Watermelon contains two compounds with genuine relevance to prostate health: lycopene, a pigment that gives the flesh its red color, and L-citrulline, an amino acid that supports blood flow. The evidence behind lycopene and prostate cancer risk has been building for decades, and more recent work suggests benefits for non-cancerous prostate enlargement as well. But the relationship between eating watermelon and protecting your prostate is more nuanced than “eat more and you’re covered,” and some of the strongest-sounding claims outrun what the science actually shows.
Watermelon’s Lycopene Is Unusually Easy to Absorb
Most conversations about lycopene and the prostate start with tomatoes, and for good reason: tomato products were the first lycopene source studied extensively. But watermelon deserves separate attention because of how its lycopene is packaged. Lycopene exists in different geometric forms, and the form found predominantly in watermelon (the cis-isomer) is the same form your body actually absorbs and uses. Tomatoes contain mostly the trans-isomer, which needs heat processing to convert into the more bioavailable cis form. Watermelon delivers the cis form naturally, without cooking.1PubMed Central. Watermelon lycopene and allied health claims
A crossover study confirmed this matters in practice. Participants who drank fresh-frozen watermelon juice reached plasma lycopene levels comparable to those who drank canned tomato juice, even though the tomato juice had undergone the heat processing typically needed to boost lycopene absorption. When the watermelon dose was doubled, blood levels didn’t rise proportionally, suggesting the body hits a ceiling for how much it can take up at once.2The Journal of Nutrition. Consumption of Watermelon Juice Increases Plasma Concentrations of Lycopene and β-Carotene in Humans The practical takeaway is that you don’t need to eat enormous quantities; a regular serving of red-fleshed watermelon gets lycopene into your bloodstream about as effectively as a serving of tomato sauce.
How Lycopene Interacts with Prostate Cancer Cells
Laboratory work has mapped out several ways lycopene appears to interfere with prostate cancer cell growth. In cell-culture experiments using human prostate cancer cell lines, lycopene treatment slowed the cell cycle, essentially putting the brakes on division. It also promoted apoptosis, the self-destruct sequence that healthy cells use to remove damaged copies of themselves but that cancer cells often disable. The effect was dose-dependent: more lycopene meant more cells stuck in the resting phase and fewer actively replicating.3PubMed Central. The Potential Role of Lycopene for the Prevention and Therapy of Prostate Cancer: From Molecular Mechanisms to Clinical Evidence
Beyond simply acting as an antioxidant, lycopene appears to influence signaling pathways that prostate cancer cells rely on. Research on primary human prostate cells found that proteins involved in androgen receptor signaling, growth inhibition, and cell defense responses were among those most affected by lycopene exposure.4PubMed Central. Effects of lycopene on protein expression in human primary prostatic epithelial cells A separate review noted that lycopene suppressed proliferation and modulated the relevant signaling pathways both in living animals and in isolated cells.5Biomedicine & Pharmacotherapy. Potential inhibitory effect of lycopene on prostate cancer
Cell and animal studies are not proof that eating watermelon prevents cancer in a person. But they do establish plausible biological mechanisms rather than just a statistical association. Lycopene doesn’t just happen to correlate with lower risk; researchers can point to specific molecular events that explain why it might matter.
What the Human Evidence Shows for Prostate Cancer Risk
The most convincing human evidence comes from prospective cohort studies, where researchers track what large groups of people eat and then follow them for years to see who develops prostate cancer. A large cohort study that tracked men at high cardiovascular risk found that those in the highest quarter of lycopene intake had roughly half the prostate cancer risk compared to those in the lowest quarter. The risk reduction became significant at lycopene intakes above about 5 mg per day, where risk dropped by about two-thirds.6PubMed Central. Lycopene intake and prostate cancer risk in men at high cardiovascular risk: a prospective cohort study
An earlier and widely cited study following tens of thousands of male health professionals over 12 years also found that men with the highest lycopene intake had a lower risk of prostate cancer, with a roughly 16% reduction comparing the top and bottom fifths of intake.7JNCI: Journal of the National Cancer Institute. A Prospective Study of Tomato Products, Lycopene, and Prostate Cancer Risk The effect sizes differ between studies, which is expected given different populations, follow-up periods, and methods of measuring intake. But the direction of the finding has been consistent: more lycopene, less prostate cancer.
