THE EFFECT OF VITAMIN D ON BONE MINERAL DENSITY: A REAL-LIFE STUDY IN LONG-TERM KIDNEY TRANSPLANT RECIPIENTS NEVER SUPPLEMENTED

Background and Aims: Vitamin D insufficiency has been associated to reduced bone mineral density (BMD) in kidney transplant patients (KTRs). However, data of vitamin D supplementation on BMD is still conflicting especially for long-term KTRs. The purpose of our study is to ascertain the effect of 25-OH-vitamin D (25-OH-D) supplementation on the BMD over a follow-up period up to 3 years, in a real-life cohort of long-term KTRs never supplemented with 25-OH-D and no treated with active vitamin D, bisphosphonate and calciomimetics. Method: Demographic, clinical and laboratory data were collected. Inclusion criteria were: 1) being a recipient of a kidney from a cadaveric or living donor; 2) age ≥ 18 years; 3) no therapy with inactive vitamin D sterols. Patients with parathyroidectomy, and/or history of bone fractures were excluded. BMD was evaluated with standard DEXA, performed at baseline (before vitamin D supplementation) and at the end of study period. BMD was assessed at lumbar vertebral bodies (LV) and right femoral neck (FN) by a single operator. Bone mineral content (BMC) was calculated in grams (g), bone area in centimetres squared (cm2), and BMD in g/cm2 (BMC divided by the area). 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. According to plasma levels, 25-OH-D was supplemented as recommended for general population. Linear mixed model analysis was implemented to test the impact of 25-OH-D use on Z-score, T-score and BMD changes (dependent variables) adjusted for sex, age, BMI and presence of diabetes. Z-score, T-score and BMD changes were defined as Z-score, T-score and BMD at follow-up – Z-score, T-score and BMD at study inception. Results: 107 KTRs consecutive outpatients never supplemented with 25-OH-D were enrolled. 42 KTRs treated with bisphosphonate (n. 13) and/or calcio-mimetics (n. 11) and/or active vitamin D (n. 29) were considered as control group. Clinical and biochemical characteristics are shown in Table 1. The mean study-period was 27.7±3.4 months. Dexa data were reported in Table 2. At linear mixed model analysis, a positive interaction of 25-OH-D supplementation on T-score and Z-score changes at lumbar vertebral bodies was found (p<0.05). At the end of the study, no statistical differences in Z-score, T-score and BMD gains were observed. Conclusion: Prolonged supplementation with 25-OH-D effects on Z-score and T-score at LV in long-term KTRs never supplemented.