title: Two weeks of watermelon juice supplementation improves nitric oxide bioavailability but not endurance exercise performance in humans.
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.
authors.affiliation: Sport and Health Sciences, St. Luke's Campus, University of Exeter, Heavitree Road, Exeter, EX1 2LU, United Kingdom. Electronic address: S.J.Bailey@exeter.ac.uk.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Bailey
authors.affiliation: Sport and Health Sciences, St. Luke's Campus, University of Exeter, Heavitree Road, Exeter, EX1 2LU, United Kingdom.
authors.forename: Jamie R
authors.initials: JR
authors.lastname: Blackwell
authors.affiliation: Sport and Health Sciences, St. Luke's Campus, University of Exeter, Heavitree Road, Exeter, EX1 2LU, United Kingdom.
authors.forename: Ewan
authors.initials: E
authors.lastname: Williams
authors.affiliation: Sport and Health Sciences, St. Luke's Campus, University of Exeter, Heavitree Road, Exeter, EX1 2LU, United Kingdom.
authors.forename: Anni
authors.initials: A
authors.lastname: Vanhatalo
authors.affiliation: Sport and Health Sciences, St. Luke's Campus, University of Exeter, Heavitree Road, Exeter, EX1 2LU, United Kingdom.
authors.forename: Lee J
authors.initials: LJ
authors.lastname: Wylie
authors.affiliation: Exeter Medical School, St. Luke's Campus, University of Exeter, Heavitree Road, Exeter, EX1 2LU, United Kingdom.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Winyard
authors.affiliation: Sport and Health Sciences, St. Luke's Campus, University of Exeter, Heavitree Road, Exeter, EX1 2LU, United Kingdom.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Jones
mesh_terms: D001120:Arginine / Q000097:blood; D062186:Arterial Pressure; D001786:Blood Glucose / Q000032:analysis; D002956:Citrulline / Q000097:blood; D029773:Citrullus; D019587:Dietary Supplements; D000067030:Fruit and Vegetable Juices; D006339:Heart Rate; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D027845:Malus; D009569:Nitric Oxide / Q000032:analysis*; D009573:Nitrites / Q000097:blood; D010101:Oxygen Consumption; D010807:Physical Endurance; D011659:Pulmonary Gas Exchange; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D009573:Nitrites; D002956:Citrulline; D009569:Nitric Oxide; D019344:Lactic Acid; D001120:Arginine
keywords: Blood pressure; Fatigue; Metabolism; Muscle oxygenation; Nitric oxide; l-arginine