Likely owing to the amino acid L-citrulline, watermelon may be considered a 'functional food' potentially allowing lower doses of drugs or preventing hypertension in the first place.
No matter how you slice it, watermelon has a lot going for it - sweet, low calorie, high fiber, nutrient rich - and now, there’s more. Evidence from a pilot study led by food scientists at Florida State University suggests that watermelon can be an effective natural weapon against prehypertension, a precursor to cardiovascular disease. It is the first investigation of its kind in humans.
The study, led by food scientists Arturo Figueroa, PhD, MD, and Bahram H. Arjmandi, PhD, RD, found that when six grams of the amino acids L-citrulline/L-arginine from watermelon extract were administered daily for six weeks, there was improved arterial function and consequently lowered aortic blood pressure in all nine of their prehypertensive subjects (four men and five postmenopausal women, ages 51-57).
Their research, published by the American Journal of Hypertension,(1) is “the first to document improved aortic hemodynamics in prehypertensive but otherwise healthy middle-aged men and women receiving therapeutic doses of watermelon,” Dr. Figueroa says, adding:
• “These findings suggest that this ‘functional food’ has a vasodilatory effect, and one that may prevent prehypertension from progressing to full-blown hypertension, a major risk factor for heart attacks and strokes.
• “Given the encouraging evidence generated by this preliminary study, we hope to continue the research and include a much larger group of participants in the next round.”
“Watermelon is the richest edible natural source of the amino acid L-citrulline [from citrullus, the Latin word for watermelon], which is closely related to L-arginine, the amino acid required for the formation of nitric oxide(2) essential to the regulation of vascular tone and healthy blood pressure,” Dr. Figueroa says.
• Once in the body, the L-citrulline is converted into L-arginine.
• Simply consuming L-arginine as a dietary supplement isn’t an option for many hypertensive adults, said Figueroa, because it can cause nausea, gastrointestinal tract discomfort, and diarrhea.
• In contrast, watermelon is well tolerated. Participants in the Florida State pilot study reported no adverse effects.
And, in addition to the vascular benefits of citrulline, watermelon provides abundant vitamin A, B6, C, fiber, potassium and lycopene, a powerful antioxidant.
Watermelon may even help to reduce serum glucose levels, according to Dr. Arjmandi.
“Cardiovascular disease (CVD) continues to be the leading cause of death in the United States,” he explains. “Generally, Americans have been more concerned about their blood cholesterol levels and dietary cholesterol intakes rather than their overall cardiovascular health risk factors leading to CVD, such as obesity and vascular dysfunction characterized by arterial stiffening and thickness - issues that functional foods such as watermelon can help to mitigate.
“By functional foods,” says Dr. Arjmandi, “we mean those foods scientifically shown to have health-promoting or disease-preventing properties, above and beyond the other intrinsically healthy nutrients they also supply.”
L-citrulline supplementation might allow a reduced dosage of antihypertensive drugs necessary to control blood pressure, says Dr. Figueroa. “Even better, it may prevent the progression from prehypertension to hypertension in the first place.”
While watermelon or watermelon extract is the best natural source for L-citrulline, it is also available in the synthetic form in pills, which Dr. Figueroa used in a previous study of younger, male subjects.
That investigation showed that four weeks of L-citrulline slowed or weakened the increase in aortic blood pressure in response to cold exposure. It was an important finding, says Dr. Figueroa, since there is a greater occurrence of myocardial infarction associated with hypertension during the cold winter months.
Special benefits for older people, chronically ill
He adds, “Individuals with increased blood pressure and arterial stiffness - especially those who are older and those with chronic diseases such as type 2 diabetes - would benefit from L-citrulline in either the synthetic or natural (watermelon) form.
“The optimal dose appears to be four to six grams a day.”
Approximately 60% of U.S. adults are prehypertensive or hypertensive. Prehypertension is characterized by Systolic blood pressure readings of 120-139 millimeters of mercury (mm Hg) over diastolic pressure of 80-89 mm Hg. “Systolic” refers to the blood pressure when the heart is contracting. “Diastolic” reflects the blood pressure when the heart is in a period of relaxation and expansion.
1. "Effects of Watermelon Supplementation on Aortic Blood Pressure and Wave Reflection in Individuals With Prehypertension: A Pilot Study", American Journal of Hypertension, Jul 8, 2010.
2. Note: In this regard, beet juice, another 'functional food' known for its blood pressure-lowering potential, also acts by increasing nitric acid in the stomach, according to research at the University of London.
Source: Florida State University news release, Oct 13, 2010