A recent study out of the United Kingdom was the first to investigate the effect of oral vitamin D supplementation on endothelial function in chronic kidney disease patients.
Cardiovascular disease (CD) is the most common cause of death in developing countries. Changes in the endothelium are often an early warning sign of the development of CD. The endothelium is a thin layer of cells that lines the interior of blood vessels. When it becomes dysfunctional it often causes changes in the amount of circulating biomarkers. As the disease progresses, flow in blood vessels becomes increasingly obstructed, which ultimately leads to cardiovascular events such as heart attack and stroke. Flow mediated dilation (FMD) of the brachial artery is often measured as an indicator of how much obstruction there is in the blood vessels.
Patients with chronic kidney disease (CKD) have three and a half times the risk of developing CD. Because low vitamin D is often associated with endothelial dysfunction and cardiovascular events in kidney patients, the authors of this study wanted to see if giving vitamin D to these patients could improve the early signs of endothelial dysfunction in stage 3 and 4 kidney patients.
Thirty-five patients were recruited into the study. Baseline 25(OH)D, brachial artery FMD, and biomarkers of endothelial functioning were measured. They were then given two doses of 300,000 IU of vitamin D3, once at baseline and once more at the end of the eight-week study.
The researchers were interested in if vitamin D supplementation would improve markers of endothelial function in these 35 patients with CKD.
The average 25(OH)D level improved from 17.2 ng/mL at baseline to 33.7 ng/mL. The brachial artery FMD increased, indicating improved blood flow in the blood vessels. E-selectin, ICAM-1, and VCAM-1, all markers of endothelial dysfunction, decreased. No signs of vitamin D toxicity were seen.
Several previous studies have shown improvements in FMD in stroke and diabetes patients. This is the first to show an improvement in FMD in CKD patients. The authors note that their positive results were likely due to the selection of vitamin D deficient patients who were then given a high treatment dose of vitamin D. They note that previous FMD studies with negative findings gave low doses of vitamin D to patients who were not vitamin D deficient.
This study is an important first step in the right direction to help prevent endothelial dysfunction in CKD patients, a high-risk group for CD. Vitamin D therapy decreased biomarkers of endothelial dysfunction while improving blood flow. The next step in research will be to compare vitamin D supplementation to a placebo to help determine if vitamin D directly leads to these effects in those with CKD.