My goal for this career development award is to become an excellent independent investigator in patient-oriented research in chronic kidney disease progression. Chronic kidney disease (CKD) and end-stage renal disease (ESRD) are world-wide epidemics with an estimated 19 million people living with CKD and over 300,000 treated with dialysis in the United States. African-Americans and other minorities are disproportionately affected by ESRD with an incidence rate that is almost fourfold that of whites. Risk factors of initiation and progression of CKD and the factors underlying the racial disparities in ESRD have not been fully elucidated. Vitamin D has anti-proliferative and immunomodulatory properties and functions as an endocrine regulator of the renin-angiotensin system. As such, low levels of vitamin D are a potential novel risk factor for progression of CKD. In addition, African-Americans and Hispanics in the United States have lower vitamin D levels than whites, making differences in vitamin D a possible contributor to the differential CKD progression between African-Americans, Hispanics and whites. The first part of my research proposal will use data from the Women's Health Initiative to explore the factors underlying the differences in vitamin D levels between AA and whites. I will then use data from the NHANES III mortality and Medicare linkages to assess associations between low vitamin D levels and all-cause and cardiovascular-specific mortality and incident ESRD. If these associations exist, I will then evaluate whether differences in vitamin D levels may explain the racial disparities in ESRD. My third aim will be to conduct a randomized clinical trial of vitamin D repletion in a multi-ethnic population with CKD, vitamin D deficient and albuminuria to evaluate correction of vitamin D levels, and reductions in albuminuria and blood pressure. I have already proven my commitment and ability to become a successful clinical investigator by obtaining a Master's degree in Clinical Epidemiology and obtaining independent funding as a nephrology fellow through an individual NRSA. This K23 grant will allow me to develop my career through advanced formal coursework, intensive mentoring and the design, planning and conduct of a randomized clinical trial.