Breast milk, best sleep: Nationwide Japanese study finds
Japanese study of more than 82,000 children finds that breastfed infants are less likely to have short sleep at age one
Toyama Regional Center for the Japan Environment and Children's Study, University of Toyama
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A large Japanese study of more than 82,000 children found that breastfed infants were less likely to experience short sleep at age 1
view moreCredit: University of Toyama
The World Health Organization (WHO) recommends exclusive breastfeeding for the first six months of life because of its many proven benefits, including protection against infections and support for healthy long-term development. However, perceptions that breastfed infants sleep less or require more frequent feeding than formula-fed infants remain common among parents and caregivers. Short sleep duration during infancy has also been linked to obesity, behavioral problems, and poorer cognitive performance later in life. Therefore, adequate sleep during this period is considered important for healthy physical and psychological development. Although infants are known to gradually develop longer and consolidated sleep periods, some caregivers choose formula feeding partly based on concerns about their child’s sleep.
To better understand the relationship between infant feeding and sleep, Ms. Yuri Nakagawa, a doctoral researcher at the University of Toyama, Japan, and colleagues analyzed data from the nationwide Japan Environment and Children's Study (JECS), one of the world's largest birth cohort studies. The study examined 82,918 mother–infant pairs to investigate whether feeding practices during the first six months of life were associated with sleep duration at one year of age. The findings were published in the European Journal of Clinical Nutrition on March 31, 2026.
“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. We wanted to provide solid evidence to bust this misconception,” says Ms. Nakagawa, the study's first author.
The mothers were given questionnaires at 6 months asking about the feeding practices they followed during the first six months for their babies. The children were then divided into four groups according to their feeding method. The first group consisted of infants fed exclusively with formula. The second group included infants who were breastfed for less than six months. The third group included infants who were breastfed throughout the six-month period while also receiving formula supplementation. The fourth group consisted of infants who were exclusively breastfed for six months. When the children reached one year of age, parents completed another questionnaire reporting their child's sleep duration. Children sleeping less than 11 hours per day were considered to have insufficient sleep, based on the U.S. National Sleep Foundation recommendations.
All groups that received breastmilk showed lesser chance of insufficient sleep compared to exclusively formula-fed infants. While infants who received only formula for the first six months had a 12.2% chance of having short sleep, the risk in infants breastfed for less than 6 months was only 10.2%. When breastfed for the entire six months and supplemented with formula, the risk further fell to 9.7%. The least risk of insufficient sleep at age one was for babies exclusively breastfed for the first six months, at 8.8%. After adjusting for a wide range of maternal, infant, and environmental factors, infants who were exclusively breastfed for six months had a 23% lower likelihood of short sleep duration compared with those fed only formula. The findings also showed a graded association, with longer breastfeeding duration associated with a progressively lower likelihood of short sleep.
“This study provides reassurance against the common perception that breastfed babies sleep less because breast milk is digested more rapidly,” says Ms. Nakagawa. “Our findings suggest that such concerns should not discourage parents from considering breastfeeding and its many well-established benefits,” she adds.
The researchers proposed several possible explanations. While the nutritional composition of formula remains relatively constant, that of breast milk adapts to the changing needs of the infant. To help establish and regulate the baby's internal clock and sleep–wake cycle, melatonin—a hormone that promotes sleep onset and improves sleep quality—is secreted into breast milk at night. Because newborns produce only small amounts of their own melatonin, breast milk-derived melatonin may help support the development of healthy sleep rhythms. In addition, breast milk contains tryptophan, an amino acid used to produce melatonin. Interestingly, tryptophan concentrations in breast milk have also been found to be higher at night.
Furthermore, growing evidence supports the gut–brain axis, a communication network linking intestinal bacteria and brain function. Breastfeeding is known to positively influence the development of a healthy infant gut microbiome. Differences in gut microbiota between breastfed and formula-fed infants may also contribute to the development of healthy sleep–wake patterns and sleep quality.
Reference
DOI: http://doi.org/10.1038/s41430-026-01718-1
About University of Toyama
The University of Toyama located in Toyama Prefecture, Japan is comprised of 3 former national universities; Toyama University (founded in 1949), Toyama Medical and Pharmaceutical University (founded in 1975) and Takaoka National College (founded in 1983), which were integrated in October 2005. This integrated university houses 9 schools, 8 graduate schools, the University Laboratory, Hospital, and Library, among others like the Organization for International Education and Exchange. There are approximately 9,300 students (including 300 international students) studying at the university.