A fair caveat: these are observational findings, not randomized trials. Men who eat more lycopene-rich foods probably differ from those who don’t in ways researchers can’t fully account for. They may exercise more, eat better overall, or have access to better healthcare. No one has run a large randomized trial giving one group watermelon and another group a placebo for a decade to watch prostate cancer rates. That kind of trial is expensive and logistically brutal. So the evidence sits in the frustrating middle ground of “strong and consistent, but not definitive.”
Benign Prostate Enlargement
Prostate cancer gets the headlines, but benign prostatic hyperplasia, the non-cancerous swelling of the prostate that affects most men as they age, is far more common. It’s the condition behind the weak stream, nighttime bathroom trips, and feeling like you can never quite empty your bladder. Lycopene has been studied here too, and the results are intriguing if not yet overwhelming.
A six-month trial compared lycopene supplementation against placebo in men with BPH. The lycopene group saw a decrease in PSA levels and no measurable growth in prostate size, while the placebo group’s prostates continued to enlarge. Symptom scores improved in both groups, but the improvement was larger in the lycopene group.8PubMed. Lycopene inhibits disease progression in patients with benign prostate hyperplasia That’s a promising result from a relatively small study.
A systematic review that pooled data from multiple trials found a slight reduction in BPH diagnosis with lycopene, but the reduction wasn’t statistically significant.9Maturitas. Lycopene and the prevention and treatment of benign prostatic hyperplasia and prostate cancer: a systematic review and meta-analysis This reflects the common pattern in nutrition research: individual studies can look impressive, but when you combine them all, the signal weakens because study designs and populations vary. A more recent multicenter study compared a supplement containing lycopene (combined with saw palmetto extract and selenium) against a standard prescription drug for urinary symptoms. Both groups saw similar improvements in urine flow rate and symptom scores, though the drug group experienced more sexual side effects.10PubMed Central. Comparison of Serenoa repens, lycopene, and selenium versus dutasteride for the treatment of LUTS/BPH That’s worth noting for men who want to try a dietary approach before committing to medication, though the supplement in that study was a combination product, so you can’t attribute the entire effect to lycopene alone.
The PSA Question
PSA (prostate-specific antigen) is the blood marker most men encounter during prostate screening. A lower PSA is generally reassuring, and the individual BPH trial described above found that lycopene supplementation reduced it. But a systematic review and meta-analysis that pooled six randomized controlled trials of lycopene or tomato-extract supplementation found no significant overall effect on PSA levels.11PubMed. The effect of lycopene supplement from different sources on prostate specific antigen (PSA): A systematic review and meta-analysis of randomized controlled trials
This discrepancy matters. It suggests that while lycopene might help in certain subgroups or at certain stages of disease, it’s not a reliable PSA-lowering agent across the board. If your doctor is monitoring your PSA for a specific concern, eating more watermelon is unlikely to change the number enough to affect clinical decisions. The potential prostate benefits of lycopene likely operate on longer timescales and through mechanisms that don’t neatly map onto a single blood test.
