LUBBOCK – Cool, fresh watermelon is a juicy way to top off a Fourth of July cookout – and one that researchers say has effects similar to Viagra – but don't expect it to keep fireworks going long into the night.

AP

A slice of watermelon at the Dallas Farmers Market.

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An ingredient called citrulline can trigger production of arginine, an amino acid that boosts nitric oxide, relaxing blood vessels, similar to what happens when a man takes Viagra, said Bhimu Patil, director of Texas A&M's Fruit and Vegetable Improvement Center. "Watermelon may not be as organ-specific as Viagra, but it's a great way to relax blood vessels without any drug side effects," he said.

WHICH MELONS

More citrulline – about 60 percent – is found in watermelon rind than the flesh and in all colors, but is highest in yellow-fleshed types.

CAUTION

Penelope Perkins-Veazie, a U.S. Department of Agriculture researcher, said Dr. Patil's research is valid but with a caveat: One would need to eat about six cups of watermelon to get enough citrulline to boost the body's arginine level. The problem then is "you tend to run to the bathroom more" because watermelon is a diuretic.

LOTS OF SUGAR

Another issue, she said, is the amount of sugar that much watermelon would spill into the bloodstream – a jolt that can sometimes cause cramping. Dr. Patil said he would like to do future studies on how to reduce the sugar in watermelon.