The main role of vitamin D supplementation in newborns is to prevent vitamin D deficiency rickets, because vitamin D is a fat-soluble vitamin that can promote the absorption of calcium in the intestine, as the calcium content of milk or other soy products is very high. But even higher calcium in the intestine cannot be effectively used and absorbed by the body without the participation of vitamin D. If the calcium is not absorbed effectively, it can cause a drop in the calcium level in the child’s blood, which can lead to hypocalcemia. After the child has hypocalcemia, it will cause vitamin D deficiency rickets, and the child will have occipital baldness, very excessive sweating, rib beading, and chicken chest. Therefore, newborns should be routinely supplemented with vitamin D two weeks after birth to effectively prevent the occurrence of vitamin D deficiency rickets.