Organically grown fruits and vegetable are healthier than conventionally grown products. A US study reports that organic food may improve your blood pressure and lower the risk of heart disease and stroke.

A ten-year study comparing organic tomatoes with standard produce found almost double the level of flavonoids - a type of antioxidant. It contained higher levels of quercetin and kaempferol aglycones than their conventionally grown counterparts.

Flavonoids have been shown to reduce high blood pressure, lowering the risk of heart disease and stroke.

Alyson Mitchell, a food chemist, who led the research at the University of California, believes that flavonoids can also help to stave off some forms of cancer and dementia.

Dr Alyson Mitchell and colleagues measured the amount of two flavonoids - quercetin and kaempferol - in dried tomato samples that had been collected as part of a long-term study on agricultural methods.

They found that on average they were 79% and 97% higher respectively in the organic tomatoes than in the conventionally grown fruit. Recent research in Europe found that organic tomatoes contained more vitamin C, B-carotene and flavonoids than conventionally grown tomatoes. Organic peaches and organic apple purée were also found to have more antioxidants.

Scientists said the nitrogen level in the soil was different, suggesting the lower levels of flavonoids found in regular tomatoes were due to over fertilization.

Flavonoids are produced as a defense mechanism that can be triggered by nutrient deficiency, such as a lack of nitrogen in the soil. The inorganic nitrogen in conventional fertilizer is easily available to plants and so, the researchers suggests, the lower levels of flavonoids are probably caused by over-fertilization.