Out of the misunderstanding: after the baby is born, supplementation of vitamin D is necessary, and normal-born children need to supplement vitamin D 400 international units / day, generally from half a month after birth, until 2-3 years old. Premature babies should be supplemented with vitamin D 800 international units/day-1000 international units/day immediately after birth, and corrected to 400 international units/day after 3 months of age until 2-3 years old. Infants and children grow fast and the rapid growth of bones requires more calcium to be deposited in the bone. Vitamin D promotes the absorption of calcium and phosphorus from the small intestine, so that calcium is deposited from the blood into the fast-growing bones and makes the bones hard. Therefore, calcium deficiency in infants and children is mostly caused by insufficient vitamin D. Calcium deficiency is the “fruit”, while vitamin D deficiency is the “cause” of calcium deficiency. Where does vitamin D come from? Proper sunlight: This is the most effective, convenient and economical way. Parents can increase their baby’s outdoor activities. In spring and autumn, you can let your baby directly under the sun, while in summer, you should be in the shade. UV exposure promotes the photochemical conversion of 7-dehydrocholesterol stored in the skin to vitamin D3. Sunlight exposure allows the skin to store vitamin D3 as a backup and does not cause vitamin D overload. Oral vitamin D: Except for the liver of sea fish, which contains some amount of vitamin D, food contains very little in dairy (both human and cow’s milk), egg yolk and meat, and almost none in cereals, vegetables and fruits. The daily intake of vitamin D from natural foods does not meet the developmental needs of infants and children, so they need to take oral vitamin D supplements. What do I need to know about taking vitamin D? In addition to vitamin D preparations, formula milk also contains a certain amount of vitamin D. Formula-fed babies need to be supplemented according to the amount of vitamin D contained in formula milk. It is not advisable for breastfeeding mothers to supplement with vitamin D. Even if the mother supplements with 2,000 international units of vitamin D per day, the amount of vitamin D that can be given to the baby through breast milk is very little, and if the amount of supplementation is too much, reaching 4,000 international units, it can cause poisoning to the mother. Reminder: 400 international units of vitamin D for babies is a daily preventive dose, not a therapeutic dose. If the baby has rickets, the dose must be increased under the guidance of the doctor and given the appropriate treatment. Some parents stop taking vitamin D when their child is sick, which is not right. In addition to preventing rickets, vitamin D can also improve resistance and facilitate recovery from illness, so it should continue to be taken when you are sick.