Longitudinal follow-up of bone mineral density in children with nephrotic syndrome and the role of calcium and vitamin D supplements

Background. We previously have demonstrated that children with idiopathic nephrotic syndrome (INS) are at risk of metabolic bone disease (MBD). In this study, we report the longitudinal follow-up of these children and the role of calcium and vitamin D supplements. Methods. We prospectively studied 100 consecutive children with INS. They were treated with prednisone. All were subjected to a baseline clinical, biochemical and radiological evaluation. They were initiated on calcium (500 mg/day) and vitamin D-3 (200 IU/day) supplements, followed by a repeat assessment. The primary outcome measure was the Delta z score (difference between the initial and final z scores) on dual energy X-linked absorptiometry (DEXA). A univariate and multivariate analysis using stepwise linear regression was performed for factors predictive of an improved Delta z score. Results. Of the 88 children that completed the study, the majority (n = 54) had improved bone mineral density (BMD) at the spine, and another 25 children had stable BMD on calcium and vitamin D3 Supplements. The mean spinal BMD values were significantly better on follow-up (0.607 +/- 0.013 g/cm(2) as compared with baseline values (0.561 +/- 0.010 g/cm(2)) (P < 0.0001). The interval between initial and follow-up assessment was 1.5 +/- 0.07 years. Children who were on these supplements (n=73) had a significantly improved z score as compared with those who did not receive them (n=15) (P=0.008). On multivariate analysis, the factors predictive of an improved z score were: younger age (P<0.0001), calcium and vitamin D-3 supplement (P<0.0001), greater dietary calcium intake (P=0.022) and lower interval steroid dose (P = 0.001). Conclusions. Children with greater steroid doses were likely to have low BMD on follow-up. Calcium and vitamin D supplements may help in improving BMD in children with INS.