An increased intake of antioxidant flavonols from tea, onions, beans, and apples may slash the risk of colorectal cancer by a whopping 76 per cent, suggests a new US study.
Analysis of data from a randomised dietary intervention trial showed that the overall class of flavonoid compounds was not associated with a risk reduction, but flavonols - a sub-group of flavonoids, did significantly reduce risk, according to findings published in this month's Cancer Epidemiology Biomarkers & Prevention.
The study adds to a growing body of science linking increased consumption of flavonol-rich foods, such as fruit and vegetables, to risk reductions for a range of cancers, including lung, pancreatic, and breast cancer.
Almost one million new cases of colorectal cancer are diagnosed every year around the world, according to the World Health Organisation (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, genetics susceptibility is responsible for less than five per cent of cases, according to the WHO, showing the importance of diet to potentially reduce the risk.
Flavonoids, found in certain wine, fruits, vegetables, tea, nuts, and chocolate, have received extensive research due to their potent antioxidant activity and purported 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 fibre 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 analysed dietary consumption of the polyphenols, and, after adjusting for potential confounding factors such as age, fibre 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 per cent reduction in the recurrence of advanced tumours.
Lesser benefits were observed for increased intakes of kaempferol, found in Brussels sprouts and apples, and genistein found in soy, added the researchers.
On the other hand, no benefits were observed for total flavonoid intake, they added.
"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. Writing in the same journal as the new study, 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."
Colorectal cancer is one of the most curable cancers if diagnosis is made early.
Source: Cancer Epidemiology Biomarkers & Prevention
1 June 2008, Volume 17, Pages 1344-1353, doi: 10.1158/1055-9965.EPI-07-0747
"Dietary Flavonoids and Colorectal Adenoma Recurrence in the Polyp Prevention Trial"
Authors: G. Bobe, L.B. Sansbury, P.S. Albert, A.J. Cross, L. Kahle, J. Ashby, M.L. Slattery, B. Caan, E. Paskett, F. Iber, J.W. Kikendall, P. Lance, C. Daston, J.R. Marshall, A. Schatzkin, E. Lanza