Vitamin D receptor activation may have pleiotropic effects in a variety of tissues. Experimental studies with vitamin D receptor activation demonstrate an ability to delay progression of renal disease. In humans, vitamin D receptor activation reduces albuminuria. Yet some clinical studies demonstrate that patients receiving vitamin D supplementation have an elevation in serum creatinine and a decline in estimated glomerular filtration rate. These observations may be explainable by an effect of vitamin D receptor activation on creatinine metabolism.