The study's seven participants, all men, were given 17 ounces (500 mL) of either natural watermelon juice, watermelon juice enriched with additional citrulline, or a placebo drink an hour before their workouts. Interestingly, the natural juice was just as effective as the enriched juice. The researchers also determined that intestinal cells can absorb more citrulline from watermelon juice than from citrulline supplements, especially when the juice is unpasteurized.

Postmenopausal women experienced improved cardiovascular health after six weeks of taking commercially available watermelon extract supplements containing citrulline and arginine, according to a study published earlier this year by Florida State University physiologist Arturo Figueroa.

And in a 2012 study—also led by Figueroa—such supplements helped alleviate high blood pressure in obese,