Flavonols Reduce Colorectal Cancer Risk by 76%

Flavonols — naturally occurring antioxidants found especially in beans, onions, apples and tea — may dramatically reduce the recurrence of advanced adenomas, the polyps that are associated with colorectal cancer. A fresh look at data from a randomized dietary intervention trial of more than 2,000 men and women reveals that those consuming the most flavonols were 76% less at risk than those with the lowest flavonol intake.

Flavonols are a subgroup of plant compounds called flavonoids. The findings, published in Cancer Epidemiology Biomarkers & Prevention, add to a growing body of evidence linking consumption of fruits and vegetables rich in flavonols to cancer protection.

Led by Gerd Bobe, PhD, of the National Cancer Institute, the researchers employed a newly updated flavonoid database from the US Department of Agriculture (USDA). The update provides values for 26 selected flavonoid compounds in 393 foods. Researchers applied the new database to food-frequency questionnaires compiled by the Polyp Prevention Trial, a randomized dietary intervention that examined the effect of a low-fat, high-fiber, high-fruit and high-vegetable diet on adenoma recurrence. Bobe and colleagues analyzed participants' diets for total flavonoid consumption, six flavonoid subgroups and 29 individual flavonoids. They then compared this new breakdown to subjects' risk of adenoma recurrence.

The study found no association between total flavonoid intake and adenoma risk. But a sharp difference emerged between the one-quarter of participants consuming the most flavonols and the quarter with the least.

Similar but smaller inverse associations — the more that people consumed, the less their risk — were observed for kaempferol, a specific flavonol found in plants such as beans and arugula; isoflavonoids in general; and two specific isoflavonoids, genistein and formononetin, found in soy products.

It is important to note that this study was conducted among people with a history of colorectal adenoma; it measured rate of recurrence, not primary prevention of colorectal cancer. A strong dose-response relationship was not found, as the results were significant only in comparing top and bottom quartiles of intake.

Without a degree in biochemistry, in any case, it can be a challenge to keep straight flavonols and flavonoids and all their chemical kin in order to decide what to eat. If you concentrate on eating a diet high in vegetables and fruits (and maybe washing it down with some tea), you can do your body good without breaking out a textbook at every meal.

TO LEARN MORE: Cancer Epidemiology Biomarkers & Prevention, June 2008; abstract at . USDA Flavonoid Database

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