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More research needed to evaluate role of vitamin D in reducing CVD
McGreevy C. Ann Intern Med. 2011;155:820-826.
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Emerging evidence suggests that vitamin D deficiency, CVD and endothelial dysfunction are linked by biological associations. However, few randomized controlled trials have studied the effect of vitamin D supplementation on CV risk, leading to a call for more research to evaluate the role of vitamin D supplementation in heart diseases.
“Despite some concerns that vitamin D may merely be a surrogate marker for poor health status, further studies are needed to evaluate the efficacy of vitamin D supplementation,” Cora McGreevy, MB, BCh, BAO, and David Williams, MB, BAO, BCh, PhD, both of the Royal College of Surgeons in Ireland at Beaumont Hospital, wrote in a review published in Annals of Internal Medicine. “These trials should aim to test the hypotheses generated by observational studies and provide evidence on whether vitamin D supplementation may play a role in CV protection.”
The definition of vitamin D deficiency remains controversial. According to the International Osteoporosis Foundation, vitamin D insufficiency is a 25-hydroxyvitamin D, or 25-(OH)D, level of less than 50 nmol/L and vitamin D deficiency is a 25(OH)D level of less than 25 nmol/L. However, there is no universal consensus on which serum level dictates optimum vitamin D status.
Vitamin D deficiency is prevalent worldwide, particularly among residents living in northern latitudes and in Northern Europe, Africa and the Middle East (see Sidebar for other risk factors).
“Many observational studies have reported inverse relationships between serum 25-(OH)D levels and the risk for a wide range of conditions, including vascular disease, autoimmune disease, type 2 diabetes, obesity and cognitive impairment,” McGreevey and Williams wrote.
The reviewers also examined evidence to date on the possible links between vitamin D deficiency and supplementation on CV outcomes. However, results have been “contradictory and inconclusive,” they said.
McGreevy and Williams said until further research is complete, vitamin D cannot be recommended as a treatment for CVD.
Disclosure: Dr. Williams is on the advisory board for Boehringer Ingelheim and Dr. McGreevy received payment for lectures from MSD.
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Observational research has shown an association between vitamin D levels and cardiovascular outcomes, and there is some scientific rationale for this. However, it remains unclear what the "optimal" vitamin D level is for CV health. Once that is determined, the next critical question is whether exogenous supplementation of vitamin D - and in what form - to achieve that level will result in better clinical outcomes. Unfortunately, for many other vitamins and supplements, for example vitamin E and other 'anti-oxidant' vitamins, there was similar enthusiasm for supplementation to improve CV outcomes based on observational research and mechanistic appeal. When tested in randomized clinical trials, [these vitamins showed] no benefit and, in some cases, increased mortality with supplementation. Only well-designed, well-conducted, placebo controlled randomized clinical trials can give us the answer to this question for vitamin D. Until then, we must act upon the lessons learned from previous vitamin supplementation trials; it is premature to encourage supplementation of vitamin D to improve CV outcomes without evidence from randomized clinical trials.
– L. Kristin Newby, MD
Professor of
Medicine, Cardiology
Duke University
Disclosures: Dr. Newby reports no relevant financial disclosures.
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