Feeding Mode Is Associated with Infant Night Sleep Trajectories During the First Postnatal Year

Background: Short sleep and formula feeding during infancy are associated with increased risk of childhood obesity. Feeding practices and sleep arrangements vary during infancy and may also be dynamic, yet their impact on infant night sleep duration remains unclear. Understanding these relationships is crucial for formulating recommendations to support breastfeeding and address sleep concerns. Objective: We examined the association between feeding mode and parent-reported infant night sleep duration during the first postnatal year, while additionally evaluating night-weaning and bedsharing as contextual sleep-related practices. Methods: Infants in the Phoenix Metropolitan Area (n = 193) were followed up at 3, 8, 13, 26, 39, and 52 weeks post-birth. Sleep and feeding questionnaires were answered at each visit. A multilevel growth model estimated infant night sleep duration trajectories by feeding mode (ordinal: exclusive formula, mixed, exclusive breastfeeding), night-weaning, and bedsharing as time-variant predictors. Maternal education and household income were covariates to account for differences in study attrition. Results: Infant night sleep duration followed a curvilinear trajectory, starting at 7.92 h (95% CI: 5.78, 10.06) and increasing by 0.40 h/month (95% CI: 0.21, 0.60), with a deceleration over time (0.02 h/month², p < 0.001). Each increase in levels of breast milk consumption was associated with an increase in infant night sleep duration (B = 0.87 h, p < 0.001), but the association weakened as the infant aged (B = -0.07 h/month, p < 0.001). Despite 59.7% of bedsharing infants being exclusively breastfed, bedsharing was not significantly associated with infant night sleep duration. Similarly, night-weaning was not significantly associated with infant night sleep duration. Conclusions: Breastfeeding is associated with longer infant night sleep duration, whereas bedsharing showed no association despite its correlation with breastfeeding. This research highlights the importance of breastfeeding in early life, not only for its developmental benefits but also for its relationship with infant night sleep duration, an essential component of healthy infant growth.