The nitrate content of beetroot juice helps lower blood pressure, research has shown.
A study in the US journal Hypertension found that blood pressure was reduced within 24 hours in people who drank beetroot juice or took nitrate tablets.
The higher the blood pressure, the greater the impact of the nitrates.
This research suggests there is hope of using a more "natural" approach to bring down blood pressure. Nitrates are found in a number of vegetables.
A previous study found that drinking a pint of beetroot juice lowered blood pressure significantly in people with normal blood pressure.
Amrita Ahluwalia, author of the study and professor of vascular pharmacology at Barts and the London School of Medicine and Dentistry said they had now proved why.
"We showed that beetroot and nitrate capsules are equally effective in lowering blood pressure, indicating that it is the nitrate content of beetroot juice that underlies its potential to reduce blood pressure," she said.
The research shows that the inorganic nitrate content in beetroot is changed into the gas nitric oxide when eaten. This gas keeps the blood vessels open and relaxed and keeps blood pressure down.
Cardiovascular disease kills over 110,000 people in England every year.
More than 25% of the world's adult population is hypertensive, and it has been estimated that this figure will increase to 30% by 2025.
Eating fruit and vegetables is known to be good for our cardiovascular health.
But researchers say green, leafy vegetables like lettuce and beetroot are best at reducing the risk of strokes and heart attacks because of their high inorganic content, which comes from nitrates in the soil.
"The hope is that we could take a dietary nitrate approach and advise people to eat vegetables with high nitrate content," said Professor Ahluwalia.
Victoria Taylor, senior dietician at the British Heart Foundation, which funded the study said: "Although beetroot was used in this study it seems that the important thing here is the nitrates.
"More research is now needed to confirm these findings and to identify if the same effect is seen with other vegetables.
"The study seems to add more weight to the fact that we need to eat at least five portions of fruit and vegetables each day," she said.
The study also found that men and women reacted differently to beetroot juice.
The decrease in blood pressure after taking beetroot juice was much more pronounced in men.
Researchers say this could be because women are better at naturally processing nitrate in their bodies.