REN and vitamin D deficiency: Second, low eGFR is associated with a host of “kidney specific” factors which include increased activity of renin-angiotensin system, neurohormonal activation, water and sodium retention, inflammation, vitamin D deficiency, calcium and phosphorus dysregulation, and increased asymmetric dimethyl arginine (ADMA) with greater bioavailability of nitric oxide, leading to endothelial dysfunction [24].