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Flavonols may slash colorectal cancer risk by strongly inhibiting the recurrence of polyps

Jun 19, 2008

  An increased intake of antioxidant flavonols from tea, onions, beans, and apples may slash the risk of colorectal cancer by a whopping 76 % according to the results of a new US study performed by scientists at the National Cancer Institute, a division of the National Institutes of Health. The analysis of the data was from a randomized dietary intervention trial. The study adds to a growing body of science linking increased consumption of flavonol-rich foods, antioxidants found in particular fruits and vegetables, to risk reductions for a range of cancers, including lung, pancreatic, and breast cancers.

Almost one million new cases of colorectal cancer are diagnosed every year around the world, according to the World Health Organization (WHO). It is the third most common cancer globally. A diet high in fat, refined carbohydrates and animal protein, are reported to increase the risk. Moreover, genetic susceptibility is responsible for less than five % of cases, according to the WHO, showing the importance of diet to potentially reduce the risk. 
The Flavonoids responsible are found in red wines, particular fruits and vegetables, green tea, some nuts, and chocolate. They have received extensive research due to their potent antioxidant activity and myriad health benefits. Many have also been implicated in possible protection against diseases such as cancer and cardiovascular disease.
The researchers, led by Gerd Bobe from the National Cancer Institute, used data from the updated flavonoid database from the US Department of Agriculture to quantify the intake of 29 individual flavonoids, total flavonoids, and six flavonoid subgroups among participants of the Polyp Prevention Trial. The trial studied the effect of a low-fat, high fiber diet, rich in fruit and vegetables on the recurrence of pre-cancerous polyps in the colon and rectum.

     Over 2,000 men and women were randomly assigned to either the 'healthy' diet, or a normal diet. Using food frequency questionnaires, Bobe and co-workers analyzed dietary consumption of the polyphenols, and, after adjusting for potential confounding factors such as age, fiber intake, BMI, sex, and the use of regular non-steroidal anti-inflammatory medication, they found that an increased intake of flavonols was linked to a 76 % reduction in the recurrence of advanced tumors. On the other hand, no benefits were observed for total flavonoid intake other than the flavanols. However, Kaempferol found in Brussels sprouts and apples, and Genistein found in soy, had some protective ability added the researchers. "Our data suggest that a flavonol-rich diet may decrease the risk of advanced adenoma recurrence," concluded Bobe and co-workers.
In 2006, Italian researchers reported that a diet rich in certain flavonoids could reduce the risk of colorectal cancer by over 40 per cent and lead author Marta Rossi said: "The findings of this large study provide support for an inverse association of selected classes of flavonoids with colorectal cancer risk." The new study is published in the June 1st, 2008 issue of the journal Cancer Epidemiology Biomarkers & Prevention.