Impact of Vitamin D on Diabetic Kidney Disease in African Americans

• Progression of Kidney Disease [ Time Frame: 6 months ] [ Designated as safety issue: No ]
  Urinary Albumin:Creatinine Ratio (ACR) is a well-established, sensitive marker of nephropathy progression. We will calculate an average urine albumin (mg/dL) to urine creatinine (g/dL) ratio based on three first-morning spot collections. ACR will be measured by a turbidimetric method using SYNCHRON® System every 6 months. An increase in a subject's mean ACR will be considered an indicator of disease progression.
  
  

• Decrease in Estimated Glomerular Filtration Rate (eGFR) [ Time Frame: 6 months ] [ Designated as safety issue: No ]
  Estimated Glomerular Filtration Rate (eGFR) will be evaluated every 6 months, since changes in eGFR and ACR may occur independently and represent different pathways to the development of renal insufficiency. eGFR will be calculated via the Modification of Diet in Renal Disease (MDRD) equation of 4 variables (Cr level, age, sex, race) per NKF recommendations, with serum creatinine (Cr) measured using the SYNCHRON® System by means of the Jaffe rate method. For the purposes of this study, a decrease in eGFR will serve as a secondary outcome measure.
  
  

Diabetic kidney disease is increasing in prevalence and is associated with significant morbidity and mortality. Health disparities exist in the progression of diabetic kidney disease, with minorities being more affected even when adjusting for treatment, glycemic and hypertensive control, and medical coverage. Secondary prevention of the progression of diabetic kidney disease is hindered by a lack of easily modifiable risk factors. Based on animal and observational human studies, vitamin D deficiency is potentially a novel, modifiable risk factor that may interrupt or delay the progression of diabetic kidney disease through direct effects as well as by helping to ameliorate kidney disease risk factors, such as hyperglycemia, hypertension and inflammation. In addition, based on minorities having a higher prevalence of vitamin D deficiency, it may also potentially impact the differential progression of diabetic kidney disease in minorities. However, clinical trials evaluating the impact of vitamin D supplementation on diabetic kidney disease are lacking. Thus, this pilot study funded as an R03 through the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) has the following specific aims: (1): To evaluate the impact of vitamin D supplementation (vitamin D3 at 400 IU/d versus 4000 IU/d) on the proportion of individuals with progression of albuminuria over 12 months in a sample of African American participants with vitamin D deficiency in a randomized controlled trial. (2): To identify whether kidney disease risk factors such as blood pressure and glycemic control mediate the impact of vitamin D supplementation on the progression of albuminuria over 12 months in a sample of African American participants with vitamin D deficiency in a randomized controlled trial.