Cardiovascular Disease (CVD) and related disorders remain the leading cause of death in the nation. Hypovitaminosis D has been linked not only to several cardiovascular (CV) risk factors including hypertension, diabetes, obesity but also to increased rates of CVD. Thus,hypovitaminosis D presents a common pathway for a select subgroup with a clustering of CV risk factors in a profile that is predominant among ethnic minorities. Indeed, hypovitaminosis D is highly prevalent with an estimated 55% of the US adult population having levels at or below 30 ng/ml, and over 80% of African Americans having suboptimal values. Thus, we propose a twelve week randomized double-blind, placebo controlled pilot trial to assess the effect on vascular function and CV risk factors of 100,000 IU Vitamin D3 given every 4 weeks to overweight, hypertensive African-Americans with hypovitaminosis D. To our knowledge, the proposed project is the first to assess the effect of 'high-dose' Vitamin D3 administration on vascular function.We believe this study is also the first to examine the impact at a molecular level of Vitamin D3 repletion on the key mediators of cardio-metabolic pathways in humans. If our study results support our working hypothesis, we will be positioned to propose a larger scale study to detect a therapeutic effect on more definitive, clinical cardiovascular endpoints across a more diverse population.