The Effects of Vitamin D on Glycemic Control and Proinflammatory Markers in Adolescents With T1DM

Inclusion Criteria: 1. Between 13 to 21 years of age, with at least Tanner stage 4 sexual maturity for males or post-menarchal females, and T1DM for at least 1 year. To ensure that inclusion criteria for sexual maturity are met, a physical exam for research purposes will be performed. 2. HbA1c between 7 to 9% 3. Adequate renal function (serum creatinine \< 1.5 mg/dL in males and \< 1.2 mg/dL in females) and adequate liver function (AST and ALT \< 2.5 times the upper limit of normal) 4. Vitamin D insufficiency or deficiency (25-OH vit D level \< 30ng/mL) which will be determined on initial screening labs after consenting subjects. Exclusion Criteria: 1. Less than 13 or greater than 21 years of age 2. Less than Tanner stage 4 sexual maturity for males or pre-menarche 3. HbA1c less than 7% or greater than 9% 4. T1DM for less than 1 year 5. Vitamin D sufficient (25-OH vit D level \> 30 ng/mL) 6. Currently taking any medication that can interfere with vitamin D synthesis or metabolism, including but not limited to Orlistat, Phenobarbital, Dilantin, Anti-tuberculosis drugs 7. Currently taking any medication other than insulin that alters blood glucose levels, including but not limited to systemic glucocorticoids 8. Inadequate renal function (serum creatinine \> 1.5mg/dL in males and \> 1.2mg/dL in females) or inadequate liver function (AST and ALT \> 2.5 times the upper limit of normal) 9. Evidence of malabsorption or short gut.