Website: https://www.u-toyama.ac.jp/en/
About Ms. Yuri Nakagawa from University of Toyama
Ms. Yuri Nakagawa is pursuing doctoral work in Life and Clinical Medicine at the Department of Public Health at the Faculty of Medicine, University of Toyama, Japan. She is also affiliated with the Toyama Regional Centre for the Japan Environment and Children's Study (JECS) at the University of Toyama.
Journal
European Journal of Clinical Nutrition
Method of Research
Observational study
Subject of Research
People
Article Title
Breastfeeding and children’s sleep duration at 1 year of age: A nationwide birth cohort - The Japan Environment and Children’s Study
Breastfeeding may protect against ADHD symptoms
A new study from the University of Bergen shows an association between breastfeeding up to six months of age and a reduced risk of ADHD symptoms from ages three to eight.
Breast milk is the primary source of nutrition for infants. It is uniquely tailored for the child and contains numerous components beneficial for growth and brain development, including long-chain fatty acids, amino acids, antibodies, and beneficial bacteria.
“It is well established that psychiatric symptoms and disorders can be influenced by both genetic and environmental factors,” says Berit Skretting Solberg, psychiatrist and researcher at the Department of Biomedicine, University of Bergen, and senior consultant at Betanien Hospital.
There has been considerable scientific interest in understanding how breast milk and breastfeeding affect brain development and the infant immune system.
Together with her co-authors, Solberg therefore examined the relationship between the number of months an infant is exclusively breastfed (up to six months of age) and the child’s risk of developing ADHD symptoms.
Less ADHD symptoms at ages three, five, and eight years
The study used data from 37,600 families participating in the Norwegian Mother, Father and Child Cohort Study (MoBa).
Mothers reported, through a questionnaire six months after birth, the duration of exclusive breastfeeding, partial breastfeeding, and the introduction of other liquids or solid foods. These data were used to calculate the number of months each child was exclusively breastfed.
“We found that the longer a child was exclusively breastfed (up to six months), the lower the level of ADHD symptoms at ages three, five, and eight years,” says Solberg.
The association was observed in both boys and girls and was strongest at ages three and five, and somewhat weaker at age eight. All breastfeeding showed an effect, but the effect increased with the duration and intensity of breastfeeding and was strongest with exclusive breastfeeding up to six months.
Clear but moderate effect after adjustments
ADHD is partly explained by genetic factors. For example, it is known that mothers with ADHD symptoms tend to breastfeed less than others and are more likely to have children with ADHD symptoms. At the same time, children with ADHD symptoms may be more difficult to breastfeed.
“This may partly explain the relationship between lower breastfeeding and increased ADHD symptoms in children,” says Solberg.
To better understand possible causal relationships, the study adjusted for known genetic risk of ADHD and sociodemographic factors. Sibling analyses were also conducted, comparing different breastfeeding patterns within the same family.
“Even after these adjustments, there was a clear but moderate protective effect of the duration of exclusive breastfeeding on later ADHD symptoms,” Solberg explains.
More research needed to clarify causality
Solberg notes that the MoBa study is not fully representative of the Norwegian population. Participants tend to have higher education levels and are more likely to breastfeed, and to do so for longer than the general population.
She therefore does not rule out the possibility that the effect could be even greater in groups where breastfeeding is less common.
“As with other observational studies, it is difficult to draw firm conclusions about causality,” says Solberg, emphasizing the need for further research.
At the same time, she notes that the findings suggest that factors beyond genetics may influence ADHD risk:
“In our society, heredity is likely the strongest risk factor for ADHD. However, since ADHD—like other neurodevelopmental disorders—is influenced by multiple factors, our study suggests that the extent of breastfeeding may also help protect against the development of ADHD symptoms in young children.”
Read the full article:
https://www.sciencedirect.com/science/article/pii/S000632232601348X?via%3Dihub
Journal
Biological Psychiatry
Method of Research
Data/statistical analysis
Subject of Research
People
Article Title
Breastfeeding and Development of Attention-Deficit/Hyperactivity Disorder Symptoms Across Childhood
Article Publication Date
19-Jun-2026
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