Eating watermelon can boost a man's libido in a similar way to taking Viagra, researchers at an American university have said.

The researchers say that the red-fleshed fruit contains an ingredient which affects the body's blood vessels in the same way as when a man takes Viagra. They believe that the fruit could be used to help men who suffer from erectile dysfunction.

Watermelons contain an organic compound called citrulline that can trigger blood vessels to relax, much like Viagra does, according to the scientists at the A&M University in Texas.

Dr Bhimu Patel, the leader of the study, said that when watermelon is consumed, citrulline is converted to an amino acid called arginine which improves circulation.

Dr Patel, who is director of the university's Fruit and Vegetable Improvement Centre said, "the more we study watermelons, the more we realize just how amazing a fruit it is in providing natural enhancers to the human body. We've always known that watermelon is good for you, but the list of its very important health benefits grows longer with each study."

"Arginine boosts nitric oxide, which relaxes blood vessels, the same basic effect which Viagra has, and is used to treat erectile dysfunction and possibly even prevent it.

Eating watermelon could also improve the health of the heart, the immune system and even help people who suffer from obesity and type 2 diabetes.

Beneficial ingredients in watermelon and other fruits and vegetables are known as phyto-nutrients, they are naturally occurring compounds which react with the human body to trigger healthy reactions.

While there are many psychological and physiological problems that can cause impotence, extra nitric oxide could help those who need increased blood flow, the researchers have found.

Citrulline is found in higher concentrations in the rind of watermelons than the flesh and because the rind is not commonly eaten, Dr Patil's team are working to breed new varieties with higher concentrations in the flesh.

Almost 92 percent of watermelon is water, but the remaining 8 percent is loaded with lycopene, an anti-oxidant which protects the human heart, the prostate and improves skin health.