The purpose of this research study is to determine whether taking vitamin D, every day, over a 12 week period will improve the vitamin D status, risks for poor heart health, risks for developing type 2 diabetes, and/or muscle strength in overweight, African American teenagers with low vitamin D levels.

Vitamin D deficiency/insufficiency is common throughout the lifespan, and across all race and ethnic groups. The American Academy of Pediatrics (AAP) recently recommended supplementation dose to 400 international units (IU) daily in all children. These recommendations target rickets prevention, but address neither the vitamin D supplementation necessary to optimize bone health nor the nontraditional vitamin D roles in immune disease, insulin resistance, muscle function, and cardiovascular disease (CVD). Moreover, the AAP recommendation noted that it had little pediatric data upon which to base guidelines. The Institute of Medicine also recently published Dietary Reference Intakes for Calcium and Vitamin D: the estimated average requirement in children and adults was set at 400(IU) daily and the recommend dietary allowance was set at 600 IU daily. Data on outcomes and supplementation levels in African Americans (a population at particular risk for vitamin D deficiency) and across pediatric age ranges and body habitus types, are lacking. The Vitamin D supplementation requirement in obese, African American adolescents is particularly problematic since obesity is associated with 1) lower circulating vitamin D levels (25OHD) and 2) insulin resistance. This pilot study will examine the effect of vitamin D supplementation upon 25OHD, the serum marker of vitamin D status, in obese, African American adolescents with vitamin D deficiency. Subjects will be randomized to receive cholecalciferol 1000 IU or 5000 IU daily for 3 months. Serum 25OHD, parathyroid hormone, glucose, insulin, CVD risk markers, and measures of muscle function and pain will be obtained at baseline and post-treatment. This pilot study will provide data on serum 25OHD responses to vitamin D at doses more likely to meaningfully impact 25OHD than the current American Academy of Pediatrics (AAP) supplementation guideline. Responses to supplementation can then inform future clinical trials aimed at addressing outcomes of vitamin D replacement on insulin sensitivity and CVD risk in obese adolescents.

Inclusion Criteria:

• African American
• Obese [body mass index (BMI) greater than or equal to 95th percentile for age and sex]
• Pubertal (Tanner Stage greater than 1)
• 25OHD less than 20 ng/mL (for treatment phase); if 25OHD is greater than or equal to 20 ng/mL, only baseline data will be obtained.
• Committed to adherence to supplementation and study completion

Exclusion Criteria:

• Pregnancy
• Chronic medical conditions or medications use that can affect growth, nutrition, bone health, vitamin D metabolism, glucose, or insulin sensitivity
• Known history of hypercalcemia or hypercalciuria
• Non-English speaking, as assessments are available only in English