Context: Bone disease after kidney transplantation is a common problem. The serum levels of the active vitamin D metabolite 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D] have been extensively studied. In contrast, there has not been much concern about the serum levels of 25-hydroxyvitamin D₃ [25(OH)D]. However, it is well recognized that serum levels of 1,25(OH)₂D are often normal in vitamin D deficient patients. Moreover, inadequate serum 25(OH)D may limit the extrarenal production of 1,25(OH)₂D that could lead to increased risk of many chronic diseases.

Objective: We analyzed whether renal transplant patients were at a higher risk of 25(OH)D deficiency, due to the consequence of their need to protect themselves from sun exposure.

Design, setting and patients: We hypothesized that renal transplant recipients are at high risk to develop 25(OH)D deficiency. Serum 25(OH)D levels were analyzed in renal transplant patients with adequate renal function and in an age- and gender-matched control group (n = 31) at the end of winter. All renal transplant patients practiced solar UV-protection after transplantation. 25(OH)D levels were compared using a non parametrical test (Wilcoxon rank sum test).

Results: Serum 25(OH)D levels were significantly lower in renal transplant patients compared with controls (P = 0.007). Geometric mean (with 95% confidence interval) in renal transplant patients was 10.9 ng/ml (8.2-14.3) compared with 20.0 ng/ml (15.7-25.5) in the control group.

Conclusions: Renal transplant recipients are at high risk to develop 25(OH)D deficiency. Treatment with vitamin D is recommended to correct their vitamin D deficiency which may help protect them from serious vitamin D deficiency-related health problems that include an increased risk for internal malignancies.