In the clinic, I often meet parents who ask for trace elements to see if their children are deficient in calcium, and whenever I encounter this situation, I will give some explanation. When the concentration of calcium ions in the blood decreases, the absorption of calcium from food in the small intestine will increase, and calcium will be released from the bones to replenish the missing calcium ions in the blood. When the bones are deficient in calcium, it does not necessarily mean that the blood calcium will be low. What people usually call calcium deficiency is caused by vitamin D deficiency. The function of vitamin D is to increase the absorption of calcium in the intestine and promote the transfer of calcium to the bones. Vitamin D deficiency not only causes night terrors, sweating, square cranium and other symptoms of rickets in small infants, but also weakens the child’s resistance and makes the child susceptible to infectious and immune diseases. Growing pains in children during the rapid growth period are also often associated with vitamin D deficiency. In adults, especially menopausal women, vitamin D deficiency significantly increases the incidence of fractures, and they need more vitamin D than normal to resist hormone-induced bone calcium loss and maintain bone stability. The American Academy of Pediatrics recommends that children take 400 IU of vitamin D daily from birth to age 2, and I personally support this recommendation until adulthood. I personally suggest that children and adolescents should be supplemented with vitamin D and calcium. The current market is full of D and calcium supplement products, who can not try one by one, how to choose? It depends on the results. It is important to check in time and never delay the child.