Whether a baby is deficient in calcium has always been a matter of great concern to parents. Parents are justified in worrying about whether their babies are deficient in calcium because physical growth and development are rapid in infancy. They are around 50 centimeters long at one month, 25 centimeters long on average at one year old, and 10 and 8 centimeters long in the second and third years, respectively. With such rapid growth, their bones need a lot of calcium and phosphorus to harden. So, how can you tell if your baby has a calcium deficiency? Does your baby have a calcium deficiency? If there is a calcium deficiency, babies can have softening of the skull, which is manifested by a ping-pong feeling when the skull is pressed. Standing and weight bearing will cause the lower limbs to change shape, forming “O” shaped legs or “X” legs. Early manifestations include excessive sweating at night, occipital baldness, restless sleep and easy to startle. Can calcium deficiency be solved by supplementing calcium? In fact, simply supplementing calcium cannot solve the problem, but must first be supplemented with vitamin D. Vitamin D promotes the absorption of calcium and phosphorus from the small intestine, so that calcium can be deposited from the blood into the fast-growing bones, making the bones hard. The main source of calcium is dairy products, milk is a natural calcium supplement. If you can consume 600 milliliters of milk per day, either formula or mother’s milk, the amount of calcium in milk is sufficient. However, if there is a lack of vitamin D, the calcium in milk is not easily absorbed and utilized. Therefore, lack of vitamin D is the “cause” and lack of calcium is the “effect”. If the amount of milk is sufficient, vitamin D should be supplemented first. Only if the amount of milk is insufficient or the baby grows too fast, calcium should be supplemented at the same time. Where does vitamin D come from in infants? Oral vitamin D. Except for the liver of marine fish which contains some amount of vitamin D in food, the content in dairy (including human milk and cow’s milk), egg yolk and meat is very small, and there is almost no vitamin D in grains, vegetables and fruits. The vitamin D that infants and young children take in from natural food every day cannot meet the needs of their development. Normal babies, regardless of age, need 400 units of vitamin D supplementation per person per day, while preterm babies, those with congenital storage deficiencies, or overgrown infants need increased amounts. Therefore, the amount of oral vitamin D should be increased appropriately. Vitamin D taking, generally from half a month after birth, can be served until 3 years old. Appropriate sun exposure, often let the baby in the outdoor activities. Spring and fall days, but also directly let the baby in the sun, summer in the shade, so that the baby’s skin is often exposed to ultraviolet rays. Ultraviolet irradiation can promote the 7-dehydrocholesterol stored in the skin, photochemically converted into vitamin D3.