Watermelon juice may improve blood vessel function and support heart health, according to new research that adds to a growing body of evidence linking the fruit to cardiovascular and metabolic benefits.
Analysis of data from the National Health and Nutrition Examination Survey (NHANES) has shown that both children and adults who regularly eat watermelon tend to have higher-quality diets. These individuals typically consume more dietary fibre, magnesium, potassium, vitamin C, vitamin A, lycopene and other carotenoids, while their intake of added sugars and saturated fat is lower—a finding considered especially relevant given that many people do not meet the recommended daily fruit intake.
Heart and blood vessel benefits
The fruit’s potential to aid circulation centres on two amino acids it contains: L-citrulline and L-arginine. These compounds play a critical role in the production of nitric oxide, a molecule that helps blood vessels relax and expand. Healthy blood vessel flexibility is a hallmark of good circulation and cardiovascular function.
A placebo-controlled clinical trial conducted by Louisiana State University tested the effect of daily watermelon juice consumption on 18 healthy young adults over two weeks. Researchers found that the juice helped maintain vascular function during periods of hyperglycemia—excess glucose in the blood, often associated with diabetes—and also influenced heart rate variability. Further research has suggested that watermelon consumption and L-citrulline supplementation may improve measures of blood vessel pliability and circulation, such as pulse wave velocity and endothelial function.
“We acknowledge that while the sample size was small (18 healthy young men and women) and more research is needed, this study adds to the current body of evidence supporting regular intake of watermelon for cardio-metabolic health,” said Dr Jack Losso, Ph.D., professor at Louisiana State University’s School of Nutrition and Food Sciences.
Some studies have also indicated that watermelon may help lower blood pressure, particularly in individuals with prehypertension or hypertension. Lycopene, an antioxidant abundant in the fruit, has been investigated for its blood-pressure-lowering effects, while the potassium content can help counterbalance the impact of high sodium intake on blood pressure.
Antioxidant power of lycopene
Red watermelon varieties should be especially sought after because they contain the highest levels of lycopene, a naturally occurring pigment that gives the fruit—and other red-coloured fruits and vegetables such as tomatoes—its colour. Lycopene is a powerful antioxidant effective at fighting free radicals, highly reactive molecules linked to premature aging, cancer and dementia.
“Watermelon is a rich source of antioxidants, vitamin C and lycopene – all of which can help reduce oxidative stress and play a role in heart disease prevention,” Dr Losso added.
Beyond lycopene, watermelon provides significant amounts of vitamin C (a two-cup serving supplies 25 percent of the daily recommended intake), vitamin B6 (8 percent), vitamin A, potassium and magnesium—all for just 80 calories. The fruit is also composed of approximately 92 percent water, making it an easy hydrating option during warm weather or after exercise.
Additional health advantages
Observational studies have found an association between diets rich in lycopene and a reduced risk of certain cancers, including prostate, breast and lung cancers, though researchers note that results have been inconsistent and more randomised controlled trials are needed. The antioxidants in watermelon, including lycopene, may also help prevent or delay cataract formation and reduce the risk of age-related macular degeneration, while vitamin A supports corneal health. For skin, vitamin C aids collagen production and wound healing, and vitamin A promotes turnover and repair; together with lycopene, these nutrients offer some protection against UV damage.
Watermelon’s L-citrulline content has been linked to reduced muscle soreness after exercise, and some research suggests it may aid muscle protein synthesis and improve exercise performance, particularly in older adults. The fruit’s high water content and low calorie count make it a filling snack that could support weight management; studies have shown that consuming watermelon can lead to reduced body weight, body mass index and feelings of hunger compared with calorie-equivalent snacks such as cookies. Additionally, watermelon acts as a natural diuretic, increasing urine flow without straining the kidneys, and it helps the liver process ammonia, which can ease the burden on the kidneys. The citrulline in watermelon is also linked to immune function, with a deficiency of the amino acid potentially affecting immune response in individuals with inflammatory conditions.
While the clinical evidence is promising, researchers caution that many studies—particularly those involving L-citrulline and vascular function—have used small sample sizes and that longer-term, larger-scale investigations are needed to confirm the extent of the benefits.