Effect of Muscadine Grape Seed Supplementation on Vascular Function in Subjects with or at Risk for Cardiovascular Disease: A Randomized Crossover Trial

Background: Muscadine grape seeds have high concentrations of polyphenolic compounds with antioxidant and other properties that would be expected to have favorable effects on endothelial function. Objectives: To evaluate the effect of muscadine grape seed supplementation on endothelial function and cardiovascular risk factors in subjects with increased cardiovascular risk. Design: In a randomized, double-blind, placebo-controlled crossover trial, 50 adults with coronary disease or >= 1 cardiac risk factor received muscadine grape seed supplementation (1300 mg daily) and placebo for 4 weeks each, with a 4-week washout. Resting brachial diameter and brachial flow-mediated dilation (FMD) and biomarkers of inflammation, lipid peroxidation, and antioxidant capacity were determined at the beginning and end of each period and compared in mixed linear models. Results: There was no evidence of improved FMD (% change) with muscadine grape seed (muscadine grape seed: pre 5.2% +/- 0.3%, post 4.6% +/- 0.3%, p = 0.06; placebo: pre 5.3% +/- 0.4%, post 5.2% +/- 0.4%, p = 0.82; p for muscadine grape seed vs. placebo = 0.25). However, there was a significant increase in baseline diameter (mm) with muscadine grape seed,supplementation (muscadine grape seed: pre 4.05 +/- 0.09, post 4.23 +/- 0.10, p = 0.002; placebo: pre 4.12 +/- 0.11, post 4.12 +/- 0.10, p = 0.93; p for muscadine grape seed vs. placebo = 0.026). All other biomarkers were not significantly altered by muscadine grape seed supplementation. Conclusions: Four weeks of muscadine grape seed supplementation in subjects with increased cardiovascular risk did not produce a statistically significant increase in brachial flow-mediated vasodilation or a significant change in other biomarkers of inflammation, lipid peroxidation, or antioxidant capacity. However, the muscadine grape seed supplement did result in a significant increase in resting brachial diameter. The clinical significance of the effect on resting diameter is not yet established. More research is warranted to fully characterize the vascular effects of this and other grape-derived nutritional supplements and to determine whether these vascular effects translate into important clinical benefits.