A recent narrative review in Nutrients evaluated the cardiovascular benefits of L-citrulline, an amino acid abundant in watermelon, particularly in the rind.
Researchers in Brazil synthesized evidence on whether watermelon could serve as a natural alternative or complement to commercial L-arginine supplementation, since L-citrulline is converted to L-arginine in the kidneys, promoting nitric oxide (NO) production.
The review found that watermelon effectively increases L-citrulline and L-arginine levels, enhancing NO synthesis—a molecule critical for relaxing blood vessels. This mechanism may improve vascular function and blood pressure, offering a potentially safe, nutritional strategy for individuals with impaired endothelial function.
Therapeutic effects generally require more than 2–3 grams per day of L-citrulline, which is difficult to achieve through fresh fruit alone, making concentrated watermelon extracts or powders more practical.
Understanding the Mechanism
L-citrulline from watermelon is converted to L-arginine in the kidneys. L-arginine is a precursor for NO, which dilates blood vessels, reduces arterial stiffness, and mitigates inflammation. Endothelial dysfunction—chronic damage to blood vessel linings—impairs NO production and is a known contributor to cardiovascular disease (CVD).
While oral L-arginine supplements are widely available, much is metabolized before reaching systemic circulation, limiting efficacy. Watermelon provides a bioavailable alternative by bypassing liver degradation, efficiently boosting NO levels.
Clinical Evidence
The review highlights that populations with elevated blood pressure, obesity, or endothelial dysfunction benefit most from watermelon supplementation. Clinical trials using concentrated watermelon powder delivering ~4 g L-citrulline daily have shown significant reductions in blood pressure and arterial stiffness over six weeks.
In contrast, healthy individuals or those consuming low-dose watermelon juice often show minimal vascular improvements. Additional compounds in watermelon, such as lycopene and polyphenols, may further support vascular health through antioxidant and anti-inflammatory effects.
Limitations and Future Directions
Despite promising findings, evidence remains limited. Most studies are short-term, use varying doses, and rely on different formulations, preventing definitive conclusions.
Watermelon cannot replace pharmacological blood pressure treatment but may serve as a complementary dietary strategy, especially for at-risk populations. Future research should explore long-term outcomes, dose-response relationships, and efficient delivery methods, such as rind powder, to achieve clinically relevant L-citrulline levels sustainably.
Conclusion
Watermelon, due to its high L-citrulline content, offers a practical, food-based approach to supporting cardiovascular health. By enhancing L-arginine and NO production, it may help manage blood pressure and improve vascular function, particularly in individuals with preexisting vascular risk factors. However, further robust clinical trials are necessary to establish firm recommendations.
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