When to start calcium supplementation for newborns depends on individual factors and should be analyzed on a case-by-case basis, not as a generalization. Usually, newborns do not need additional calcium supplementation. If the mother’s calcium deficiency is obvious during pregnancy and the newborn has a soft scalp and obvious limb tremors, calcium supplementation is needed immediately after birth. If the newborn’s milk intake can reach 600ml or more, it can fully meet the calcium requirement without additional calcium supplementation. However, the absorption and utilization of calcium depends mainly on vitamin D. Therefore, newborns need to take vitamin D supplements at 2 weeks to stimulate the absorption of calcium. If calcium intake is too much, it may lead to constipation, premature closure of fontanelle, and even increase the excretion of calcium by the kidneys, causing kidney stones. Parents are advised to feed their children more calcium-containing foods after they add complementary foods to prevent calcium deficiency. If late teething, late toddler, occipital baldness, late closure of fontanelle, etc. occur, they need to take calcium supplements early.