Relationship among 25-hydroxyvitamin D concentrations, insulin action, and cardiovascular disease risk in patients with essential hypertension

Abstract

Background Although low plasma 25-hydroxyvitamin D (25(OH)D) concentrations have been shown to predict risk of hypertension and associated cardiovascular disease (CVD), vitamin D repletion has not consistently lowered blood pressure or decreased CVD. One possibility for this discrepancy is the presence of considerable metabolic heterogeneity in patients with hypertension. To evaluate this possibility, we quantified relationships among insulin resistance, 25(OH)D concentration, and CVD risk factor profile in patients with essential hypertension. Methods Measurements were made of 25(OH)D concentrations, multiple CVD risk factors, and insulin resistance by the steady-state plasma glucose concentration during the insulin suppression test in 140 otherwise healthy patients with essential hypertension. Results As a group, the patients were overweight/obese and insulin resistant and had low 25(OH)D concentrations. The more insulin resistant the patients were, the worse the CVD risk profile was. In addition, the most insulin-resistant quartile had significantly lower 25(OH)D concentrations than the most insulin-sensitive quartile (20.3±1.4 vs. 25.8±1.4ng/ml; P = 0.005). In the entire group, 25(OH)D concentration significantly correlated with magnitude of insulin resistance (steady-state plasma glucose concentration; r =-0.20; P = 0.02). Conclusions There was considerable metabolic heterogeneity and substantial difference in magnitude of conventional CVD risk factors in patients with similar degrees of blood pressure elevation. The most insulin-resistant quartile of subjects had the lowest 25(OH)D concentration and the most adverse CVD risk profile, and they may be the subset of patients with essential hypertension most likely to benefit from vitamin D repletion.