Summary
Researchers explored whether watermelon juice—rich in citrulline, a precursor to arginine and nitric oxide (NO)—could protect the blood vessels from the harmful effects of acute hyperglycemia. In this randomized, double-blind, placebo-controlled crossover trial, 17 healthy adults consumed either 500 mL of watermelon juice or a calorie-matched placebo each day for two weeks before undergoing an oral glucose tolerance test. Vascular function was assessed using flow-mediated dilation (FMD) and measures of microvascular blood flow via near-infrared spectroscopy. After the watermelon juice phase, participants showed significantly better endothelial function: postprandial FMD was higher, microvascular blood flow increased, and baseline tissue oxygen saturation improved compared with the placebo condition. These findings suggest that short-term watermelon juice supplementation enhances both macro- and microvascular function during spikes in blood glucose, likely through increased NO production from citrulline and possibly through antioxidant or other bioactive compounds in the juice. Overall, regular intake of watermelon juice helped counteract glucose-induced vascular dysfunction in healthy young adults.
PMID: 34510203
PMCID: PMC8562079
DOI: 10.1093/jn/nxab279
Abstract
Background
Acute hyperglycemia reduces NO bioavailability and causes macro- and microvascular dysfunction. Watermelon juice (WMJ) is a natural source of the amino acid citrulline, which is metabolized to form arginine for the NO cycle and may improve vascular function.
Objectives
We examined the effects of 2 weeks of WMJ compared to a calorie-matched placebo (PLA) to attenuate acute hyperglycemia-induced vascular dysfunction.
Methods
In a randomized, placebo-controlled, double-blind, crossover trial, 6 men and 11 women (aged 21-25; BMI, 23.5 ± 3.2 kg/m2) received 2 weeks of daily WMJ (500 mL) or a PLA drink followed by an oral-glucose-tolerance test. Postprandial flow-mediated dilation (FMD) was measured by ultrasound (primary outcome), while postprandial microvascular blood flow (MVBF) and ischemic reperfusion were measured by near-infrared spectroscopy (NIRS) vascular occlusion test (VOT).
Results
The postprandial FMD area AUC was higher after WMJ supplementation compared to PLA supplementation (838 ± 459% · 90 min compared with 539 ± 278% · 90 min; P = 0.03). The postprandial MVBF (AUC) was higher (P = 0.01) following WMJ supplementation (51.0 ± 29.1 mL blood · 100 mL tissue-1 · min-1 · 90 min) compared to the PLA (36.0 ± 20.5 mL blood · 100 mL tissue-1 · min-1 · 90 min; P = 0.01). There was a significant treatment effect (P = 0.048) for WMJ supplementation (71.2 ± 1.5%) to increase baseline tissue oxygen saturation (StO2%) when compared to PLA (65.9 ± 1.7%). The ischemic-reperfusion slope was not affected by WMJ treatment (P = 0.83).
Conclusions: Two weeks of daily WMJ supplementation improved FMD and some aspects of microvascular function (NIRS-VOT) during experimentally induced acute hyperglycemia in healthy adults. Preserved postprandial endothelial function and enhanced skeletal muscle StO2% are likely partially mediated by increased NO production (via citrulline conversion into arginine) and by the potential antioxidant effect of other bioactive compounds in WMJ.
Vincellette CM, Losso J, Early K, Spielmann G, Irving BA, Allerton TD. Supplemental Watermelon Juice Attenuates Acute Hyperglycemia-Induced Macro-and Microvascular Dysfunction in Healthy Adults. J Nutr. 2021 Nov 2;151(11):3450-3458. doi: 10.1093/jn/nxab279. PMID: 34510203; PMCID: PMC8562079.