The investigators' project will study the effects of optimizing the vit D status of obese adolescents on markers of glucose metabolism and inflammation.

The alarming rise in pediatric obesity over the past few decades has been associated with an increase in the occurrence of impaired glucose tolerance and inflammation in children and adolescents. These conditions are part of the "metabolic syndrome", and children with risk factors such as these are much more likely to develop cardiovascular disease or diabetes as adults compared with their lean peers. Within the last few years there has been a growing body of evidence that optimizing vitamin D (vit D) status may alleviate these obesity-associated complications. Further, there is also research that shows that the better the vit D status of overweight individuals, the more favorably they respond to dieting by losing more body fat. The prevalence of vit D deficiency/insufficiency in the North American population has been classified as an "epidemic" by experts in the field and obese teens are considered at an even greater risk for deficiency because they tend to store vit D in their fat stores which is not readily mobilized for use by the body. The investigators' project will study the effects of optimizing the vit D status of obese adolescents on markers of glucose metabolism and inflammation. Obese teens attending an established adolescent weight loss clinic will be supplemented with high-dose vit D for 6 months (mos) which will be administered concurrently with their standard medical care and treatment. At baseline, 3 mos and 6 mos the investigators will measure vit D status, serum markers of insulin sensitivity and glucose metabolism; serum markers of inflammation; and body weight/height and waist circumference. At baseline and 6 mos only the investigators also measure body composition (percent body fat by dual-energy x-ray absorptiometry) and confounding lifestyle factors known to affect vit D, glucose metabolism or inflammation (e.g., nutrient intake, physical activity, sun exposure, pubertal stage). Results gleaned from this study will help to advance the prevention and treatment of obesity-related complications and have the potential to lead to significant reductions in healthcare costs and co-morbidities.

Inclusion Criteria:

• Obese adolescent (BMI > 85th percentile for age)
• 9-19 years of age
• attending the ADOBE clinic at the University of Missouri

Exclusion Criteria:

• use of vit D supplements other than standard multi-vitamin preparation
• (i.e., should not be receiving vit D > 1000 IU/d) use of medications that interfere with vit D metabolism (e.g., anti-convulsive)
• history of hepatic or renal disorders;
• undergoing ultraviolet radiation as medical therapy;
• pregnancy;
• cigarette smoking;
• current use of commercial tanning bed;