Effect of oral vitamin E (α-tocopherol) supplementation on vascular endothelial function in Type 2 diabetes mellitus

Aims Vascular endothelial dysfunction, an early marker of atherosclerosis, has been demonstrated in Type 2 diabetes mellitus (DM). Vitamin E preserves endothelial function in animal models of diabetes and reduces cardiovascular risk. We examined endothelial function and the effect of vitamin E supplements in uncomplicated Type 2 DM. Methods Forty-eight subjects with Type 2 DM and 21 controls had endothelial function assessed using forearm venous occlusion plethysmography with endothelium-independent (sodium nitroprusside) and dependent (acetylcholine, bradykinin) vasodilators. Those with diabetes received 1600 iu daily oral alpha-tocopherol or placebo, double-blind for 8 weeks, and had endothelial function reassessed. Results The diabetic group had higher HbA(1c) (6.9 +/- 1.4 vs 4.8 +/- 0.6%; P < 0.01) and systolic (145 +/- 15 vs 130 +/- 16 mmHg; P < 0.01) but not diastolic blood pressure (79 +/- 8 vs 76 +/- 9 mmHg; P = 0.15). There was blunted vasodilation to acetylcholine (15 mu g/min; P < 0.01) in subjects with diabetes. Vasodilation to sodium nitroprusside and bradykinin was similar (all P > 0.1). alpha-tocopherol did not affect vasodilation to nitroprusside (P > 0.1), acetylcholine (P > 0.1)or bradykinin (P > 0.1). Conclusions There may be receptor-specific endothelial dysfunction in subjects with uncomplicated Type 2 DM. This is not improved by treatment with alpha-tocopherol.