L-Citrulline and Blood Flow to the Pelvis
Lycopene gets the most prostate-specific attention, but watermelon’s other headline compound may matter too, if through a more indirect route. L-citrulline is an amino acid that watermelon contains in unusually high concentrations. Your body converts it into L-arginine, which in turn is used to produce nitric oxide, the molecule that relaxes blood vessel walls and increases blood flow.12PubMed Central. Watermelon Nutritional Composition with a Focus on L-Citrulline and Its Cardioprotective Health Effects-A Narrative Review
Research confirms that supplementing with L-citrulline or consuming watermelon raises plasma arginine levels, decreases blood pressure, and can increase peripheral blood flow.13PubMed. Influence of L-citrulline and watermelon supplementation on vascular function and exercise performance A meta-analysis of randomized controlled trials found that L-citrulline supplementation, including from watermelon, improved measures of vascular function and cardiometabolic risk markers in adults.14PubMed Central. Effects of l-citrulline supplementation and watermelon consumption on longer-term and postprandial vascular function and cardiometabolic risk markers
Why does blood flow matter for the prostate? Because the prostate sits in a vascular neighborhood. Conditions that impair blood flow, like atherosclerosis and metabolic syndrome, are associated with worse urinary symptoms and BPH progression. Better pelvic blood flow may also help explain the connection to erectile function: a small randomized crossover trial found that oral L-citrulline (combined with transresveratrol) significantly improved erectile function scores compared to placebo in men who were already using standard erectile dysfunction medication.15PubMed Central. Oral L-citrulline and Transresveratrol Supplementation Improves Erectile Function in Men With Phosphodiesterase 5 Inhibitors Erectile function and prostate health aren’t the same thing, but they share an anatomical and vascular neighborhood, and improving the circulatory environment serving one tends to benefit the other.
Watermelon as a Natural Diuretic
Men dealing with urinary symptoms from an enlarged prostate often have a complicated relationship with fluids. Staying hydrated matters for kidney health, but drinking too much at the wrong time makes nighttime bathroom trips worse. Watermelon sits in an interesting spot because it’s about 92% water, and research in animal models suggests its pulp extract has genuine diuretic properties, meaning it promotes urine output and increases urinary sodium excretion.16PubMed. Evaluation of anti-urolithiatic and diuretic activities of watermelon (Citrullus lanatus) using in vivo and in vitro experiments
For someone with urinary symptoms, this is a double-edged sword. The mild diuretic effect and high water content mean a big serving of watermelon close to bedtime will almost certainly increase overnight trips to the bathroom. If you’re eating watermelon for the lycopene and citrulline benefits, the practical move is to eat it earlier in the day. The same study also found that watermelon pulp extract reduced calcium oxalate crystal formation in rats, hinting at possible kidney stone prevention, though that finding hasn’t been replicated in humans yet.
Inflammation and What Didn’t Pan Out
Chronic inflammation is a driver of both BPH and prostate cancer, so it’s reasonable to wonder whether watermelon’s antioxidant profile translates into reduced systemic inflammation. A pilot study testing a three-month anti-inflammatory diet that featured watermelon found no statistically significant differences in inflammatory markers or body composition between the intervention and control groups.17PubMed Central. Impact of a 3-Month Anti-inflammatory Dietary Intervention Focusing on Watermelon on Body Habitus, Inflammation, and Metabolic Markers: A Pilot Study It was a small study and may have lacked the statistical power to detect subtle changes, but it’s a reminder that not every plausible mechanism pans out in clinical testing. The lab evidence for lycopene reducing inflammation in prostate cells is real, but eating watermelon hasn’t been shown to meaningfully lower measurable inflammation in an actual person’s blood.
Watermelon Seeds and Other Compounds
Most people spit out or avoid watermelon seeds, but they contain their own set of potentially relevant compounds. Cucurbitacin E, a triterpenoid found in the seeds of cucurbit family plants (which includes watermelon, pumpkin, and squash), has demonstrated anti-cancer effects in laboratory settings, triggering cell death in prostate and lung cancer cell lines and reducing an inflammatory protein that’s linked to cancer progression.18The FASEB Journal. Isolation of cucurbitacin E from pumpkin seed and analysis of its anti‐cancer and anti‐inflammatory activities That said, the concentrations tested in the lab are far higher than what you’d get from chewing on a few seeds, and this research is at an early stage.
