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

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

Significance of Vitamin D Status in Obese Adolescents- A Pilot Study to Examine the Effect of Vitamin D3 Supplementation on Insulin Resistance and Cardiovascular Risk Factors

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: 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. Study the impact of vitamin D3 supplementation on various parameters reflecting insulin action, secretion, lipids and C-reactive protein in obese adolescents.

One arm would receive vitamin D3 at a dose of 400 IU by mouth once daily for 12 weeks and the other arm would receive vitamin D3 as a single oral daily dose of 2000 IU for 12 weeks.

Insulin resistance (IR) is a physiological condition in which cells fail to respond to the normal actions of the hormone insulin. The body produces insulin, but the cells in the body become resistant to insulin and are unable to use it as effectively, leading to hyperglycemia. Beta cells in the pancreas subsequently increase their production of insulin, further contributing to hyperinsulinemia. From the fasting glucose and insulin measurements, insulin resistance was calculated by the homeostasis model assessment of insulin resistance (HOMA -IR) as: HOMA -IR = fasting insulin concentration (µU/mL) x fasting glucose concentration (mmol/L)/22.5. High HOMA-IR scores denote increased insulin resistance.

LDL cholesterol is considered to be the main source of cholesterol buildup and blockage in the arteries. Less than 100 mg/dL is optimal, >130 mg/dL is borderline high, >160 mg/dL is high, >190 mg/dL is very high.

HDL (good) cholesterol protects against heart disease, so for HDL, higher numbers are better. A level less than 40 mg/dL is low and is considered a major risk factor because it increases your risk for developing heart disease. HDL levels of 60 mg/dL or more help to lower your risk for heart disease.

The current recommendation on fasting blood triglyceride levels: < 150 mg/dL is normal, >150 mg/dL is borderline high, and >200 mg/dL is high.

The high-sensitivity C-reactive protein test measures your risk for heart problems. <1.0 mg/L is lowest risk, 1.0-3.0 mg/L is average risk, and >3.0 mg/L is highest risk.

Inclusion Criteria: Age between 12-18 years BMI is at or greater than the 95th percentile for age and gender Exclusion Criteria: Subjects with 25 (OH)- D levels >100 ng/mL Serum calcium >10.8 mg/dL Current cancer Those taking a multivitamin supplementation Hepatic or renal disorders Type 1 or type 2 diabetes mellitus. 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

Javed A, Vella A, Balagopal PB, Fischer PR, Weaver AL, Piccinini F, Dalla Man C, Cobelli C, Giesler PD, Laugen JM, Kumar S. Cholecalciferol supplementation does not influence beta-cell function and insulin action in obese adolescents: a prospective double-blind randomized trial. J Nutr. 2015 Feb;145(2):284-90. doi: 10.3945/jn.114.202010. Epub 2014 Dec 17.