Correction of Vitamin D Levels and Its Effect on Insulin Resistance and Weight Gain in Obese Youth

Vitamin D deficiency is extremely common in obese youth. In our obese population followed in the Endocrinology clinic at Children's Medical Center Dallas, vitamin D levels were inversely correlated with a measure of insulin resistance. We propose to show that correction of vitamin D levels in obese children and adolescents improves their insulin sensitivity. Obese youth presenting to the Center for Obesity and its Consequences on Health (COACH) clinic will be randomized to receive either the most recent Institute of Medicine (IOM) recommendations of minimum D3 dose of 600 IU/day (1), or receive higher doses of D3 such that the blood levels of vitamin D will be brought to a target level in either the low part or high part of the normal range. The goal is to determine if correction of vitamin D deficiency will improve insulin sensitivity in this group. Secondary goals include determining whether correction of vitamin D deficiency in obese adolescents and children results in less weight gain, and determining the amount of D3 required to correct vitamin D levels in this population. Our specific hypotheses are as follows: Hypothesis #1 Obese youth treated with Vitamin D3 who achieve low-normal 25-hydroxyvitamin D3 (OHD) levels (30-50 ng/mL) or high-normal 25-OHD levels (60-80 ng/mL) will have improved insulin resistance, as measured by Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), compared to those individuals with deficient 25-OHD levels (\< 30 ng/mL). Hypothesis #2 Subjects with a higher BMI will have higher Vitamin D dose requirements than current IOM recommendations of 600 IU/day and will take a longer period of time to reach target 25-OHD levels. Hypothesis #3 Subjects with normal 25-OHD levels will demonstrate less weight gain compared to subjects on the control arm.