Normalization of Vitamin D Levels and its Effect on Insulin Resistance in Obese Youth
The proposed study is a prospective, unblinded dose-ranging trial to examine in obese youth 1) the effect of correcting Vitamin D deficiency on insulin resistance, 2) the effect of correcting Vit D deficiency on weight gain, and 3) the amount of Vit D3 required to achieve Vit D sufficiency in obese adolescents. Subjects will be recruited from obese children and adolescents aged 6 to 17 years presenting to the COACH clinic, a referral clinic for obese children at Children[Right Quote]s Medical Center of Dallas. Approximately 1300 new patients are seen in the COACH clinic each year. Ethnicity will be self-assigned as African-American, Caucasian, Hispanic, or Other. The ethnic makeup of the COACH clinic over the last 20 months was as follows: African-American 25%, Caucasian 19.5%, Hispanic 52%, and Other 3.5%.
As per standard practice in the COACH clinic, a height (cm), weight (kg), and blood pressure will be obtained, and body mass index (kg/m2) calculated for each patient. Fasting total cholesterol, LDL, HDL, triglyceride, 25-OHD, Hemoglobin A1c (A1c), and fasting insulin will be obtained, and an Oral Glucose Tolerance Test (OGTT) performed. The baseline estimate of insulin sensitivity is calculated from the fasting insulin and glucose values, and reported as the HOMA-IR. After Informed Consent has been obtained, participants will be randomized to either the Control group (600 IU/day OR 5000 IU/wk), the Low-normal 25-OHD group (target 25-OHD 30-50 ng/mL), or the High-normal 25-OHD group (target 25-OHD 60-80 ng/mL). A 25-OHD and amp;gt; 25 ng/mL will be confirmed. These groups will be matched for age (6-12 years versus 13-17 years) and ethnicity (Caucasian versus African-American verus Hispanic). Approximately 60 patients will be recruited for each group. Subject participation will continue until Vit D sufficiency has been documented for 4 consecutive months, at which point the fasting insulin and glucose values will be repeated for calculation of HOMA-IR and assessment of insulin sensitivity, and amount of weight gain will be measured.
The criteria for referral to the COACH clinic are 1) age 6-17 years old, and 2) weight > 90th percentile. Inclusion criteria include children aged 6-17 years presenting to their first COACH clinic visit who meet the criteria for obesity (BMI > 95th percentile for age) and have a 25-OHD < 25 ng/mL. All ethnicities, both genders, and both English and Spanish speaking subjects are eligible to be included in the study.