06-29-2026
Breastfeeding may help babies develop healthier sleep patterns
Plenty of new parents reach for formula at some point, and the reason is not always about nutrition. A lot of them think that breastfed babies sleep less soundly
The belief is everywhere. Breastfed babies, the story goes, wake more often and sleep in shorter bursts because breast milk moves through the stomach so fast
It sounds logical enough. A baby who digests quickly should get hungry sooner and stir more during the night
A very large study from Japan now suggests the opposite is closer to the truth
Sleep matters a great deal in the first year of life. Lack of sleep early on has been tied to later obesity, behavior problems, and weaker thinking skills as children grow up
That is partly why feeding and sleep get tangled together in parents’ minds. People hear that formula keeps babies full for longer, and this translates to improved sleep
The World Health Organization recommends feeding only breast milk for the first six months, mainly because of its protection against infection and its long-term health perks
Even with that advice out there, the sleep worry sticks around
“WHO widely promotes breastfeeding, and most people are aware of the multiple health benefits it provides. Nevertheless, perceptions that breastfed infants sleep less, or that formula-fed infants sleep for longer periods, remain common,” said Ms. Nakagawa, the study’s first author
“We wanted to provide solid evidence to bust this misconception.”
Researchers at the University of Toyama in Japan decided to check the claim against real numbers. They turned to one of the biggest birth studies ever run
The data came from the Japan Environment and Children’s Study, a nationwide project that has been tracking families since pregnancy across 15 regions of the country
Overall, the team looked at 82,918 mother-infant pairs
Mothers filled out a questionnaire six months after giving birth, describing how they had fed their babies
When each child turned one, the parents reported how many hours the child slept
The team split the babies into four groups based on those first six months. One group received only formula the entire time
A second group was breastfed for less than six months. A third was breastfed for the full six months but also given some formula along the way
The last group was fed only breast milk, with no formula at all, for the whole six months
The National Sleep Foundation in the United States says one-year-olds should get 11 to 14 hours of sleep across a full day
The researchers treated anything under 11 hours as short sleep. With that line drawn, they could count how often short sleep turned up in each feeding group
Every group that got any breast milk slept better than the formula-only group. The pattern was hard to miss
Among formula-only babies, 12.2 percent slept too little at age one. That figure dropped to 10.2 percent for babies breastfed for under six months
Babies breastfed for the full six months with some formula landed at 9.7 percent. The babies who got only breast milk for six months did best of all – only 8.8 percent experienced too little sleep at age one.More breastfeeding, less short sleep
The team then adjusted for dozens of other things that could muddy the picture. That list included household income, the mother’s education, the baby’s own sleep at one month, and whether the child went to daycare
The gap still held firm. Exclusively breastfed babies were about 23 percent less likely to sleep too little than formula-only babies
The link also got stronger the longer breastfeeding went on. More months on breast milk lined up with a steadily lower chance of short sleep, a pattern scientists call a dose-response effect
“This study provides reassurance against the common perception that breastfed babies sleep less because breast milk is digested more rapidly,” said Ms. Nakagawa
“Our findings suggest that such concerns should not discourage parents from considering breastfeeding and its many, well-established benefits.”
So what could be driving this? The authors point to a few real differences between breast milk and formula
Formula stays exactly the same in every bottle. Breast milk, by contrast, shifts across the day and night to match what the growing baby needs
One key difference is melatonin, a hormone that brings on sleep and steadies the body clock. Breast milk carries it, and formula does not
Newborns barely make any melatonin of their own for the first couple of months. Breast milk produced at night delivers a small dose, which may help the baby start telling day from night
Breast milk also holds tryptophan, a building block the body uses to make melatonin. Its levels rise in breast milk after dark
That nightly dose could help babies settle into a regular sleep-and-wake rhythm sooner than a steady-state formula would allow
There is a third possible route, and it runs through the gut. Breastfeeding helps shape the mix of bacteria living in a baby’s intestines
Those bacteria send signals to the brain along what scientists call the gut-brain axis. A healthier gut community may support steadier sleep patterns over time
The differences here are real, though they are not huge
The widest gap between any two groups was about 3.4 percentage points, and the study leans on parents’ memories, so it cannot prove that breast milk directly causes longer sleep
Even so, the takeaway for an anxious parent is pretty clear. In this enormous sample, the fear that breastfeeding cheats a baby out of sleep simply did not hold up
The study is published in the European Journal of Clinical Nutrition
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