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Watermelon

Watermelon

Best for

Improve nitric oxide balance

Not enough research 2–4 weeks 3 studies, n=34

  • 12 papers
  • 1 of 47 outcomes
  • 1 positive

Watermelon does not have enough research to establish a reliable benefit for vascular function, although small human studies provide an early signal involving blood pressure and nitric oxide-related measures.

Median effective dose, most-studied outcomes

  • Promote easier vessel relaxation 90 g 4 wk
Full protocol, 3 outcomes

Risk, worst reported severity

  • skin rash mild

What watermelon actually does

Outcome Effect Evidence Dose Time Rank
Early research 1
Improve nitric oxide balance Not enough research Nitric oxide helps blood vessels relax and maintain healthy circulation.
— 		4 RCTs 3 papers · n=34 — 2–4 wk —

Effect tiers come from native-unit MCID where available, Cohen's d otherwise.

Protocol

Dose, timing & forms

How much

The clearest, though still preliminary, human signal comes from vessel-function research using food-scale watermelon amounts over several weeks. Trials examined roughly 90 to 304 g daily for four weeks, with changes in some blood-pressure and blood-vessel measures.12 Exercise and antioxidant research is much less convincing so far, so there is no evidence-based reason to chase larger doses for performance or antioxidant effects.

When and how long

Treat watermelon as a daily food or juice habit, not an occasional pre-workout trick. The vascular trials used consistent intake across weeks, which fits the idea that citrulline availability needs repeated exposure rather than one serving before a workout.12 If juice bothers your stomach, take it with a meal or split it into smaller servings.

Forms & standardisation

Fresh watermelon, juice, and watermelon-derived preparations are not interchangeable. The strongest human trial coverage centers on watermelon products that supply citrulline, rather than a widely validated standardized extract, so look for a label that states both the watermelon amount and citrulline content.12 Juice also brings carbohydrate and calories, which matter if you use it regularly.

Studied range, by outcome

Outcome Studied range Median effective Duration Evidence
Promote easier vessel relaxation — 90 g 4 wk 2 papers 4 sig. endpoints
Support overall antioxidant capacity 14.4 mg — 4 wk 2 papers
Sustain more output for longer 710 mL — 8 wk 1 paper

Adverse events and drug interactions

Safety events

skin rash mild
In context

What this is and how it works

  • Three small studies (n=34) assessed nitric oxide-related vascular outcomes, but no reliable effect size establishes noticeable benefit.1
  • Twelve papers reviewed here span 47 outcomes, with evidence concentrated in early vascular research.
  • Evidence mainly involves adults with prehypertension or obesity using watermelon juice or extract, limiting broader conclusions.

Watermelon is the juicy red fruit of Citrullus lanatus. Beyond water, sugar, and lycopene, it naturally contains citrulline, an amino acid that gives watermelon juice and extracts their supplement appeal. Research has tested both food-based watermelon products and more concentrated preparations.12

Citrulline acts like a delivery truck bringing raw material to your body's nitric oxide factory: your body converts it to arginine, which it then uses to produce nitric oxide. Nitric oxide signals the smooth muscle around blood vessels to loosen, a process researchers measured through blood pressure and vessel-wave markers in small watermelon trials.12

Bottom line

Watermelon makes sense if you enjoy it as food and want a low-stakes way to add citrulline to your diet. Small trials suggest a possible vascular signal, but they do not establish a reliable supplement benefit, and performance claims have not held up in the reviewed evidence.12 Skip concentrated products if you expect a proven workout enhancer, and stop use if you develop a skin rash.

Frequently asked

Common questions

Does watermelon increase nitric oxide?

Watermelon provides citrulline, an amino acid your body uses to make arginine, which supplies the raw material for nitric oxide. Small human trials tracked improvements in some vessel-related measures, but the evidence remains too limited to establish a reliable nitric oxide benefit. 12

Is watermelon juice useful before exercise?

One small athlete study examined watermelon juice for exercise-related muscle soreness, but it does not establish a dependable performance boost. The reviewed longer exercise trials also did not show a significant improvement in sustained output. 3

Is watermelon extract better than eating watermelon?

The human vascular studies used watermelon products that delivered concentrated fruit components, while other work used juice. A supplement label should clearly state the amount of watermelon material and citrulline it provides, because “watermelon extract” alone does not tell you the active dose. 12

Sources

Sources

  1. 1. Effects of watermelon supplementation on aortic blood pressure and wave reflection in individuals with prehypertension: a pilot study (2012) ↑
  2. 2. Watermelon extract supplementation reduces ankle blood pressure and carotid wave reflection in obese adults with prehypertension: preliminary study (2011) ↑
  3. 3. Watermelon juice: potential functional drink for sore muscle relief in athletes (2013) ↑

Generated August 27, 2026

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