Lycopene - an antioxidant found in tomatoes and other fruits - improves blood vessel function in people with heart problems, a University of Cambridge study suggests.

Previous research has shown that people who follow a Mediterranean diet have lower risk of developing heart diseases. Mediterranean diet includes a variety of fruits and vegetables along with whole grains, nuts and a glass of wine.

In the present study, researchers conducted randomised, double blind, placebo-controlled and interventional trial to see whether lycopene from tomatoes helped improve blood vessel function in people with cardiovascular diseases.

"There's a wealth of research that suggests that the Mediterranean diet - which includes lycopene found in tomatoes and other fruit as a component - is good for our cardiovascular health. But so far, it's been a mystery what the underlying mechanisms could be," said Joseph Cheriyan, consultant clinical pharmacologist & physician at the Addenbrooke's Hospital and Associate Lecturer at the University of Cambridge.

The study included 72 participants, of which 36 had cardiovascular disease. Researchers randomly divided participants into two groups: one group received Ateronon (an off-the-shelf supplement containing 7mg of lycopene) or a dummy pill.

Participants' cardiovascular health was assessed using measurements of forearm blood flow. The function of the blood flow is determined by the forearm blood vessels' response to a natural chemical called acetylcholine. Impaired function of the inner lining (endothelium) of the blood vessel predicts future cardiovascular risk.

Researchers found that 7mg of oral lycopene supplement improved blood vessel function in people with heart diseases, but not in healthy patients. The 'tomato' pill, however, had no effects on blood pressure or arterial stiffness.

"We've shown quite clearly that lycopene improves the function of blood vessels in cardiovascular disease patients," added Dr Cheriyan in a news release. "It reinforces the need for a healthy diet in people at risk from heart disease and stroke. A daily 'tomato pill' is not a substitute for other treatments, but may provide added benefits when taken alongside other medication."

The study didn't show if the pills actually reduce heart disease. Researchers said that only further research can find a link between the two.

Lycopene is the substance that gives fruits the red color. Apart from tomatoes, lycopene is also found in watermelons, pink grapefruits and guavas. One cup (240 ml) of tomato juice provides about 23 mg of lycopene, according to Medline Plus.

The study is published in the journal PLOS One. It was funded by Cambridge University Hospitals NHS Foundation Trust and others.