While there is still much we need to learn about the role of vitamin D in health and disease, we do know that many children and adolescents in the U.S. have suboptimal levels.
A U.S. study of 559 adolescents (mean age, 16 years; 45% black) showed that 29% had deficient serum 25-hydroxyvitamin D (25[OH]D) levels (deficiency, <20 src="http://www.jwatch.org/math/le.gif" alt="≤" border="0">10 ng/mL); regardless of season, black adolescents were significantly more likely than whites to have deficient levels, with severe deficiency in 11% of blacks versus 0% of whites (JW Pediatr Adolesc Med Jun 16 2010). Data from the National Health and Nutrition Examination Survey (NHANES) suggest that nearly 51 million children and adolescents have insufficient vitamin D levels (15–29 ng/mL) and 7.6 million have deficient levels (<15 href="http://pediatrics.jwatch.org/cgi/content/full/2009/1104/1">JW Pediatr Adolesc Med Nov 4 2009).
Vitamin D levels have been reported to be inversely associated with several diseases or adverse physiologic attributes. In a recently published longitudinal study, suboptimal vitamin D levels were associated with greater increases in body-mass index (BMI), waist circumference, and subscapular-to-triceps skinfold-thickness ratio over time, compared with sufficient vitamin D levels (JW Pediatr Adolesc Med Dec 8 2010). In a study of 92 black children with physician-verified asthma, 54% had serum 25(OH)D levels <20 href="http://pediatrics.jwatch.org/cgi/content/full/2010/616/5">JW Pediatr Adolesc Med Jun 16 2010). Low vitamin D levels have also been correlated with higher parathyroid hormone levels and systolic blood pressure and with lower levels of calcium and HDL cholesterol. Children with the lowest vitamin D levels (<15 href="http://pediatrics.jwatch.org/cgi/content/full/2009/1104/1">JW Pediatr Adolesc Med Nov 4 2009).
Apparently, most of us cannot "tan" our way out of this problem, at least not during seasons other than summer. After 2 PM in Boston during the winter, not even individuals with the fairest of skin (Fitzpatrick type I) could spend enough time in the sun to synthesize adequate vitamin D. In Miami, people with type V skin (brown skin that rarely burns) would need 15 minutes of sun exposure at noon in the summer and 29 minutes of sun exposure at noon in the winter to make 1000 IU of vitamin D (JW Dermatol Jun 4 2010).
Although consumption of milk at least once per week and vitamin D supplements reduce the risk for vitamin D deficiency (JW Pediatr Adolesc Med Nov 4 2009), precious few data show that vitamin D supplementation can ameliorate or prevent any of the disease states described above. In a randomized controlled trial of vitamin D supplementation (400 IU) in 164 healthy Finnish army conscripts, the supplemented group was no less likely to develop respiratory infections, report cold or flu symptoms, or miss days of work than the placebo group, even though vitamin D levels fell 30% in the control group and remained stable in the supplemented group (JW Gen Med Sep 14 2010).
This lack of data on the relation between health outcomes other than bone health and vitamin D status is reflected in a newly released Institute of Medicine (IOM) report on dietary reference intakes for calcium and vitamin D (JW Dermatology 2010 Dec 17). The IOM concluded that bone health is the only health outcome that satisfies criteria for use as an "indicator" in developing recommended dietary intakes. Insufficient data (specifically, those from randomized controlled trials) exist to support dose-response relations between vitamin D levels and other health outcomes. On the basis of the existing evidence regarding vitamin D and bone health, the IOM established 600 IU as the recommended daily allowance (RDA) for all infants, children, and adolescents (age range, 1–19 years) and e stimated that this level would result in a 25(OH)D concentration 
20 ng/mL in at least 97.5% of children. This RDA is 50% higher than the intake of 400 IU currently recommended by the American Academy of Pediatrics. The report also reiterated that children and adolescents, especially girls, should consume at least 1300 mg of calcium per day. Additional commentary on the IOM recommendations is available here.
— Alain Joffe, MD, MPH, FAAP
Published in Journal Watch Pediatrics and Adolescent Medicine January 5, 2011
