Effect of Vitamin D3 Supplementation on Insulin Resistance and Cardiovascular Risk Factors in Obese Adolescents

The prevalence of obesity has reached epidemic proportions nationally as well as internationally. Currently, 16 % of American adolescents are obese. In adults, obesity is a risk factor for vitamin D insufficiency and up to 80% of obese adults have been noted to vitamin D insufficient. In adults, low vitamin D status appears to be associated with the development of type 2 diabetes and metabolic syndrome. There is little information on the prevalence of vitamin D insufficiency and its implications in obese adolescents. Additionally, it is unknown whether treatment of vitamin D insufficiency in adolescents might result in improvement in insulin resistance, lipids and cardiovascular risk markers.

We hypothesize that vitamin D insufficiency correlates positively with insulin resistance and cardiovascular risk in obese adolescents and that vitamin D3 supplementation improves insulin resistance and cardiovascular risk factors in this population. The purpose of the study is to determine the impact of vitamin D3 supplementation on various parameters of insulin secretion, insulin action, lipids and C-reactive protein in obese adolescents.

The problem of childhood obesity has reached epidemic proportions both nationally and internationally. The prevalence of obesity has tripled in the last three decades and currently 16 % of American adolescents are obese. Nearly 30% of obese adolescents demonstrate a metabolic syndrome characterized by insulin resistance and dyslipidemia. These abnormalities lead to the development of type 2 diabetes mellitus and to increased cardiovascular morbidity and mortality. Obesity is a well-known risk factor for vitamin D insufficiency and up to 80% of obese adults have been found to be insufficient in vitamin D. Observational studies in adults have shown consistent associations between low vitamin D status and prevalence of type 2 diabetes mellitus and metabolic syndrome. There is paucity of data on the prevalence of vitamin D insufficiency and its implications in obese adolescents. It is also not known whether treatment of vitamin D insufficiency in children or adults might result in improvement in insulin resistance and cardiovascular risk factors.

Hypotheses: We hypothesize that vitamin D insufficiency correlates positively with insulin resistance and cardiovascular risk in obese adolescents and that vitamin D3 supplementation decreases insulin resistance and cardiovascular risk factors in this population.

Objectives:

1. Determine if there is any correlation between serum 25(OH)D levels and homeostasis model assessment of insulin resistance (HOMA-IR), HDL cholesterol and C-reactive protein, in obese adolescents.
2. Study the impact of vitamin D3 supplementation on various parameters reflecting insulin action, secretion, lipids and C-reactive protein in obese adolescents.

Eligibility Criteria:
Inclusion Criteria:

1. Age between 12-18 years
2. BMI is at or greater than the 95th percentile for age and gender

Exclusion Criteria:

1. Subjects with 25 (OH)- D levels \>100 ng/mL
2. Serum calcium \>10.8 mg/dL
3. Current cancer
4. Those taking a multivitamin supplementation
5. Hepatic or renal disorders
6. Type 1 or type 2 diabetes mellitus.
7. Those receiving insulin, metformin or oral hypoglycemic medications

   * Use of glucocorticoids and anti-seizure medications in the previous 6 months
   * Malabsorption syndromes such as celiac disease