Vitamin D deficiency, a global health issue, may impact lactation by modulating mammary inflammation and lipid metabolism. In this study, we aimed to examine the impact of vitamin D supplementation on exclusive breastfeeding prevalence during early infancy. We found that the relative prevalence of non-exclusive breastfeeding was lower in early infancy among mothers receiving vitamin D supplements during pregnancy and lactation compared to placebo, but results were inconsistent across supplementation dosage groups.