VITAMIN D 
Vitamin D (calciferol) is essential for proper skeletal formation and mineral homeostasis. Vitamin D deficiency in children causes deformation of the skeleton, resulting from the inadequate mineralization of bones. In industrially developed countries, milk and other foods are fortified with vitamin D, and hence rickets are very rare in these countries. When the skin is sufficiently exposed to sunlight, the amount of vitamin D synthesized can meet the requirements. The amount depends on area of skin exposed, time of exposure, and wavelength of ultraviolet light.
The allowance for children older than 6 months has been set at 10 mg (400 IU)/day (Table 5.6c). Because the complete maturation of the skeleton is not achieved until the third decade, this allowance is recommended through 24 years. There is a problem as to whether the usual sources of vitamin D are sufficient (milk, eggs, butter, etc.) without enough exposure to sunlight. However, in many industrialized countries, such as the United States, these foodstuffs are fortified by sufficient amounts of vitamin D.