Studying the Effect of Vitamin D Supplementation on Vascular Function in CKD: A Work in Progress

I read with great interest the article “A randomized trial of vitamin D supplementation on vascular function in CKD” published by Kumar et al.1 in the Journal of the American Society of Nephrology. The study provided a clear demonstration of a beneficial effect of vitamin D supplementation on flow-mediated dilation (FMD).1 As the authors noted, this may mitigate the cardiovascular disease risk in CKD. However, I think the jury is still out about the consistency of the positive results shown in this study. For example, in contrast to the results of this study, a randomized clinical trial by Kendrick et al.2 showed no evidence of change in FMD in the brachial artery after 6 months of daily supplementation with cholecalciferol. Although the trial by Kendrick et al.2 did not compare cholecalciferol supplementation with a placebo group, the absence of dilation in response to either choleciferol or calcitriol was telling. I should also point out that there was a higher number of smokers in the trial by Kendrick et al.2 (approximately 49%) than in the trial by Kumar et al.1 (approximately 9%). Smoking is a known risk factor for arterial stiffness and cardiovascular disease.3 The Cardiovascular Health Study that investigated 5808 patients who were >65 years of age and had CKD revealed that traditional risk factors, including smoking, were associated with the largest absolute increases in risks for cardiovascular deaths among patients with CKD.3 I concur with the authors that the exclusion of patients with diabetes was a limitation of the study. This, of course, limits the generalizability to other populations, particularly because type 2 diabetes mellitus is the most common cause of CKD and ESRD worldwide.4 Incidentally, although the study by Kendrick et al.2 did include a high percentage of patients with diabetes (38%), there was no difference in the response of vitamin D on FMD by diabetes status. In conclusion, the finding of this study is important, because it may bring us closer to decreasing the scourge of cardiovascular morbidity and mortality frequently observed in patients with CKD. A broader and more diverse patient population will need to be studied to give us a more complete understanding of the effect of vitamin D on cardiovascular health in patients with CKD. Disclosures None.