Eating watercress regularly could help protect against cancer, a study published today has claimed.

The salad leaf contains ingredients that help prevent damage to the body’s cells and DNA, the researchers suggest.

In the study, led by the University of Ulster, 30 men and 30 women, half of whom were smokers, ate 85g of watercress a day - the equivalent of a small bag of pre-prepared salad - for eight weeks, in addition to their regular diet. The results of blood tests on the participants showed a 22.9 per cent reduction in DNA damage to white blood cells. Damage to DNA is considered by scientists to be an important trigger in the development of cancer.

The study, published in the American Journal of Clinical Nutrition, also noted a 100 per cent increase in levels of the molecule lutein and a 33 per cent rise in beta-carotene, both of which possess antioxidant properties, which help cells defend themselves against damage.

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Other foods said to be rich in lutein include peas, spinach, parsley, kale and broccoli, while good sources of beta-carotene are spinach, carrots and red peppers, as well as yellow fruit such as mango, melon and apricots.

The research, which was funded by British watercress suppliers, suggested that increased concentrations of carotenoids - naturally occurring food pigments that contain vitamins -could improve the antioxidant effects.

“The results support the theory that consumption of watercress can be linked to a reduced risk of cancer via decreased damage to DNA and possible modulation of antioxidant status by increasing carotenoid concentrations,” the report concluded.

The benefits of eating watercress were especially notable among smokers, possibly because they had significantly lower antioxidant levels at the start of the research compared with non-smokers, owing to their habit, the study added.

Professor Ian Rowland, who led the project, said he believed the findings were “highly significant”. He said previous studies showed links between higher intakes of cruciferous vegetables – such as broccoli - and a reduced risk of several cancers.

“What makes this study unique is it involves people eating watercress in easily achievable amounts, to see what impact that might have on known bio-markers of cancer risk, such as DNA damage,” he said. “Most studies to date have relied on tests conducted in test tubes or in animals, with chemicals derived from cruciferous vegetables.

“Blood cell DNA damage is an indicator of whole body cancer risk, and the results support the theory that consumption of watercress is linked to an overall reduced risk of cancer at various sites in the body.

“The nature of the study group also means that the results are applicable to the general population eating a normal diet.”

Cancer Research UK said the study was not large enough to show a clear link to a decreased risk of cancer. Dr Anthea Martin, a science information officer at the charity, said: “While the results of this study are interesting, it involved a relatively small number of people. Larger studies are needed to determine whether the effects of watercress on cells seen by the researchers translate into a decreased risk of developing cancer.

“We do know that a healthy, balanced diet, including plenty of vegetables and fruit and limited amounts of red and processed meat, can help reduce the risk of cancer.”

The charity is funding a study of 500,000 people across ten countries looking at the effect of foods on cancer risk.

The watercress study was funded by the Watercress Alliance, which is made up of three producers, Vitacress Salads, Alresford Salads and The Watercress Company.

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