Low vitamin D linked to endothelial dysfunction in diabetics
MedWire News: Type 2 diabetes patients with vitamin D deficiency have lower brachial flow-mediated dilation (FMD) and reduced levels of circulating endothelial progenitor cells (EPCs) than those with sufficient levels of vitamin D, say researchers.
Hung-Fat Tse (The University of Hong Kong, China) and colleagues suggest that this may help to explain previous suggestions of a link between low levels of vitamin D and increased cardiovascular disease risk in diabetics, as previously reported by MedWire News.
Tse and team report findings from 280 patients with Type 2 diabetes (mean age 68 years), 34.3% of whom had vitamin D deficiency (less than 20 ng/ml), which the researchers say suggests a possible link between low vitamin D levels and endothelial dysfunction.
Patients with vitamin D deficiency had a significantly lower brachial FMD (-1.43%) and reduced levels of CD34+/kinase insert domain-containing receptor EPCs (-0.12%) compared with those with normal vitamin D levels. These reductions remained valid after adjustment for age, gender, various cardiovascular risk factors, and glycated hemoglobin.
The researchers suggest that several mechanisms could account for the observed associations between vitamin D deficiency and endothelial dysfunction in patients with Type 2 diabetes.
They explain that vitamin D may improve endothelial nitric oxide synthase function and blunt the adverse effects of advanced glycation end-products on endothelial cells that can occur during hyperglycemia. Vitamin D also prevents the formation of foam cells in macrophages and reduces the up-regulation of key proinflammatory cytokines in diabetic patients.
The authors suggest that hyperparathyroidism, which can occur secondary to vitamin D deficiency, may exert a prosclerotic effect on vascular smooth muscle cells, which in turn, may contribute to endothelial dysfunction.
Tse and co-workers remark that "vitamin D deficiency is common and is associated with endothelial dysfunction and reduced EPC counts, independent of traditional cardiovascular risk factors in Type 2 diabetes mellitus patients."
They conclude in the Journal of Clinical Endocrinology and Metabolism: "The beneficial effects of vitamin D supplementation on endothelial function and EPC levels in deficient diabetes mellitus patients nonetheless need to be confirmed by future randomized controlled studies."
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By Helen Albert