**6. Conclusion**

Vitamin D metabolism is significantly impaired at different levels in the early stages of renal disease. The influence of the abnormalities spans beyond calcium-phosphorus metabolism, having impact on mortality, cardiovascular morbidity, cancer risk, renal protection, etc. Thus, VD metabolites have pivotal role in controlling a great number of intracellular pathways that are impaired in renal disease contributing to poorer patient outcomes. However, there are still problems to be clarified: the dose of vitamin D supplementation, target levels of 25-hydroxyvitamin D and PTH in predialysis patients, possible biochemical abnormalities due to treatment (hypercalcemia, hyperphosphatemia), and vitamin D pleiotropy in CKD patients prior and after kidney transplantation. The great number of unsettled problems in this sphere and its great potential for improving patient outcomes guarantee that vitamin D will be a "hot topic" in the world of renal disease over the next years.
