The American Academy of Pediatrics (AAP) has doubled the recommended intake of vitamin D to 400 IU per day for infants, children, and adolescents.

Because levels of sunlight exposure adequate for the cutaneous synthesis of vitamin D may increase the risk of skin cancer, and because natural dietary sources of vitamin D are limited, the new recommendations include all infants, including those who are exclusively breastfed, and older children and adolescents.

Historically, the main source of vitamin D has been via synthesis from cholesterol after exposure to ultraviolet B (UVB) light. Full-body exposure for 10 to 15 minutes during the summer will generate 10,000 to 20,000 IU of vitamin D₃ in adults with light skin pigmentation; persons with darker skin pigmentation require five to 10 times more exposure to generate similar amounts. However, many other factors affect the amount of UVB exposure beyond time spent outdoors: the amount of skin pigmentation, body mass, degree of latitude, season, cloud cover, air pollution, amount of skin exposed, and UVB protection (e.g., clothing, sunscreen). Although the AAP encourages physical activity and time spent outdoors, children's activities that minimize sunlight exposure are preferred. However, in following these guidelines, infants, children, and adolescents require vitamin D supplementation.

Vitamin D Deficiency

New cases of rickets, a preventable condition caused by inadequate vitamin D intake and decreased exposure to sunlight, continue to be reported in the United States. Rickets is characterized by enlargement of the skull, joints of the long bones, and rib cage; curvature of the spine and femurs; and generalized muscle weakness. It is an example of extreme vitamin D deficiency, but deficiency typically occurs months before rickets is obvious on physical examination.

Children with vitamin D deficiency may present with hypocalcemic seizures, growth failure, lethargy, irritability, and a predisposition to respiratory infections during infancy. Clinical effects of vitamin D deficiency include decreased dietary calcium absorption, decreased levels of serum 25-hydroxyvitamin D, and increased levels of parathyroid hormone (in older infants, children, and adolescents). The increase in parathyroid hormone levels causes calcium loss from bones, leading to reduced bone mass and increased risk of fractures.

Serum 25-hydroxyvitamin D concentrations should be at least 20 ng per mL (50 nmol per L) in infants and children. Based on the most current evidence, vitamin D deficiency in adults is defined as a 25-hydroxyvitamin D concentration of less than 50 nmol per L; vitamin D insufficiency is defined as a concentration of 20 to 32 ng per mL (50 to 80 nmol per L). There is no consensus for these definitions in infants and children, but it has been proven that 200 IU of vitamin D per day will not maintain 25-hydroxyvitamin D concentrations above 50 nmol per L in infants.

Vitamin D Supplementation

Infants who are exclusively or partially breastfed should receive 400 IU of supplemental vitamin D daily, beginning in the first few days of life. Supplementation should continue until the infant is weaned to at least 1 qt (1 L) of vitamin D–fortified formula or whole milk per day. Infants who are not breastfed, as well as older children who drink less than 1 qt of vitamin D–fortified milk per day, should also receive 400 IU of supplemental vitamin D per day. Other dietary sources of vitamin D (e.g., fatty fish, fortified cereal, egg yolks) may be included in the daily intake. Adolescents who do not obtain 400 IU of vitamin D per day through fortified milk or foods should also receive supplemental vitamin D.

Vitamin D intake of 400 IU per day may be inadequate to prevent deficiency in children at increased risk, such as those with chronic fat malabsorption and those taking long-term antiseizure medications. Higher dosages of vitamin D supplements may be needed in these children, and vitamin D status should be monitored by laboratory tests (e.g., measurement of 25-hydroxyvitamin D, parathyroid hormone, and bone mineral levels).