婴幼儿身体处于生长发育的关键时期,尤其是骨骼的发育。正在生长的骨骼,如果不能进行正常的钙化作用,将导致骨骼病变。钙的吸收首先发生在十二指肠和空肠上段,这个过程依赖维生素D。人类维生素D的主要来源是人的皮肤产生的。阳光中的紫外线能促进皮肤中的7-脱氢胆固醇生成前维生素D_3,由淋巴等转运吸收入血, Infants and young children’s body is in a critical period of growth and development, especially bone development. The growing bones, if not normal calcification, will lead to skeletal lesions. Calcium absorption occurs first in the upper duodenum and jejunum, this process is dependent on vitamin D. The main source of human vitamin D is produced by human skin. Ultraviolet rays in the sun can promote the production of 7-dehydrocholesterol in the skin before the vitamin D_3, transported by the lymph and other transport into the blood,