Watermelon seeds also contain zinc, magnesium, and healthy fats. Zinc is particularly relevant because the prostate accumulates more zinc than almost any other organ in the body, and zinc levels tend to be depleted in cancerous prostate tissue. But you’d need to eat roasted watermelon seeds in meaningful quantities to get a nutritionally significant dose, and there’s no clinical evidence yet tying watermelon seed consumption specifically to prostate outcomes.
Not All Watermelons Are the Same
If you’re eating watermelon partly for prostate health, variety matters more than you might expect. A study measuring lycopene and citrulline across different watermelon cultivars found substantial variation. Among the varieties tested, ‘Dixielee’ had the highest lycopene content, followed by ‘Sugar Baby’ and ‘Allsweet,’ all of which have red flesh. For citrulline, the highest concentrations showed up in ‘Yellow Doll’ and an experimental line called NC-517.19HortScience. Heritability and Genetic Variance Components Associated with Citrulline, Arginine, and Lycopene Content in Diverse Watermelon Cultigens
The simplest rule of thumb: the deeper the red, the more lycopene. Yellow and orange-fleshed watermelons contain little to no lycopene, though they can still be high in citrulline. If both compounds matter to you, a deep red variety gives you the best of both. Seedless varieties, which dominate grocery stores, generally contain comparable lycopene to seeded ones, so convenience isn’t a meaningful trade-off here. Ripeness also matters; an underripe watermelon that’s pale pink inside has less lycopene than a fully ripe one with saturated red flesh.
Who Should Be Cautious
Watermelon is a safe food for most people, but a few situations warrant attention. Because it has a relatively high glycemic index (it spikes blood sugar faster than many other fruits), men managing diabetes alongside prostate issues should account for it in their carbohydrate planning. The effect is somewhat offset by the fact that a typical serving contains modest total sugar per volume since the fruit is mostly water, but it’s worth knowing.
Men with chronic kidney disease face a more serious concern. Watermelon is high in potassium, and impaired kidneys can’t clear potassium efficiently. For someone with advanced kidney disease, large servings of watermelon could push potassium levels into a dangerous range. If your kidney function is compromised, check with your nephrologist before making watermelon a daily habit.
Finally, the diuretic effect mentioned earlier means watermelon interacts awkwardly with some prostate medications. Alpha-blockers (like tamsulosin) already affect urinary dynamics, and adding a natural diuretic on top can increase urgency or frequency. This isn’t dangerous, but it’s annoying enough that some men stop eating watermelon in the evening without realizing they could just shift their timing to earlier in the day and keep the benefits.
Supplements Versus the Whole Fruit
You can buy lycopene capsules and L-citrulline powder easily enough, and some men prefer that route because it gives them a controlled dose. But there are reasons to favor the whole fruit. The crossover study on watermelon juice showed that fresh watermelon delivered bioavailable lycopene without heat processing, and the cis-isomeric form it provides naturally is the form your body prefers.2The Journal of Nutrition. Consumption of Watermelon Juice Increases Plasma Concentrations of Lycopene and β-Carotene in Humans Whole watermelon also delivers the citrulline, potassium, vitamin C, and water content simultaneously, and there’s growing recognition in nutrition science that compounds from whole foods often interact synergistically in ways isolated supplements don’t replicate.
On the other hand, most of the clinical trial evidence on BPH and prostate cancer used concentrated lycopene supplements, not watermelon itself. The BPH trial that found slowed prostate growth used a lycopene supplement, not dietary watermelon.8PubMed. Lycopene inhibits disease progression in patients with benign prostate hyperplasia So while the bioavailability data supports watermelon as a source, the intervention data showing measurable prostate outcomes mostly comes from supplements delivering higher and more consistent doses than you’d get from casual fruit eating. A reasonable middle path is to enjoy watermelon regularly as part of a lycopene-rich diet (alongside tomato sauce, pink grapefruit, and guava) rather than treating it as a standalone prostate therapy.