Watermelon's Blood Pressure Effect Only Works One Specific Way
The effect is real in the research — but only shows up with consistent daily intake, not the occasional slice.
Watermelon is one of the richest natural sources of L-citrulline, which the body converts to L-arginine and then nitric oxide — the same vessel-relaxing pathway behind beets' nitrate effect, arrived at through a different starting compound.
Key Findings
- Systolic blood pressure dropped by 4.02 mmHg, diastolic by 2.54 mmHg, across 15 trials
- The effect only showed up in people who already had elevated blood pressure
- Daily, ongoing intake beat single acute doses for vascular and performance benefits
- A single slice before a workout is not what the research actually tested
What the 2025 meta-analysis found
A 2025 meta-analysis pooling 15 randomized controlled trials and 415 participants found L-citrulline or watermelon supplementation significantly reduced systolic blood pressure by 4.02 mmHg and diastolic blood pressure by 2.54 mmHg, specifically in older adults.1
Who it actually worked for
A separate 2025 review found the antihypertensive effect showed up reliably in people who already had prehypertension or hypertension — but not in people whose blood pressure was already normal.2 Chronic, ongoing supplementation also produced more consistent vascular and exercise-performance benefits than a single acute dose.
Why the "pre-workout" framing is misleading
Watermelon and citrulline are often marketed as a same-day exercise boost. The research doesn't support that framing well — acute, single-dose intake doesn't reliably improve exercise tolerance. It's the sustained, daily pattern that shows the more consistent vascular effect.
The practical takeaway
- The effect is dose- and consistency-dependent — a single slice occasionally isn't what the trials tested
- Strongest evidence is for people with elevated blood pressure to begin with, not a general population effect
- Not a substitute for prescribed blood pressure medication — an additive dietary pattern, not a replacement
Sources
- "Does l-citrulline supplementation and watermelon intake reduce blood pressure in middle-aged and older adults?" ScienceDirect, 2025 meta-analysis. sciencedirect.com
- "Effects of L-citrulline supplementation and watermelon intake on arterial stiffness and endothelial function." Frontiers in Nutrition, 2025. frontiersin.org
