The discovery that the vitamin D receptor is expressed in more than 30 tissues indicates that
the physiologic functions of vitamin D are much broader than its well-known role in the
regulation of calcium absorption and bone metabolism. There is evidence that vitamin D is
involved in the pathogenesis of cancer, cardiovascular disease, multiple sclerosis, and type
I diabetes. Recent epidemiological evidence points to a strong association between vitamin D
insufficiency and insulin resistance, the metabolic syndrome, and type II diabetes. The
investigators would like to examine the role of vitamin D in the development of insulin
resistance in overweight children and adolescents, which represent a high risk population for
cardiovascular and metabolic complications. The investigators propose a prospective
randomized clinical trial of vitamin D supplementation in overweight, insulin resistant,
vitamin D deficient children. The investigators objective is to assess if changes in insulin
resistance, fasting lipid profiles, blood pressure, and inflammatory markers occur in these
patients post treatment with vitamin D. Additionally, concomitant changes in calcium and bone
metabolism after vitamin D treatment will be evaluated. This is because, contrary to adults,
the optimal vitamin D concentrations that regulate calcium and bone metabolism have not been
established in pediatrics.