Vitamin D supplementation: changes in bone mineral density in kidney transplant patients with long-term duration of the graft.

Background and Aims: In the medical literature, several studies have linked bone mineral density (BMD) with vitamin D deficiency in kidney transplant patients (KTRs). However, in spite of the fact that ergocalciferol, cholecalciferol and calcifediol reduce parathyroid hormone (PTH) and improves calcium levels, their effects on the bone mineral density (BMD) in KTRs remain undefined. In consideration of the lack of data available, we aim at investigating the effect of inactive form of vitamin D supplementation on the BMD over a follow-up period up to 2 year, in a real-life cohort of long-term kidney transplant(KT). Method: This study was carried out in KTRs who were followed up in a Nephrology Unit. Exclusion criteria were parathyroidectomy, therapy with bisphosphonate, previous history of bone fractures. Demographic, clinical and immunosuppressive agents were collected. Based on 25-OH-D levels, KTRs were classified as suffering from deficiency (< 30 ng/mL). BMD was evaluated at lumbar vertebral bodies (LV) and right femoral hip (FH) by a single operator, using a standard dual energy X-ray absorptiometry. According to WHO criteria, results were expressed as T-score (standard deviation [SD] relative to young healthy adults), and Z-score (SD relative to age-matched controls). Osteoporosis and osteopenia were defined as T score ≤ −2.5 SD and T score < −1 and > −2.5 SD, respectively. Laboratory data, 25-OH-D, and BMD were measured at baseline and after 24 months of supplementation therapy. Vitamin D deficiency was corrected using standard treatment strategy recommended for general population. Continuous variables were expressed as mean ± SD whereas categorical variables as percentage. The Student’s t test and chi-square test were used to compare to compare continuous and categorical variables, respectively. For before and after comparisons of continuous variables, the paired t-test or one-sample Wilcoxon signed rank test were used based on variable’s distribution. Results: Data pertaining to 111 out of 133 consecutive outpatients were collected, of whom most were males (69.4%), no-smokers (89.1%) and treated with glucocorticoids (84%). The mean age was 53.9±11.6 years and months after transplant was 161.6±128.3. No statistical differences were found among patients with normal BMD, osteopenia or osteoporosis at LV and FH in terms of age at transplant, gender distribution, time on dialysis, BMI and eGFR, serum calcium, serum phosphate, 25-OH-D and iPTH. At baseline, 25-OH-D was 13.9±7.2 ng/ml and the prevalence of osteopenia/osteoporosis was 40.9% (T-Score -1.69±0.37; Z-score -1.16±1.09) and 21.8 % (T-Score -3.15±0.50; Z-score -2.27±0.58) at LV; 55.3 % (T-Score -1.8±0.46; Z-score -0.84±0.633) and 14 % (T-Score -2.83±0.39; Z-score -1.65±0.49) at FH. After 27.6±3.7 months of therapy with cholecalciferol at mean dose of 13.396±7.537 UI at week, 25-OH-D values increased to 29.4±9.4 ng/ml (p<0.0001) while no statistically significant changes were found in Z-score and T-score at both sites, except for a mild improvement in lumbar vertebral Z-score, reaching −0.82± 0.7 (p = 0.06) in KTRs with osteopenia Conclusion: Our study showed BMD remained stable after up to 2 years of inactive vitamin D therapy in long-term kidney transplant with vitamin D deficiency. A mild increase in Z-score was observed in the L-spine. Further designated studies should be conducted to demonstrate the effect of vitamin D on BMD.