Oral glucose loading acutely attenuates endothelium-dependent vasodilation in healthy adults without diabetes: An effect prevented by vitamins C and E

OBJECTIVES: The goal of this study was to determine whether postprandial hyperglycemia, induced by oral glucose loading, attenuates endothelial function in healthy subjects without diabetes and whether coadministration of vitamins C and E could prevent these postprandial changes. BACKGROUND: Epidemlologic evidence suggests that postprandial hyperglycemia, below diabetic levels, is a risk factor for cardiovascular disease. Postprandial hyperglycemia may promote atherosclerosis through endothelial dysfunction and oxidative stress. METHODS: We evaluated the acute effects of oral glucose loading (75 g), alone and with vitamins C (2 g) and E (800 IU), on endothelium-dependent flow-mediated dilation (FMD) of the brachial artery, in a randomized, double-blind, placebo-controlled, crossover study of 10 healthy volunteers. Changes in the levels of markers of oxidative stress (plasma malondialdehyde and erythrocyte glutathione, glutathione peroxidase and superoxide dismutase) were also assessed. RESULTS: Increases in plasma glucose and insulin after glucose loading were unaffected by vitamin coadministration. With glucose loading alone, FMD fell from 6.5 ± 2.2 at baseline to 5.4 ± 1.7, 3.7 ± 2.1* 4.1 ± 3.5* and 5.7 ± 1.9% at 1, 2, 3 and 4 h (*p < 0.05 vs. 0 h). In contrast, FMD did not change significantly after glucose plus vitamins (6.4 ± 1.3, 7.6 ± 1.8, 7.9 ± 2.7, 6.9 ± 2.3, 6.9 ± 1.9% at 0, 1, 2, 3 and 4 h). By two-way repeated measures analysis of variance we found a significant interaction between vitamin treatment and time (p = 0.0003), indicating that vitamins prevented the glucose-induced attenuation of FMD. Oxidative stress markers did not significantly change with glucose loading alone or with vitamins. CONCLUSIONS: Oral glucose loading causes an acute, transient decrease of FMD in healthy subjects without diabetes, which is prevented by vitamins C and E. (C) 2000 by the American College of Cardiology.