Renoprotective effects of Vitamin D and renin-angiotensin system.

Vitamin D has many physiological functions. First it is a primary regulator of calcium homeostasis. Beyond that, vitamin D and its receptors (VDR) play important role in the immune system, cardiovascular system, reproductive system and insulin resistance. An important aspect of vitamin D pleiotropic effects is the interaction with components of the renin-angiotensin system (RAS). It was demonstrated that vitamin D-null mice have a sustained elevation of renin expression. The combination of both the AT1 blockers and the vitamin D analogues, leads to a marked amelioration of the molecular and clinical markers of diabetic nephropathy. This combination may protect the kidney through the effects on both the glomerular and the tubulointerstitial compartments. There are different studies that corroborate the renoprotective action of vitamin D in CKD. In fact the renoprotective mechanisms in humans remain to be assessed, but these are realized through reduction of proteinuria, high blood pressure, inflammation as well as hemodynamic effects. An important mechanism is the role of vitamin D as a potent negative endocrine regulator of renin expression. It was shown that low levels of vitamin D represent a novel risk factor for the progression of renal disease but it is not demonstrated yet that vitamin D can prolong the time to end-stage renal disease. This question remains to be answered in other future controlled clinical trials.