Vitamin D Supplementation in Chronic Kidney Disease: A Systematic Review and Meta-Analysis of Observational Studies and Randomized Controlled Trials

Background and objectives Vitamin D deficiency is highly prevalent among patients with chronic kidney disease (CKD). The benefits and harms of vitamin D supplementation (ergocalciferol or cholecalciferol) were assessed in patients with nondialysis-dependent CKD, dialysis-dependent CKD, and renal transplant recipients. Design, setting, participants, & measurements MEDLINE (1966 to September 2009), SCOPUS (September 2009), and nephrology conference proceedings were searched for relevant observational and randomized controlled trials (RCTs). Treatment effects were summarized as mean differences (MDs) with 95 % confi-dence intervals (CIs) using a random effects model. Separate analyses were conducted for observational studies and RCTs. Results Twenty-two studies (17 observational and 5 RCTs) were included. There was a significant improve-ment in 25-hydroxyvitamin D (MD 24.1 ng/ml, 95 % CI 19.6 to 28.6) and an associated decline in parathy-roid hormone (PTH) levels (MD 41.7 pg/ml, 95 % CI 55.8 to 27.7) among observational studies. PTH reduction was higher in dialysis patients. Among RCTs, there was a significant improvement in 25-hy-droxyvitamin D (MD 14 ng/ml, 95 % CI 5.6 to 22.4) and an associated decline in PTH levels (MD 31.5 pg/ ml, 95 % CI 57 to 6.1). A low incidence of hypercalcemia and hyperphosphatemia was reported with vi-tamin D supplementation. Cardiovascular and skeletal effects of vitamin D supplementation have not been studied. Included studies were mostly of low to moderate quality. Conclusions Available evidence from low-to-moderate quality observational studies and fewer RCTs sug-gests that vitamin D supplementation improves biochemical endpoints. However, whether such improve-ments translate into clinically significant outcomes is yet to be determined