Chronic Intake of Onion Extract Containing Quercetin Improved Postprandial Endothelial Dysfunction in Healthy Men

Abstract

Background: Epidemiologic studies have shown that dietary flavonoids reduce the risk of cardiovascular events. Onion is rich in quercetin, a strong antioxidant flavonoid. In some in vitro studies, quercetin improved endothelial function associated with atherosclerosis, a leading cause of cardiovascular events.

Objective: The aim of this study was to determine whether chronic onion extract intake would improve postprandial endothelial dysfunction induced by an oral maltose load in healthy men.

Methods: Healthy men (44 ± 10 years, n = 23) received 4.3 g of onion extract (containing 51 mg of quercetin) once a day for 30 days. Before and after the chronic onion extract intake, fasting and postprandial flow-mediated vasodilation (FMD) responses were measured.

Results: Maltose loading significantly decreased FMD both before and after chronic onion extract intake (p = 0.000037 and p = 0.0035, respectively). The chronic onion extract intake did not significantly affect fasting FMD (p = 0.069) but improved the postprandial FMD significantly from 5.1% ± 2.2% to 6.7% ± 2.6% (p = 0.00015). The chronic onion extract intake did not alter systemic and forearm hemodynamics.

Conclusion: These findings suggest that chronic onion extract intake ameliorates postprandial endothelial dysfunction in healthy men and may be beneficial for improving cardiovascular health.

Key words:

• onion
• quercetin
• endothelial function
• postprandial hyperglycemia
• flow-mediated vasodilation
• prevention
• cardiovascular events

ACKNOWLEDGMENTS

The authors thank Muneaki Tomotake and Yasuharu Hashimoto for preparation of the onion juice powder; Takuya Hamano, Shintaro Ide, and Shoichi Ueno for assistance in the preparation of materials for the institutional review; and Chiaki Megumi, Yohei Koyama, Shohei Hoshino, Keiko Taketani, Hiroshi Sasako, and Yusuke Kohama for assistance in various stages of the study.

This article was presented at the 76th Annual Scientific Meeting of the Japanese Circulation Society in Fukuoka, Japan, 2012.

This study was supported by House Foods Corporation. H. Nakayama, N. Tsuge, and H. Sawada are employees of House Foods Corporation. Y. Higashi has no conflicts of interest.

Abbreviation: FMD = flow-mediated vasodilation.