While discussing baby’s sleep with fellow moms, you’ve probably heard the idea that formula-fed babies tend to be better sleepers — dozing for longer stretches at night than their breastfed counterparts. But is there any truth to this notion, or is it nothing but a tempting tale for sleep-deprived nursing moms?
The thought behind formula’s sleep-inducing powers is that breast milk is easily and quickly digested by babies, making for more cycles of hunger and satiety throughout the night, while formula’s greater staying power keeps the tummy fuller for longer periods. There is some truth to this: formula is harder for babies to break down, moves more slowly through the digestive system, and uses up more energy in doing so.
Indeed, some studies show that moms with breastfed infants report waking up more at night than those with formula-fed babies, and one study of preterm infants found that those who were bottle fed woke less frequently overall. There is reason to think that formula affects a baby’s “sleep architecture,” (the pattern and structure of sleep) with formula-fed babies spending proportionally more time in REM, while breastfed babies spend more time in non-REM.
But overall, the link between good sleep and formula feeding is weak. For every study noting its soporific effects, there’s at least one countering the idea. For example, in a recent study, researchers had new moms wear a wrist actigraph to objectively measure sleep around the clock and found that exclusively breastfeeding moms slept just as much and felt equally rested (or drowsy) as moms who were exclusively formula-feeding or doing a mixture of both. Another study using the same methods found that breastfeeding parents got about 40 minutes more sleep per night. And contrary to popular belief, rice cereal before bed doesn’t help a baby sleep either.
Though the commonly held belief is that formula tends to help baby snooze, breast milk may actually be the one with sleep-inducing properties. Scientists have seen that it contains certain nucleotides (the building blocks of proteins) that are connected to mom’s circadian rhythm and could have a hypnotic effect in babies. And the boost in prolactin (which peaks at night) has been associated with important slow wave sleep for mom.
Another way to look at this question is to consider that it might not be a question of formula vs. breast milk. The drowsy formula myth comes in part from a misunderstanding about infant sleep — namely, that waking up equals hunger. This is true for the first couple of months, when young babies with tiny bellies need to eat frequently and wake up to do so. But around three or four months of age, infants go through surges in brain development that make them more aware, engaged, and ready to practice their new skills in the wee hours. Babies start to wake up more because of their primed and excited brains than their empty stomachs.
This isn’t to say that older infants aren’t hungry at night, especially if they’re used to being fed. But it’s still only one of many reasons to call out for mom. A breast, a big bottle of formula, a hefty meal of cereal — none of these will change that fact.
Heather Turgeon is a psychotherapist and science writer. She authors the weekly “science of kids” column for Babble and is a regular contributor to Strollerderby. Follow the science of kids to keep up with the latest research in child development and parenting.
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