Breastfeeding during the first 6 months of life may be associated with a lower likelihood of short sleep duration among 1-year-old infants, according to a recent study.
Investigators analyzed data from the Japan Environment and Children's Study, a prospective nationwide birth cohort that enrolled pregnant women from 15 regions of Japan between January 2011 and March 2014. The analysis included 82,918 mother–infant pairs with complete data on infant feeding during the first 6 months of life and sleep duration at 1 year. Infants were categorized as exclusively formula-fed for 6 months, breastfed for less than 6 months, breastfed for 6 months with formula supplementation, or exclusively breastfed for 6 months. The primary outcome was short sleep duration at 1 year, defined as fewer than 11 hours of sleep per day.
Short sleep duration was reported in about 12% of infants exclusively formula fed for 6 months compared with 10% of infants breastfed for less than 6 months, 10% of those breastfed for 6 months with formula supplementation, and 9% of those exclusively breastfed for 6 months. After adjustment for confounding factors, including maternal age, pregnancy complications, gestational age, infant sleep duration at 1 month, postpartum depression, daycare attendance, and socioeconomic characteristics, breastfeeding for less than 6 months was associated with 16% lower odds of short sleep, breastfeeding for 6 months with formula supplementation was associated with 21% lower odds, and exclusive breastfeeding for 6 months was associated with 23% lower odds compared with exclusive formula feeding.
The association was observed among infants who received breast milk alone and those who received both breast milk and formula during the first 6 months of life. The investigators suggested that differences in melatonin content, variation in tryptophan concentrations, and effects on the gut-brain axis may contribute to the observed association. However, these mechanisms were proposed as possible explanations and were not directly evaluated in the study.
The investigators acknowledged several limitations. Feeding practices and infant sleep duration were based on parental questionnaires and may have been subject to recall bias. Because the study was observational, the investigators could not establish a causal relationship. The overall effect size was modest, with a maximum absolute difference of about 3 percentage points between feeding groups, and residual confounding may have remained despite adjustment.
Overall, the findings suggested that breastfeeding during the first 6 months of life was associated with lower odds of short sleep at 1 year, although additional research is needed to determine whether the relationship is causal.
"Breastfeeding during the first 6 months of life was associated with a decreased risk of short sleep duration in 1-year-old infants," wrote lead study author Yuri Nakagawa, of the Department of Public Health in the Faculty of Medicine at the University of Toyama in Japan, and colleagues.
The study was funded by the Ministry of the Environment in Japan. The study authors reported no conflicts of interest.
