Associations Between Breast Milk Energy Intake, Infant Sleep Duration and Time Until Next Feed

Background: Sleep in early infancy supports neurodevelopment, yet the influence of breast milk composition on sleep duration remains unclear. Objective: To determine whether breast milk energy intake is associated with the duration and timing of subsequent infant sleep episodes. Methods: Thirty-four healthy, fully breastfeeding mother–infant dyads (infant age: 3.7 ± 1.3 months) recorded 24-h infant feeding and sleep data, with feed volumes measured by pre- and post-feed test-weighing. Milk samples were collected and analysed for macronutrient concentrations to calculate energy intake per feed. Linear mixed-effects models were used to examine whether energy intake from the preceding feed was associated with subsequent sleep duration. Additional models evaluated lagged and cumulative energy intake, and mixed-effects modelling was used for associations between feed energy and time until the next feed. Results: Intake for 24-h infant breast milk was 851.8 ± 194.2 mL and sleep duration was 15.5 ± 3.4 h. The mean energy density of the feeds was 674.7 ± 140.7 kcal/L. Energy intake for the breastfeed preceding a sleep episode was not associated with sleep duration (β = 4.13 min; 95% CI −0.89 to 9.15; p = 0.106). Energy intake from lagged feeds and cumulative energy intake across the three preceding breastfeeds were also not associated with sleep duration (p = 0.171 and p = 0.290 respectively) nor the time until the next breastfeed (β = −0.025; 95% CI −6.2 to 1.4; p = 0.212). Conclusions: In healthy breastfed infants, the energetic content of breast milk feeds was not associated with subsequent sleep duration or the time until the next feed. These findings suggest that infant sleep–wake behaviour and feeding patterns were not associated with short-term variation in breast milk energy intake. Other factors, including circadian and developmental processes, are likely to contribute to infant sleep behaviour.