Two Weeks of Watermelon Juice Supplementation Improves Nitric Oxide Bioavailability but Not Endurance Exercise Performance in Humans

Nitric Oxide. 2016 Sep 30;59:10-20. doi: 10.1016/j.niox.2016.06.008. Epub 2016 Jul 1.

Abstract

This study tested the hypothesis that watermelon juice supplementation would improve nitric oxide bioavailability and exercise performance. Eight healthy recreationally-active adult males reported to the laboratory on two occasions for initial testing without dietary supplementation (control condition). Thereafter, participants were randomly assigned, in a cross-over experimental design, to receive 16 days of supplementation with 300 mL·day(-1) of a watermelon juice concentrate, which provided ∼3.4 g l-citrulline·day(-1) and an apple juice concentrate as a placebo. Participants reported to the laboratory on days 14 and 16 of supplementation to assess the effects of the interventions on blood pressure, plasma [l-citrulline], plasma [l-arginine], plasma [nitrite], muscle oxygenation and time-to-exhaustion during severe-intensity exercise. Compared to control and placebo, plasma [l-citrulline] (29 ± 4, 22 ± 6 and 101 ± 23 μM), [l-arginine] (74 ± 9, 67 ± 13 and 116 ± 9 μM) and [nitrite] (102 ± 29, 106 ± 21 and 201 ± 106 nM) were higher after watermelon juice supplementation (P < 0.01). However, systolic blood pressure was higher in the watermelon juice (130 ± 11) and placebo (131 ± 9) conditions compared to the control condition (124 ± 8 mmHg; P < 0.05). The skeletal muscle oxygenation index during moderate-intensity exercise was greater in the watermelon juice condition than the placebo and control conditions (P < 0.05), but time-to-exhaustion during the severe-intensity exercise test (control: 478 ± 80, placebo: 539 ± 108, watermelon juice: 550 ± 143 s) was not significantly different between conditions (P < 0.05). In conclusion, while watermelon juice supplementation increased baseline plasma [nitrite] and improved muscle oxygenation during moderate-intensity exercise, it increased resting blood pressure and did not improve time-to-exhaustion during severe-intensity exercise. These findings do not support the use of watermelon juice supplementation as a nutritional intervention to lower blood pressure or improve endurance exercise performance in healthy adults.

Keywords: Blood pressure; Fatigue; Metabolism; Muscle oxygenation; Nitric oxide; l-arginine.

MeSH terms

  • Arginine / blood
  • Arterial Pressure
  • Blood Glucose / analysis
  • Citrulline / blood
  • Citrullus*
  • Dietary Supplements*
  • Fruit and Vegetable Juices*
  • Heart Rate
  • Humans
  • Lactic Acid / blood
  • Male
  • Malus
  • Nitric Oxide / analysis*
  • Nitrites / blood
  • Oxygen Consumption
  • Physical Endurance*
  • Pulmonary Gas Exchange
  • Young Adult

Substances

  • Blood Glucose
  • Nitrites
  • Citrulline
  • Nitric Oxide
  • Lactic Acid
  • Arginine