Vitamin D in Renal Transplantation – from Biological Mechanisms to Clinical Benefits

Recent developments in our understanding of vitamin D show that it plays a significant role in immunological health, uniquely occupying both an anti‐microbial and immunoregulatory niche. Vitamin D deficiency is widespread amongst renal transplant recipients (RTRs), thus providing one patho‐mechanism that may influence the achievement of a successful degree of immunosuppression. It may also influence the development of the infectious, cardiovascular and neoplastic complications seen in RTRs. This review examines the biological roles of vitamin D in the immune system of relevance to renal transplantation (RTx) and evaluates whether vitamin D repletion may be relevant in determining immunologically‐related clinical outcomes in RTRs, (including graft survival, cardiovascular disease and cancer). While there are plausible biological and epidemiological reasons to undertake vitamin D repletion in RTRs, there are few randomized‐controlled trials in this area. Based on the available literature, we cannot at present categorically make the case for routine measurement and repletion of vitamin D in clinical practice but we do suggest that this is an area in urgent need of further randomized controlled level evidence. The authors examine the immunological functions of vitamin D relevant to transplantation and critically evaluate the available observational and interventional literature linking vitamin D to renal transplant outcomes.