Relationship Among 25-Hydroxyvitamin D Concentrations, Insulin Action, and Cardiovascular Disease Risk in Patients With Essential Hypertension

There is substantial epidemiological evidence that low plasma concentrations of 25-hydroxyvitamin D (25(OH)D) are associated with increased risk of developing hypertension,1,2 although not all studies agree.3 Furthermore, analysis of data from the 2001–2004 National Health and Nutrition Examination Survey with linked mortality data through 2006 indicated that concentrations of 25(OH)D were inversely associated with all-cause and cardiovascular disease (CVD) mortality in the 2,609 participants with hypertension.4 There is also a coherent rationale for vitamin D deficiency to be associated with hypertension because it has been well documented that low vitamin D levels upregulate the renin-angiotensin-aldosterone system, increase inflammation, and cause endothelial dysfunction.5–7 However, thus far the results of interventional studies suggest that treatment with vitamin D neither substantially lowers blood pressure (BP) nor uniformly prevents CVD.8–10 The extensive literature is summarized in recent reviews.11,12 One possible explanation for this somewhat paradoxical situation is that considerable heterogeneity in CVD risk exists in patients with hypertension.13–15 More specifically, approximately 50% of patients with hypertension, treated or untreated, are insulin resistant and have the CVD risk factors usually associated with this abnormality.13 To the best of our knowledge, there is no available information regarding the relationship between 25(OH)D concentrations, specific measures of insulin action, and CVD risk factors in patients with hypertension. This study examines the relationships among these variables with the goal of providing new and clinically relevant information concerning the impact of insulin resistance and 25(OH)D concentrations on CVD risk in patients with hypertension.