to do formula at night and pump-to-feed during the day. Those who say that “formula makes your baby sleep longer” is a myth are probably just trying to sell you on exclusively BFing because our LO slept in 4-hr stretches once we introduced it at 12 days old and she started sleepin longer stretches by 2 months. Sleep is the most important thing to a new mom, especially one on the verge of PPD. My ped firmly believes that a sleep-deprived parent is a risk to an infant.

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