TOYAMA — Yuri Nakagawa and colleagues published findings on March 31, 2026, in the European Journal of Clinical Nutrition indicating that infants exclusively breastfed for six months showed a 23% lower likelihood of short sleep duration at one year of age compared to formula-fed infants.

Nakagawa, a doctoral researcher at the University of Toyama in Japan and the study's first author, and her team analyzed data from the Japan Environment and Children's Study. The study examined 82,918 mother–infant pairs to investigate links between feeding practices during the first six months of life and sleep duration at one year of age. Mothers completed questionnaires at six months regarding early feeding practices, and parents reported child sleep duration when the children reached one year.

Children sleeping less than 11 hours per day were categorized as having insufficient sleep, based on U.S. National Sleep Foundation recommendations. The study divided infants into four feeding groups: exclusively formula-fed, breastfed for less than six months, breastfed for six months with formula supplementation, and exclusively breastfed for six months.

The risk of insufficient sleep at age one for babies exclusively breastfed for the first six months was 8.8%. In comparison, infants fed only formula for the first six months had a 12.2% chance of short sleep. The risk of short sleep was 10.2% for infants breastfed for less than six months and 9.7% for infants breastfed for six months with formula supplementation. The study identified a graded association, where longer breastfeeding duration correlated with a progressively lower likelihood of short sleep, even after adjusting for maternal, infant, and environmental factors.

Nakagawa addressed common perceptions regarding infant sleep and feeding. "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," Nakagawa said. "This study provides reassurance against the common perception that breastfed babies sleep less because breast milk is digested more rapidly," she added.

Breast milk contains substances such as melatonin and tryptophan. Melatonin is secreted into breast milk at night, and tryptophan concentrations in breast milk are higher during the night. "Our findings suggest that such concerns should not discourage parents from considering breastfeeding and its many well-established benefits," Nakagawa said.