The best time of day to give your baby a vitamin D supplement is after breakfast and before lunch when oral dosing facilitates the absorption of calcium from food throughout the day. Vitamin D supplementation is usually given routinely in infancy, usually orally after breakfast and before lunch, i.e. in an empty stomach state, which allows the bioavailability of vitamin D to reach its highest level and optimal state. It is conducive to the growth and development of children and effectively prevents rickets. However, in summer, when the sunshine is sufficient and the baby’s outdoor activities reach more than two hours, you can stop taking vitamin D, and actively advocate breastfeeding and adding supplementary foods on time and reasonably. In addition, when the sun is directly on the baby’s skin, it can be directly converted into vitamin D. Therefore, more outdoor activities and sunshine are the best means to supplement vitamin D for babies.