Florida State University researchers Dr. Arturo Figueroa and Bahram Arjmandi say watermelon contains the amino acid L-citrulline/L-arginine, which improves arterial function and can help lower aortic blood pressure.
"Watermelon is the richest edible natural source of L-citrulline, which is closely related to L-arginine, the amino acid required for the formation of nitric oxide essential to the regulation of vascular tone and healthy blood pressure," Figueroa says in a statement.
Figueroa says L-citrulline is converted into L-arginine in the body. However, simply consuming L-arginine as a dietary supplement is not an option because it can cause nausea, gastrointestinal tract discomfort and diarrhea, the researchers say.
The pilot study, published in the American Journal of Hypertension, finds improved arterial function and lowered aortic blood pressure in all nine pre-hypertensive adults ages 51-57 -- four men and five women -- who ate therapeutic doses of watermelon daily for six weeks.
Watermelon or watermelon extract is the best natural source for L-citrulline, but it is also available in the synthetic form in pills, Figueroa says.