Vitamin D in the Patients with Chronic Kidney Disease: When, to Whom and in Which Form

Alteration in vitamin D metabolism has a central role in the pathogenesis of secondary hyperparathyroidism (SHPT) and is also associated with increased cardiovascular morbidity and mortality in patients with chronic kidney disease (CKD). For more than sixty years, vitamin D, nutritional vitamin D (ergocalciferol, cholecalciferol or calcifediol) and nonselective vitamin D receptor (VDR) activators (calcitriol, alfacalcidol) have been used in the prevention and treatment of SHPT. In the last twenty years, selective VDR activators (paricalcitol, maxacalcitol) have been used to target SHPT. However, there are many open questions regarding use of nutritional vitamin D or VDR activators. The K/DOQI and KDIGO guidelines recommended testing for vitamin D insufficiency and deficiency in patients with CKD, but there is no consensus on the definition of vitamin D insufficiency in CKD. There are a many open questions, for example, regarding the optimal nutritional vitamin D type and the dose and co-administration of nutritional vitamin and VDR activators. Therapy with VDRAs is required in the majority of patients with CKD, particularly in dialysis patients. However, when to start with VDRAs is not so apparent. Is PTH level the only indication of when to start therapy? Although VDRAs are very effective in lowering PTH levels and bone metabolism the effect of patients mortality is not so straightforward. Despite many unanswered questions, there is a large body of experimental and clinical data to support vitamin D use in patients with CKD. To obtain answers to the open questions, we need more randomized controlled trials.