Vitamin D to Improve Endothelial Function in SLE

Determine the effect of vitamin D repletion on flow mediated dilation (FMD, a measure of endothelial function) in vitamin D deficient systemic lupus erythematosus (SLE) patients. The investigators will enroll vitamin D deficient SLE patients and randomize them to receive either 400 IU or 5,000 IU of cholecalciferol (D3) daily and measure change in FMD as a measure of EC function at baseline and after 16 weeks of repletion. Determine mechanisms by which vitamin D repletion may improve endothelial function in vitamin D deficient SLE patients and in vitro. Determine effect of oral D3 repletion on the Type I interferon signature in WISH and ECs cultured with pre and post plasma from D3 treated lupus patients. Determine effect of D3 repletion on the number of circulating apoptotic and non-apoptotic EC and EPC ex vivo. Determine effect of exogenous 1,25(OH)D on IFN gene signature in WISH and ECs stimulated by pretreatment SLE plasma in vitro. Determine the effects of exogenous 1,25(OH)D on the phenotype of ECs cultured with pretreatment lupus plasma. This study is designed to efficiently test our hypothesis and begin to define interferon-dependent pathways through which vitamin D repletion can restore clinical and in vitro endothelial function.